ffmpeg学习日记503-源码-transcode()函数分析
段曦
ffmpeg学习日记503-源码-transcode()函数分析
接着继续main分析：
//获取基准时间，合成要用
current_time = ti = get_benchmark_time_stamps();
if (transcode() < 0)
exit_program(1);
if (do_benchmark) {
int64_t utime, stime, rtime;
current_time = get_benchmark_time_stamps();
utime = current_time.user_usec - ti.user_usec;
stime = current_time.sys_usec - ti.sys_usec;
rtime = current_time.real_usec - ti.real_usec;
av_log(NULL, AV_LOG_INFO,
"bench: utime=%0.3fs stime=%0.3fs rtime=%0.3fs\n",
utime / 1000000.0, stime / 1000000.0, rtime / 1000000.0);
}
av_log(NULL, AV_LOG_DEBUG, "%"PRIu64" frames successfully decoded, %"PRIu64" decoding errors\n",
decode_error_stat[0], decode_error_stat[1]);
if ((decode_error_stat[0] + decode_error_stat[1]) * max_error_rate < decode_error_stat[1])
exit_program(69);
exit_program(received_nb_signals ? 255 : main_return_code);
return main_return_code;
transcode函数是编解码的核心。
transcode定义如下：
/*
* The following code is the main loop of the file converter
*/
//下面的代码是文件转换的核心
static int transcode(void)
{
int ret, i;
AVFormatContext *os;
OutputStream *ost;
InputStream *ist;
int64_t timer_start;
int64_t total_packets_written = 0;
//transcode_init函数不应错过分析，其中不仅有各种数据的初始化，还有输出文件的写头信息操作，文件信息输出
ret = transcode_init();
if (ret < 0)
goto fail;
if (stdin_interaction) {
av_log(NULL, AV_LOG_INFO, "Press [q] to stop, [?] for help\n");
}
//获取基准时间--开始
timer_start = av_gettime_relative();
//如果开启了多线程编解码，则这里会根据输入文件个数，进行线程创建，最大不会超过系统限制，否则报错，ulimit -a进行查看
#if HAVE_THREADS
if ((ret = init_input_threads()) < 0)
goto fail;
#endif
//received_sigterm这个全局变量是在什么时候赋值的？
while (!received_sigterm) {
//获取基准时间--当前
int64_t cur_time= av_gettime_relative();
/* if 'q' pressed, exits */
//检查终端输入处理
if (stdin_interaction)
if (check_keyboard_interaction(cur_time) < 0)
break;
/* check if there's any stream where output is still needed */
//检查是否还有需要输出的流
if (!need_output()) {
av_log(NULL, AV_LOG_VERBOSE, "No more output streams to write to, finishing.\n");
break;
}
//写输出文件的头信息，输入文件解码，输出文件编码，都在此函数中完成
ret = transcode_step();
if (ret < 0 && ret != AVERROR_EOF) {
av_log(NULL, AV_LOG_ERROR, "Error while filtering: %s\n", av_err2str(ret));
break;
}
/* dump report by using the output first video and audio streams */
print_report(0, timer_start, cur_time);
}
#if HAVE_THREADS
free_input_threads();
#endif
/* at the end of stream, we must flush the decoder buffers */
for (i = 0; i < nb_input_streams; i++) {
ist = input_streams[i];
if (!input_files[ist->file_index]->eof_reached) {
//这里再次调用了一次解码，理解为了刷新解码缓存
process_input_packet(ist, NULL, 0);
}
}
flush_encoders();
term_exit();
/* write the trailer if needed and close file */
for (i = 0; i < nb_output_files; i++) {
os = output_files[i]->ctx;
if (!output_files[i]->header_written) {
av_log(NULL, AV_LOG_ERROR,
"Nothing was written into output file %d (%s), because "
"at least one of its streams received no packets.\n",
i, os->url);
continue;
}
//给输出文件写尾信息
if ((ret = av_write_trailer(os)) < 0) {
av_log(NULL, AV_LOG_ERROR, "Error writing trailer of %s: %s\n", os->url, av_err2str(ret));
if (exit_on_error)
exit_program(1);
}
}
/* dump report by using the first video and audio streams */
print_report(1, timer_start, av_gettime_relative());
/* close each encoder */
for (i = 0; i < nb_output_streams; i++) {
ost = output_streams[i];
if (ost->encoding_needed) {
av_freep(&ost->enc_ctx->stats_in);
}
total_packets_written += ost->packets_written;
if (!ost->packets_written && (abort_on_flags & ABORT_ON_FLAG_EMPTY_OUTPUT_STREAM)) {
av_log(NULL, AV_LOG_FATAL, "Empty output on stream %d.\n", i);
exit_program(1);
}
}
if (!total_packets_written && (abort_on_flags & ABORT_ON_FLAG_EMPTY_OUTPUT)) {
av_log(NULL, AV_LOG_FATAL, "Empty output\n");
exit_program(1);
}
/* close each decoder */
for (i = 0; i < nb_input_streams; i++) {
ist = input_streams[i];
if (ist->decoding_needed) {
avcodec_close(ist->dec_ctx);
if (ist->hwaccel_uninit)
ist->hwaccel_uninit(ist->dec_ctx);
}
}
hw_device_free_all();
/* finished ! */
ret = 0;
fail:
#if HAVE_THREADS
free_input_threads();
#endif
if (output_streams) {
for (i = 0; i < nb_output_streams; i++) {
ost = output_streams[i];
if (ost) {
if (ost->logfile) {
if (fclose(ost->logfile))
av_log(NULL, AV_LOG_ERROR,
"Error closing logfile, loss of information possible: %s\n",
av_err2str(AVERROR(errno)));
ost->logfile = NULL;
}
av_freep(&ost->forced_kf_pts);
av_freep(&ost->apad);
av_freep(&ost->disposition);
av_dict_free(&ost->encoder_opts);
av_dict_free(&ost->sws_dict);
av_dict_free(&ost->swr_opts);
av_dict_free(&ost->resample_opts);
}
}
}
return ret;
}
transcode_init定义如下：
static int transcode_init(void)
{
int ret = 0, i, j, k;
AVFormatContext *oc;
OutputStream *ost;
InputStream *ist;
char error[1024] = {0};
for (i = 0; i < nb_filtergraphs; i++) {
FilterGraph *fg = filtergraphs[i];
for (j = 0; j < fg->nb_outputs; j++) {
OutputFilter *ofilter = fg->outputs[j];
if (!ofilter->ost || ofilter->ost->source_index >= 0)
continue;
if (fg->nb_inputs != 1)
continue;
for (k = nb_input_streams-1; k >= 0 ; k--)
if (fg->inputs[0]->ist == input_streams[k])
break;
ofilter->ost->source_index = k;
}
}
/* init framerate emulation */
for (i = 0; i < nb_input_files; i++) {
InputFile *ifile = input_files[i];
if (ifile->rate_emu)
for (j = 0; j < ifile->nb_streams; j++)
input_streams[j + ifile->ist_index]->start = av_gettime_relative();
}
/* init input streams */
for (i = 0; i < nb_input_streams; i++)
if ((ret = init_input_stream(i, error, sizeof(error))) < 0) {
for (i = 0; i < nb_output_streams; i++) {
ost = output_streams[i];
avcodec_close(ost->enc_ctx);
}
goto dump_format;
}
/*
* initialize stream copy and subtitle/data streams.
* Encoded AVFrame based streams will get initialized as follows:
* - when the first AVFrame is received in do_video_out
* - just before the first AVFrame is received in either transcode_step
* or reap_filters due to us requiring the filter chain buffer sink
* to be configured with the correct audio frame size, which is only
* known after the encoder is initialized.
*/
for (i = 0; i < nb_output_streams; i++) {
if (!output_streams[i]->stream_copy &&
(output_streams[i]->enc_ctx->codec_type == AVMEDIA_TYPE_VIDEO ||
output_streams[i]->enc_ctx->codec_type == AVMEDIA_TYPE_AUDIO))
continue;
ret = init_output_stream_wrapper(output_streams[i], NULL, 0);
if (ret < 0)
goto dump_format;
}
/* discard unused programs */
for (i = 0; i < nb_input_files; i++) {
InputFile *ifile = input_files[i];
for (j = 0; j < ifile->ctx->nb_programs; j++) {
AVProgram *p = ifile->ctx->programs[j];
int discard = AVDISCARD_ALL;
for (k = 0; k < p->nb_stream_indexes; k++)
if (!input_streams[ifile->ist_index + p->stream_index[k]]->discard) {
discard = AVDISCARD_DEFAULT;
break;
}
p->discard = discard;
}
}
/* write headers for files with no streams */
//在check_init_output_file函数中对输出文件进行了写文件头的操作
for (i = 0; i < nb_output_files; i++) {
oc = output_files[i]->ctx;
if (oc->oformat->flags & AVFMT_NOSTREAMS && oc->nb_streams == 0) {
ret = check_init_output_file(output_files[i], i);
if (ret < 0)
goto dump_format;
}
}
//下面是一下信息的输出打印
dump_format:
/* dump the stream mapping */
av_log(NULL, AV_LOG_INFO, "Stream mapping:\n");
for (i = 0; i < nb_input_streams; i++) {
ist = input_streams[i];
for (j = 0; j < ist->nb_filters; j++) {
if (!filtergraph_is_simple(ist->filters[j]->graph)) {
av_log(NULL, AV_LOG_INFO, " Stream #%d:%d (%s) -> %s",
ist->file_index, ist->st->index, ist->dec ? ist->dec->name : "?",
ist->filters[j]->name);
if (nb_filtergraphs > 1)
av_log(NULL, AV_LOG_INFO, " (graph %d)", ist->filters[j]->graph->index);
av_log(NULL, AV_LOG_INFO, "\n");
}
}
}
for (i = 0; i < nb_output_streams; i++) {
ost = output_streams[i];
if (ost->attachment_filename) {
/* an attached file */
av_log(NULL, AV_LOG_INFO, " File %s -> Stream #%d:%d\n",
ost->attachment_filename, ost->file_index, ost->index);
continue;
}
if (ost->filter && !filtergraph_is_simple(ost->filter->graph)) {
/* output from a complex graph */
av_log(NULL, AV_LOG_INFO, " %s", ost->filter->name);
if (nb_filtergraphs > 1)
av_log(NULL, AV_LOG_INFO, " (graph %d)", ost->filter->graph->index);
av_log(NULL, AV_LOG_INFO, " -> Stream #%d:%d (%s)\n", ost->file_index,
ost->index, ost->enc ? ost->enc->name : "?");
continue;
}
av_log(NULL, AV_LOG_INFO, " Stream #%d:%d -> #%d:%d",
input_streams[ost->source_index]->file_index,
input_streams[ost->source_index]->st->index,
ost->file_index,
ost->index);
if (ost->sync_ist != input_streams[ost->source_index])
av_log(NULL, AV_LOG_INFO, " [sync #%d:%d]",
ost->sync_ist->file_index,
ost->sync_ist->st->index);
if (ost->stream_copy)
av_log(NULL, AV_LOG_INFO, " (copy)");
else {
const AVCodec *in_codec = input_streams[ost->source_index]->dec;
const AVCodec *out_codec = ost->enc;
const char *decoder_name = "?";
const char *in_codec_name = "?";
const char *encoder_name = "?";
const char *out_codec_name = "?";
const AVCodecDescriptor *desc;
if (in_codec) {
decoder_name = in_codec->name;
desc = avcodec_descriptor_get(in_codec->id);
if (desc)
in_codec_name = desc->name;
if (!strcmp(decoder_name, in_codec_name))
decoder_name = "native";
}
if (out_codec) {
encoder_name = out_codec->name;
desc = avcodec_descriptor_get(out_codec->id);
if (desc)
out_codec_name = desc->name;
if (!strcmp(encoder_name, out_codec_name))
encoder_name = "native";
}
av_log(NULL, AV_LOG_INFO, " (%s (%s) -> %s (%s))",
in_codec_name, decoder_name,
out_codec_name, encoder_name);
}
av_log(NULL, AV_LOG_INFO, "\n");
}
if (ret) {
av_log(NULL, AV_LOG_ERROR, "%s\n", error);
return ret;
}
atomic_store(&transcode_init_done, 1);
return 0;
}
check_init_output_file定义如下：
/* open the muxer when all the streams are initialized */
static int check_init_output_file(OutputFile *of, int file_index)
{
int ret, i;
for (i = 0; i < of->ctx->nb_streams; i++) {
OutputStream *ost = output_streams[of->ost_index + i];
if (!ost->initialized)
return 0;
}
of->ctx->interrupt_callback = int_cb;
//写文件头信息
ret = avformat_write_header(of->ctx, &of->opts);
if (ret < 0) {
av_log(NULL, AV_LOG_ERROR,
"Could not write header for output file #%d "
"(incorrect codec parameters ?): %s\n",
file_index, av_err2str(ret));
return ret;
}
//assert_avoptions(of->opts);
of->header_written = 1;
av_dump_format(of->ctx, file_index, of->ctx->url, 1);
nb_output_dumped++;
if (sdp_filename || want_sdp)
print_sdp();
/* flush the muxing queues */
for (i = 0; i < of->ctx->nb_streams; i++) {
OutputStream *ost = output_streams[of->ost_index + i];
/* try to improve muxing time_base (only possible if nothing has been written yet) */
if (!av_fifo_size(ost->muxing_queue))
ost->mux_timebase = ost->st->time_base;
while (av_fifo_size(ost->muxing_queue)) {
AVPacket *pkt;
av_fifo_generic_read(ost->muxing_queue, &pkt, sizeof(pkt), NULL);
ost->muxing_queue_data_size -= pkt->size;
write_packet(of, pkt, ost, 1);
av_packet_free(&pkt);
}
}
return 0;
}
transcode_step定义如下：
/**
* Run a single step of transcoding.
*
* @return 0 for success, <0 for error
*/
static int transcode_step(void)
{
OutputStream *ost;
InputStream *ist = NULL;
int ret;
//选择一个经过初始化，并且被输入流赋过值的输出流
ost = choose_output();
if (!ost) {
//检查是否不可用，通过unavailable标志
if (got_eagain()) {
//重新设置为可用，重置可用标志
reset_eagain();
av_usleep(10000);
return 0;
}
av_log(NULL, AV_LOG_VERBOSE, "No more inputs to read from, finishing.\n");
return AVERROR_EOF;
}
if (ost->filter && !ost->filter->graph->graph) {
//ifilter_has_all_input_formats函数过滤非音视频流
if (ifilter_has_all_input_formats(ost->filter->graph)) {
//配置一个最简单的输出流，配置内容多是默认值，或者一些固定值
ret = configure_filtergraph(ost->filter->graph);
if (ret < 0) {
av_log(NULL, AV_LOG_ERROR, "Error reinitializing filters!\n");
return ret;
}
}
}
if (ost->filter && ost->filter->graph->graph) {
/*
* Similar case to the early audio initialization in reap_filters.
* Audio is special in ffmpeg.c currently as we depend on lavfi's
* audio frame buffering/creation to get the output audio frame size
* in samples correct. The audio frame size for the filter chain is
* configured during the output stream initialization.
*
* Apparently avfilter_graph_request_oldest (called in
* transcode_from_filter just down the line) peeks. Peeking already
* puts one frame "ready to be given out", which means that any
* update in filter buffer sink configuration afterwards will not
* help us. And yes, even if it would be utilized,
* av_buffersink_get_samples is affected, as it internally utilizes
* the same early exit for peeked frames.
*
* In other words, if avfilter_graph_request_oldest would not make
* further filter chain configuration or usage of
* av_buffersink_get_samples useless (by just causing the return
* of the peeked AVFrame as-is), we could get rid of this additional
* early encoder initialization.
*/
if (av_buffersink_get_type(ost->filter->filter) == AVMEDIA_TYPE_AUDIO)
init_output_stream_wrapper(ost, NULL, 1);
//将输入文件的转码参数，给到输出文件的参数中
if ((ret = transcode_from_filter(ost->filter->graph, &ist)) < 0)
return ret;
if (!ist)
return 0;
} else if (ost->filter) {
int i;
for (i = 0; i < ost->filter->graph->nb_inputs; i++) {
InputFilter *ifilter = ost->filter->graph->inputs[i];
if (!ifilter->ist->got_output && !input_files[ifilter->ist->file_index]->eof_reached) {
ist = ifilter->ist;
break;
}
}
if (!ist) {
ost->inputs_done = 1;
return 0;
}
} else {
av_assert0(ost->source_index >= 0);
ist = input_streams[ost->source_index];
}
//完成编解码工作
ret = process_input(ist->file_index);
if (ret == AVERROR(EAGAIN)) {
if (input_files[ist->file_index]->eagain)
ost->unavailable = 1;
return 0;
}
if (ret < 0)
return ret == AVERROR_EOF ? 0 : ret;
//reap_filters函数也是做的编解码工作，并且process_input中调用了reap_filters，那这里两次编解码函数的调用，没明白逻辑
return reap_filters(0);
}
process_input定义如下：
/*
* Return
* - 0 -- one packet was read and processed
* - AVERROR(EAGAIN) -- no packets were available for selected file,
* this function should be called again
* - AVERROR_EOF -- this function should not be called again
*/
static int process_input(int file_index)
{
InputFile *ifile = input_files[file_index];
AVFormatContext *is;
InputStream *ist;
AVPacket *pkt;
int ret, thread_ret, i, j;
int64_t duration;
int64_t pkt_dts;
int disable_discontinuity_correction = copy_ts;
is = ifile->ctx;
//从输入流中读取一帧数据
ret = get_input_packet(ifile, &pkt);
if (ret == AVERROR(EAGAIN)) {
ifile->eagain = 1;
return ret;
}
if (ret < 0 && ifile->loop) {
AVCodecContext *avctx;
for (i = 0; i < ifile->nb_streams; i++) {
ist = input_streams[ifile->ist_index + i];
avctx = ist->dec_ctx;
if (ist->decoding_needed) {
//对输入文件进行解码操作
ret = process_input_packet(ist, NULL, 1);
if (ret>0)
return 0;
avcodec_flush_buffers(avctx);
}
}
#if HAVE_THREADS
free_input_thread(file_index);
#endif
ret = seek_to_start(ifile, is);
#if HAVE_THREADS
thread_ret = init_input_thread(file_index);
if (thread_ret < 0)
return thread_ret;
#endif
if (ret < 0)
av_log(NULL, AV_LOG_WARNING, "Seek to start failed.\n");
else
ret = get_input_packet(ifile, &pkt);
if (ret == AVERROR(EAGAIN)) {
ifile->eagain = 1;
return ret;
}
}
if (ret < 0) {
if (ret != AVERROR_EOF) {
print_error(is->url, ret);
if (exit_on_error)
exit_program(1);
}
for (i = 0; i < ifile->nb_streams; i++) {
ist = input_streams[ifile->ist_index + i];
if (ist->decoding_needed) {
ret = process_input_packet(ist, NULL, 0);
if (ret>0)
return 0;
}
/* mark all outputs that don't go through lavfi as finished */
for (j = 0; j < nb_output_streams; j++) {
OutputStream *ost = output_streams[j];
if (ost->source_index == ifile->ist_index + i &&
(ost->stream_copy || ost->enc->type == AVMEDIA_TYPE_SUBTITLE))
finish_output_stream(ost);
}
}
ifile->eof_reached = 1;
return AVERROR(EAGAIN);
}
reset_eagain();
if (do_pkt_dump) {
av_pkt_dump_log2(NULL, AV_LOG_INFO, pkt, do_hex_dump,
is->streams[pkt->stream_index]);
}
/* the following test is needed in case new streams appear
dynamically in stream : we ignore them */
if (pkt->stream_index >= ifile->nb_streams) {
report_new_stream(file_index, pkt);
goto discard_packet;
}
ist = input_streams[ifile->ist_index + pkt->stream_index];
ist->data_size += pkt->size;
ist->nb_packets++;
if (ist->discard)
goto discard_packet;
if (pkt->flags & AV_PKT_FLAG_CORRUPT) {
av_log(NULL, exit_on_error ? AV_LOG_FATAL : AV_LOG_WARNING,
"%s: corrupt input packet in stream %d\n", is->url, pkt->stream_index);
if (exit_on_error)
exit_program(1);
}
if (debug_ts) {
av_log(NULL, AV_LOG_INFO, "demuxer -> ist_index:%d type:%s "
"next_dts:%s next_dts_time:%s next_pts:%s next_pts_time:%s pkt_pts:%s pkt_pts_time:%s pkt_dts:%s pkt_dts_time:%s off:%s off_time:%s\n",
ifile->ist_index + pkt->stream_index, av_get_media_type_string(ist->dec_ctx->codec_type),
av_ts2str(ist->next_dts), av_ts2timestr(ist->next_dts, &AV_TIME_BASE_Q),
av_ts2str(ist->next_pts), av_ts2timestr(ist->next_pts, &AV_TIME_BASE_Q),
av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, &ist->st->time_base),
av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, &ist->st->time_base),
av_ts2str(input_files[ist->file_index]->ts_offset),
av_ts2timestr(input_files[ist->file_index]->ts_offset, &AV_TIME_BASE_Q));
}
if(!ist->wrap_correction_done && is->start_time != AV_NOPTS_VALUE && ist->st->pts_wrap_bits < 64){
int64_t stime, stime2;
// Correcting starttime based on the enabled streams
// FIXME this ideally should be done before the first use of starttime but we do not know which are the enabled streams at that point.
// so we instead do it here as part of discontinuity handling
if ( ist->next_dts == AV_NOPTS_VALUE
&& ifile->ts_offset == -is->start_time
&& (is->iformat->flags & AVFMT_TS_DISCONT)) {
int64_t new_start_time = INT64_MAX;
for (i=0; i<is->nb_streams; i++) {
AVStream *st = is->streams[i];
if(st->discard == AVDISCARD_ALL || st->start_time == AV_NOPTS_VALUE)
continue;
new_start_time = FFMIN(new_start_time, av_rescale_q(st->start_time, st->time_base, AV_TIME_BASE_Q));
}
if (new_start_time > is->start_time) {
av_log(is, AV_LOG_VERBOSE, "Correcting start time by %"PRId64"\n", new_start_time - is->start_time);
ifile->ts_offset = -new_start_time;
}
}
stime = av_rescale_q(is->start_time, AV_TIME_BASE_Q, ist->st->time_base);
stime2= stime + (1ULL<<ist->st->pts_wrap_bits);
ist->wrap_correction_done = 1;
if(stime2 > stime && pkt->dts != AV_NOPTS_VALUE && pkt->dts > stime + (1LL<<(ist->st->pts_wrap_bits-1))) {
pkt->dts -= 1ULL<<ist->st->pts_wrap_bits;
ist->wrap_correction_done = 0;
}
if(stime2 > stime && pkt->pts != AV_NOPTS_VALUE && pkt->pts > stime + (1LL<<(ist->st->pts_wrap_bits-1))) {
pkt->pts -= 1ULL<<ist->st->pts_wrap_bits;
ist->wrap_correction_done = 0;
}
}
/* add the stream-global side data to the first packet */
if (ist->nb_packets == 1) {
for (i = 0; i < ist->st->nb_side_data; i++) {
AVPacketSideData *src_sd = &ist->st->side_data[i];
uint8_t *dst_data;
if (src_sd->type == AV_PKT_DATA_DISPLAYMATRIX)
continue;
if (av_packet_get_side_data(pkt, src_sd->type, NULL))
continue;
dst_data = av_packet_new_side_data(pkt, src_sd->type, src_sd->size);
if (!dst_data)
exit_program(1);
memcpy(dst_data, src_sd->data, src_sd->size);
}
}
if (pkt->dts != AV_NOPTS_VALUE)
pkt->dts += av_rescale_q(ifile->ts_offset, AV_TIME_BASE_Q, ist->st->time_base);
if (pkt->pts != AV_NOPTS_VALUE)
pkt->pts += av_rescale_q(ifile->ts_offset, AV_TIME_BASE_Q, ist->st->time_base);
if (pkt->pts != AV_NOPTS_VALUE)
pkt->pts *= ist->ts_scale;
if (pkt->dts != AV_NOPTS_VALUE)
pkt->dts *= ist->ts_scale;
pkt_dts = av_rescale_q_rnd(pkt->dts, ist->st->time_base, AV_TIME_BASE_Q, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
if ((ist->dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO ||
ist->dec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) &&
pkt_dts != AV_NOPTS_VALUE && ist->next_dts == AV_NOPTS_VALUE && !copy_ts
&& (is->iformat->flags & AVFMT_TS_DISCONT) && ifile->last_ts != AV_NOPTS_VALUE) {
int64_t delta = pkt_dts - ifile->last_ts;
if (delta < -1LL*dts_delta_threshold*AV_TIME_BASE ||
delta > 1LL*dts_delta_threshold*AV_TIME_BASE){
ifile->ts_offset -= delta;
av_log(NULL, AV_LOG_DEBUG,
"Inter stream timestamp discontinuity %"PRId64", new offset= %"PRId64"\n",
delta, ifile->ts_offset);
pkt->dts -= av_rescale_q(delta, AV_TIME_BASE_Q, ist->st->time_base);
if (pkt->pts != AV_NOPTS_VALUE)
pkt->pts -= av_rescale_q(delta, AV_TIME_BASE_Q, ist->st->time_base);
}
}
duration = av_rescale_q(ifile->duration, ifile->time_base, ist->st->time_base);
if (pkt->pts != AV_NOPTS_VALUE) {
pkt->pts += duration;
ist->max_pts = FFMAX(pkt->pts, ist->max_pts);
ist->min_pts = FFMIN(pkt->pts, ist->min_pts);
}
if (pkt->dts != AV_NOPTS_VALUE)
pkt->dts += duration;
pkt_dts = av_rescale_q_rnd(pkt->dts, ist->st->time_base, AV_TIME_BASE_Q, AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
if (copy_ts && pkt_dts != AV_NOPTS_VALUE && ist->next_dts != AV_NOPTS_VALUE &&
(is->iformat->flags & AVFMT_TS_DISCONT) && ist->st->pts_wrap_bits < 60) {
int64_t wrap_dts = av_rescale_q_rnd(pkt->dts + (1LL<<ist->st->pts_wrap_bits),
ist->st->time_base, AV_TIME_BASE_Q,
AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX);
if (FFABS(wrap_dts - ist->next_dts) < FFABS(pkt_dts - ist->next_dts)/10)
disable_discontinuity_correction = 0;
}
if ((ist->dec_ctx->codec_type == AVMEDIA_TYPE_VIDEO ||
ist->dec_ctx->codec_type == AVMEDIA_TYPE_AUDIO) &&
pkt_dts != AV_NOPTS_VALUE && ist->next_dts != AV_NOPTS_VALUE &&
!disable_discontinuity_correction) {
int64_t delta = pkt_dts - ist->next_dts;
if (is->iformat->flags & AVFMT_TS_DISCONT) {
if (delta < -1LL*dts_delta_threshold*AV_TIME_BASE ||
delta > 1LL*dts_delta_threshold*AV_TIME_BASE ||
pkt_dts + AV_TIME_BASE/10 < FFMAX(ist->pts, ist->dts)) {
ifile->ts_offset -= delta;
av_log(NULL, AV_LOG_DEBUG,
"timestamp discontinuity for stream #%d:%d "
"(id=%d, type=%s): %"PRId64", new offset= %"PRId64"\n",
ist->file_index, ist->st->index, ist->st->id,
av_get_media_type_string(ist->dec_ctx->codec_type),
delta, ifile->ts_offset);
pkt->dts -= av_rescale_q(delta, AV_TIME_BASE_Q, ist->st->time_base);
if (pkt->pts != AV_NOPTS_VALUE)
pkt->pts -= av_rescale_q(delta, AV_TIME_BASE_Q, ist->st->time_base);
}
} else {
if ( delta < -1LL*dts_error_threshold*AV_TIME_BASE ||
delta > 1LL*dts_error_threshold*AV_TIME_BASE) {
av_log(NULL, AV_LOG_WARNING, "DTS %"PRId64", next:%"PRId64" st:%d invalid dropping\n", pkt->dts, ist->next_dts, pkt->stream_index);
pkt->dts = AV_NOPTS_VALUE;
}
if (pkt->pts != AV_NOPTS_VALUE){
int64_t pkt_pts = av_rescale_q(pkt->pts, ist->st->time_base, AV_TIME_BASE_Q);
delta = pkt_pts - ist->next_dts;
if ( delta < -1LL*dts_error_threshold*AV_TIME_BASE ||
delta > 1LL*dts_error_threshold*AV_TIME_BASE) {
av_log(NULL, AV_LOG_WARNING, "PTS %"PRId64", next:%"PRId64" invalid dropping st:%d\n", pkt->pts, ist->next_dts, pkt->stream_index);
pkt->pts = AV_NOPTS_VALUE;
}
}
}
}
if (pkt->dts != AV_NOPTS_VALUE)
ifile->last_ts = av_rescale_q(pkt->dts, ist->st->time_base, AV_TIME_BASE_Q);
if (debug_ts) {
av_log(NULL, AV_LOG_INFO, "demuxer+ffmpeg -> ist_index:%d type:%s pkt_pts:%s pkt_pts_time:%s pkt_dts:%s pkt_dts_time:%s off:%s off_time:%s\n",
ifile->ist_index + pkt->stream_index, av_get_media_type_string(ist->dec_ctx->codec_type),
av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, &ist->st->time_base),
av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, &ist->st->time_base),
av_ts2str(input_files[ist->file_index]->ts_offset),
av_ts2timestr(input_files[ist->file_index]->ts_offset, &AV_TIME_BASE_Q));
}
sub2video_heartbeat(ist, pkt->pts);
//输入文件的解码，输出文件编码，全部在该函数中
process_input_packet(ist, pkt, 0);
discard_packet:
#if HAVE_THREADS
if (ifile->thread_queue_size)
av_packet_free(&pkt);
else
#endif
av_packet_unref(pkt);
return 0;
}
process_input_packet定义如下：
//pkt为NULL,则表示读到文件结束
/* pkt = NULL means EOF (needed to flush decoder buffers) */
static int process_input_packet(InputStream *ist, const AVPacket *pkt, int no_eof)
{
int ret = 0, i;
int repeating = 0;
int eof_reached = 0;
AVPacket *avpkt;
//输入流的pkt申请空间
if (!ist->pkt && !(ist->pkt = av_packet_alloc()))
return AVERROR(ENOMEM);
avpkt = ist->pkt;
if (!ist->saw_first_ts) {
ist->first_dts =
ist->dts = ist->st->avg_frame_rate.num ? - ist->dec_ctx->has_b_frames * AV_TIME_BASE / av_q2d(ist->st->avg_frame_rate) : 0;
ist->pts = 0;
if (pkt && pkt->pts != AV_NOPTS_VALUE && !ist->decoding_needed) {
ist->first_dts =
ist->dts += av_rescale_q(pkt->pts, ist->st->time_base, AV_TIME_BASE_Q);
ist->pts = ist->dts; //unused but better to set it to a value thats not totally wrong
}
ist->saw_first_ts = 1;
}
if (ist->next_dts == AV_NOPTS_VALUE)
ist->next_dts = ist->dts;
if (ist->next_pts == AV_NOPTS_VALUE)
ist->next_pts = ist->pts;
if (pkt) {
av_packet_unref(avpkt);
ret = av_packet_ref(avpkt, pkt);
if (ret < 0)
return ret;
}
if (pkt && pkt->dts != AV_NOPTS_VALUE) {
ist->next_dts = ist->dts = av_rescale_q(pkt->dts, ist->st->time_base, AV_TIME_BASE_Q);
if (ist->dec_ctx->codec_type != AVMEDIA_TYPE_VIDEO || !ist->decoding_needed)
ist->next_pts = ist->pts = ist->dts;
}
// while we have more to decode or while the decoder did output something on EOF
//解码，while循环解码
while (ist->decoding_needed) {
int64_t duration_dts = 0;
int64_t duration_pts = 0;
int got_output = 0;
int decode_failed = 0;
ist->pts = ist->next_pts;
ist->dts = ist->next_dts;
switch (ist->dec_ctx->codec_type) {
//下面是对音频，视频，字幕的处理，其中有编码
//但是这里有一个问题，就是编码在解码前面，这一点还没有理解
//重点对decode_video进行分析
case AVMEDIA_TYPE_AUDIO:
ret = decode_audio (ist, repeating ? NULL : avpkt, &got_output,
&decode_failed);
av_packet_unref(avpkt);
break;
case AVMEDIA_TYPE_VIDEO:
ret = decode_video (ist, repeating ? NULL : avpkt, &got_output, &duration_pts, !pkt,
&decode_failed);
if (!repeating || !pkt || got_output) {
if (pkt && pkt->duration) {
duration_dts = av_rescale_q(pkt->duration, ist->st->time_base, AV_TIME_BASE_Q);
} else if(ist->dec_ctx->framerate.num != 0 && ist->dec_ctx->framerate.den != 0) {
int ticks= av_stream_get_parser(ist->st) ? av_stream_get_parser(ist->st)->repeat_pict+1 : ist->dec_ctx->ticks_per_frame;
duration_dts = ((int64_t)AV_TIME_BASE *
ist->dec_ctx->framerate.den * ticks) /
ist->dec_ctx->framerate.num / ist->dec_ctx->ticks_per_frame;
}
if(ist->dts != AV_NOPTS_VALUE && duration_dts) {
ist->next_dts += duration_dts;
}else
ist->next_dts = AV_NOPTS_VALUE;
}
if (got_output) {
if (duration_pts > 0) {
ist->next_pts += av_rescale_q(duration_pts, ist->st->time_base, AV_TIME_BASE_Q);
} else {
ist->next_pts += duration_dts;
}
}
av_packet_unref(avpkt);
break;
case AVMEDIA_TYPE_SUBTITLE:
if (repeating)
break;
ret = transcode_subtitles(ist, avpkt, &got_output, &decode_failed);
if (!pkt && ret >= 0)
ret = AVERROR_EOF;
av_packet_unref(avpkt);
break;
default:
return -1;
}
if (ret == AVERROR_EOF) {
eof_reached = 1;
break;
}
if (ret < 0) {
if (decode_failed) {
av_log(NULL, AV_LOG_ERROR, "Error while decoding stream #%d:%d: %s\n",
ist->file_index, ist->st->index, av_err2str(ret));
} else {
av_log(NULL, AV_LOG_FATAL, "Error while processing the decoded "
"data for stream #%d:%d\n", ist->file_index, ist->st->index);
}
if (!decode_failed || exit_on_error)
exit_program(1);
break;
}
if (got_output)
ist->got_output = 1;
if (!got_output)
break;
// During draining, we might get multiple output frames in this loop.
// ffmpeg.c does not drain the filter chain on configuration changes,
// which means if we send multiple frames at once to the filters, and
// one of those frames changes configuration, the buffered frames will
// be lost. This can upset certain FATE tests.
// Decode only 1 frame per call on EOF to appease these FATE tests.
// The ideal solution would be to rewrite decoding to use the new
// decoding API in a better way.
if (!pkt)
break;
repeating = 1;
}
/* after flushing, send an EOF on all the filter inputs attached to the stream */
/* except when looping we need to flush but not to send an EOF */
if (!pkt && ist->decoding_needed && eof_reached && !no_eof) {
int ret = send_filter_eof(ist);
if (ret < 0) {
av_log(NULL, AV_LOG_FATAL, "Error marking filters as finished\n");
exit_program(1);
}
}
//这里的流拷贝就是转码过程
/* handle stream copy */
if (!ist->decoding_needed && pkt) {
ist->dts = ist->next_dts;
switch (ist->dec_ctx->codec_type) {
case AVMEDIA_TYPE_AUDIO:
av_assert1(pkt->duration >= 0);
if (ist->dec_ctx->sample_rate) {
ist->next_dts += ((int64_t)AV_TIME_BASE * ist->dec_ctx->frame_size) /
ist->dec_ctx->sample_rate;
} else {
ist->next_dts += av_rescale_q(pkt->duration, ist->st->time_base, AV_TIME_BASE_Q);
}
break;
case AVMEDIA_TYPE_VIDEO:
if (ist->framerate.num) {
// TODO: Remove work-around for c99-to-c89 issue 7
AVRational time_base_q = AV_TIME_BASE_Q;
int64_t next_dts = av_rescale_q(ist->next_dts, time_base_q, av_inv_q(ist->framerate));
ist->next_dts = av_rescale_q(next_dts + 1, av_inv_q(ist->framerate), time_base_q);
} else if (pkt->duration) {
ist->next_dts += av_rescale_q(pkt->duration, ist->st->time_base, AV_TIME_BASE_Q);
} else if(ist->dec_ctx->framerate.num != 0) {
int ticks= av_stream_get_parser(ist->st) ? av_stream_get_parser(ist->st)->repeat_pict + 1 : ist->dec_ctx->ticks_per_frame;
ist->next_dts += ((int64_t)AV_TIME_BASE *
ist->dec_ctx->framerate.den * ticks) /
ist->dec_ctx->framerate.num / ist->dec_ctx->ticks_per_frame;
}
break;
}
ist->pts = ist->dts;
ist->next_pts = ist->next_dts;
}
for (i = 0; i < nb_output_streams; i++) {
OutputStream *ost = output_streams[i];
if (!ost->pkt && !(ost->pkt = av_packet_alloc()))
exit_program(1);
if (!check_output_constraints(ist, ost) || ost->encoding_needed)
continue;
//转码的具体执行函数
do_streamcopy(ist, ost, pkt);
}
return !eof_reached;
}
decode_video定义如下：
static int decode_video(InputStream *ist, AVPacket *pkt, int *got_output, int64_t *duration_pts, int eof,
int *decode_failed)
{
AVFrame *decoded_frame;
int i, ret = 0, err = 0;
int64_t best_effort_timestamp;
int64_t dts = AV_NOPTS_VALUE;
// With fate-indeo3-2, we're getting 0-sized packets before EOF for some
// reason. This seems like a semi-critical bug. Don't trigger EOF, and
// skip the packet.
if (!eof && pkt && pkt->size == 0)
return 0;
//对过滤帧和解码帧申请内存
if (!ist->decoded_frame && !(ist->decoded_frame = av_frame_alloc()))
return AVERROR(ENOMEM);
if (!ist->filter_frame && !(ist->filter_frame = av_frame_alloc()))
return AVERROR(ENOMEM);
decoded_frame = ist->decoded_frame;
if (ist->dts != AV_NOPTS_VALUE)
dts = av_rescale_q(ist->dts, AV_TIME_BASE_Q, ist->st->time_base);
if (pkt) {
pkt->dts = dts; // ffmpeg.c probably shouldn't do this
}
// The old code used to set dts on the drain packet, which does not work
// with the new API anymore.
if (eof) {
void *new = av_realloc_array(ist->dts_buffer, ist->nb_dts_buffer + 1, sizeof(ist->dts_buffer[0]));
if (!new)
return AVERROR(ENOMEM);
ist->dts_buffer = new;
ist->dts_buffer[ist->nb_dts_buffer++] = dts;
}
update_benchmark(NULL);
//在这里进行了解码操作，只解码一帧，外面的while会不停调用该函数
ret = decode(ist->dec_ctx, decoded_frame, got_output, pkt);
update_benchmark("decode_video %d.%d", ist->file_index, ist->st->index);
if (ret < 0)
*decode_failed = 1;
// The following line may be required in some cases where there is no parser
// or the parser does not has_b_frames correctly
if (ist->st->codecpar->video_delay < ist->dec_ctx->has_b_frames) {
if (ist->dec_ctx->codec_id == AV_CODEC_ID_H264) {
ist->st->codecpar->video_delay = ist->dec_ctx->has_b_frames;
} else
av_log(ist->dec_ctx, AV_LOG_WARNING,
"video_delay is larger in decoder than demuxer %d > %d.\n"
"If you want to help, upload a sample "
"of this file to https://streams.videolan.org/upload/ "
"and contact the ffmpeg-devel mailing list. (ffmpeg-devel@ffmpeg.org)\n",
ist->dec_ctx->has_b_frames,
ist->st->codecpar->video_delay);
}
//检查解码结果，检查依据是InputStream ist的标志位判定
if (ret != AVERROR_EOF)
check_decode_result(ist, got_output, ret);
if (*got_output && ret >= 0) {
if (ist->dec_ctx->width != decoded_frame->width ||
ist->dec_ctx->height != decoded_frame->height ||
ist->dec_ctx->pix_fmt != decoded_frame->format) {
av_log(NULL, AV_LOG_DEBUG, "Frame parameters mismatch context %d,%d,%d != %d,%d,%d\n",
decoded_frame->width,
decoded_frame->height,
decoded_frame->format,
ist->dec_ctx->width,
ist->dec_ctx->height,
ist->dec_ctx->pix_fmt);
}
}
if (!*got_output || ret < 0)
return ret;
if(ist->top_field_first>=0)
decoded_frame->top_field_first = ist->top_field_first;
ist->frames_decoded++;
if (ist->hwaccel_retrieve_data && decoded_frame->format == ist->hwaccel_pix_fmt) {
err = ist->hwaccel_retrieve_data(ist->dec_ctx, decoded_frame);
if (err < 0)
goto fail;
}
ist->hwaccel_retrieved_pix_fmt = decoded_frame->format;
best_effort_timestamp= decoded_frame->best_effort_timestamp;
*duration_pts = decoded_frame->pkt_duration;
if (ist->framerate.num)
best_effort_timestamp = ist->cfr_next_pts++;
if (eof && best_effort_timestamp == AV_NOPTS_VALUE && ist->nb_dts_buffer > 0) {
best_effort_timestamp = ist->dts_buffer[0];
for (i = 0; i < ist->nb_dts_buffer - 1; i++)
ist->dts_buffer[i] = ist->dts_buffer[i + 1];
ist->nb_dts_buffer--;
}
if(best_effort_timestamp != AV_NOPTS_VALUE) {
int64_t ts = av_rescale_q(decoded_frame->pts = best_effort_timestamp, ist->st->time_base, AV_TIME_BASE_Q);
if (ts != AV_NOPTS_VALUE)
ist->next_pts = ist->pts = ts;
}
if (debug_ts) {
av_log(NULL, AV_LOG_INFO, "decoder -> ist_index:%d type:video "
"frame_pts:%s frame_pts_time:%s best_effort_ts:%"PRId64" best_effort_ts_time:%s keyframe:%d frame_type:%d time_base:%d/%d\n",
ist->st->index, av_ts2str(decoded_frame->pts),
av_ts2timestr(decoded_frame->pts, &ist->st->time_base),
best_effort_timestamp,
av_ts2timestr(best_effort_timestamp, &ist->st->time_base),
decoded_frame->key_frame, decoded_frame->pict_type,
ist->st->time_base.num, ist->st->time_base.den);
}
if (ist->st->sample_aspect_ratio.num)
decoded_frame->sample_aspect_ratio = ist->st->sample_aspect_ratio;
//将解码帧送入过滤器，进行编码
//猜测这里极有可能就是使用的边解码边编码的方式，需确认，有研究价值
err = send_frame_to_filters(ist, decoded_frame);
fail:
av_frame_unref(ist->filter_frame);
av_frame_unref(decoded_frame);
return err < 0 ? err : ret;
}
decode定义如下：
//注释翻译：这并不像avcodec_decode_audio4/avcodec_decode_video2那样工作。有以下的区别:如果你有一个帧，你必须用pkt=NULL再次调用它。pkt==NULL的处理方式与pkt->size==0不同(pkt==NULL意味着获得更多输出，pkt->size==0是一个flush/drain packet)
// This does not quite work like avcodec_decode_audio4/avcodec_decode_video2.
// There is the following difference: if you got a frame, you must call
// it again with pkt=NULL. pkt==NULL is treated differently from pkt->size==0
// (pkt==NULL means get more output, pkt->size==0 is a flush/drain packet)
static int decode(AVCodecContext *avctx, AVFrame *frame, int *got_frame, AVPacket *pkt)
{
int ret;
*got_frame = 0;
if (pkt) {
ret = avcodec_send_packet(avctx, pkt);
// In particular, we don't expect AVERROR(EAGAIN), because we read all
// decoded frames with avcodec_receive_frame() until done.
//特别是，我们不期望AVERROR(EAGAIN)，因为我们使用avcodec_receive_frame()读取所有已解码的帧，直到完成。
if (ret < 0 && ret != AVERROR_EOF)
return ret;
}
ret = avcodec_receive_frame(avctx, frame);
if (ret < 0 && ret != AVERROR(EAGAIN))
return ret;
if (ret >= 0)
*got_frame = 1;
return 0;
}
do_streamcopy定义如下：
static void do_streamcopy(InputStream *ist, OutputStream *ost, const AVPacket *pkt)
{
OutputFile *of = output_files[ost->file_index];
InputFile *f = input_files [ist->file_index];
int64_t start_time = (of->start_time == AV_NOPTS_VALUE) ? 0 : of->start_time;
int64_t ost_tb_start_time = av_rescale_q(start_time, AV_TIME_BASE_Q, ost->mux_timebase);
AVPacket *opkt = ost->pkt;
av_packet_unref(opkt);
// EOF: flush output bitstream filters.
if (!pkt) {
//output_packet第四个参数为1时，刷新解码器的缓存，不写入内存队列
output_packet(of, opkt, ost, 1);
return;
}
//下面设置了pts等参数
if ((!ost->frame_number && !(pkt->flags & AV_PKT_FLAG_KEY)) &&
!ost->copy_initial_nonkeyframes)
return;
if (!ost->frame_number && !ost->copy_prior_start) {
int64_t comp_start = start_time;
if (copy_ts && f->start_time != AV_NOPTS_VALUE)
comp_start = FFMAX(start_time, f->start_time + f->ts_offset);
if (pkt->pts == AV_NOPTS_VALUE ?
ist->pts < comp_start :
pkt->pts < av_rescale_q(comp_start, AV_TIME_BASE_Q, ist->st->time_base))
return;
}
if (of->recording_time != INT64_MAX &&
ist->pts >= of->recording_time + start_time) {
close_output_stream(ost);
return;
}
if (f->recording_time != INT64_MAX) {
start_time = f->ctx->start_time;
if (f->start_time != AV_NOPTS_VALUE && copy_ts)
start_time += f->start_time;
if (ist->pts >= f->recording_time + start_time) {
close_output_stream(ost);
return;
}
}
/* force the input stream PTS */
if (ost->enc_ctx->codec_type == AVMEDIA_TYPE_VIDEO)
ost->sync_opts++;
if (av_packet_ref(opkt, pkt) < 0)
exit_program(1);
if (pkt->pts != AV_NOPTS_VALUE)
opkt->pts = av_rescale_q(pkt->pts, ist->st->time_base, ost->mux_timebase) - ost_tb_start_time;
if (pkt->dts == AV_NOPTS_VALUE) {
opkt->dts = av_rescale_q(ist->dts, AV_TIME_BASE_Q, ost->mux_timebase);
} else if (ost->st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) {
int duration = av_get_audio_frame_duration(ist->dec_ctx, pkt->size);
if(!duration)
duration = ist->dec_ctx->frame_size;
opkt->dts = av_rescale_delta(ist->st->time_base, pkt->dts,
(AVRational){1, ist->dec_ctx->sample_rate}, duration,
&ist->filter_in_rescale_delta_last, ost->mux_timebase);
/* dts will be set immediately afterwards to what pts is now */
opkt->pts = opkt->dts - ost_tb_start_time;
} else
opkt->dts = av_rescale_q(pkt->dts, ist->st->time_base, ost->mux_timebase);
opkt->dts -= ost_tb_start_time;
opkt->duration = av_rescale_q(pkt->duration, ist->st->time_base, ost->mux_timebase);
//进行解码
output_packet(of, opkt, ost, 0);
}
output_packet定义如下：
/*
* Send a single packet to the output, applying any bitstream filters
* associated with the output stream. This may result in any number
* of packets actually being written, depending on what bitstream
* filters are applied. The supplied packet is consumed and will be
* blank (as if newly-allocated) when this function returns.
*
* If eof is set, instead indicate EOF to all bitstream filters and
* therefore flush any delayed packets to the output. A blank packet
* must be supplied in this case.
*/
//将单个包发送到输出，应用与输出流相关的任何位流过滤器。这可能会导致实际写入的包的数量，这取决于应用了什么位流过滤器。当该函数返回时，所提供的包将被消耗，并且将为空(就像新分配的一样)。
//如果设置了eof，则指示所有位流过滤器的eof，从而将任何延迟的包刷新到输出。在这种情况下，必须提供空白包装。
static void output_packet(OutputFile *of, AVPacket *pkt,
OutputStream *ost, int eof)
{
int ret = 0;
/* apply the output bitstream filters */
if (ost->bsf_ctx) {
ret = av_bsf_send_packet(ost->bsf_ctx, eof ? NULL : pkt);
if (ret < 0)
goto finish;
while ((ret = av_bsf_receive_packet(ost->bsf_ctx, pkt)) >= 0)
write_packet(of, pkt, ost, 0);
if (ret == AVERROR(EAGAIN))
ret = 0;
} else if (!eof)
write_packet(of, pkt, ost, 0);
finish:
if (ret < 0 && ret != AVERROR_EOF) {
av_log(NULL, AV_LOG_ERROR, "Error applying bitstream filters to an output "
"packet for stream #%d:%d.\n", ost->file_index, ost->index);
if(exit_on_error)
exit_program(1);
}
}
send_frame_to_filters定义如下：
static int send_frame_to_filters(InputStream *ist, AVFrame *decoded_frame)
{
int i, ret;
AVFrame *f;
av_assert1(ist->nb_filters > 0); /* ensure ret is initialized */
for (i = 0; i < ist->nb_filters; i++) {
//从输入流中取出帧或者由参数传入帧
if (i < ist->nb_filters - 1) {
f = ist->filter_frame;
ret = av_frame_ref(f, decoded_frame);
if (ret < 0)
break;
} else
f = decoded_frame;
//将帧数据给过滤器，进行编码
ret = ifilter_send_frame(ist->filters[i], f);
if (ret == AVERROR_EOF)
ret = 0; /* ignore */
if (ret < 0) {
av_log(NULL, AV_LOG_ERROR,
"Failed to inject frame into filter network: %s\n", av_err2str(ret));
break;
}
}
return ret;
}
ifilter_send_frame定义如下：
static int ifilter_send_frame(InputFilter *ifilter, AVFrame *frame)
{
FilterGraph *fg = ifilter->graph;
int need_reinit, ret, i;
/* determine if the parameters for this input changed */
//确定输入的此参数是否已经被更改
need_reinit = ifilter->format != frame->format;
//筛选不同的数据流下的值
switch (ifilter->ist->st->codecpar->codec_type) {
case AVMEDIA_TYPE_AUDIO:
need_reinit |= ifilter->sample_rate != frame->sample_rate ||
ifilter->channels != frame->channels ||
ifilter->channel_layout != frame->channel_layout;
break;
case AVMEDIA_TYPE_VIDEO:
need_reinit |= ifilter->width != frame->width ||
ifilter->height != frame->height;
break;
}
if (!ifilter->ist->reinit_filters && fg->graph)
need_reinit = 0;
if (!!ifilter->hw_frames_ctx != !!frame->hw_frames_ctx ||
(ifilter->hw_frames_ctx && ifilter->hw_frames_ctx->data != frame->hw_frames_ctx->data))
need_reinit = 1;
if (need_reinit) {
//将frame中的参数值填充到过滤器中
ret = ifilter_parameters_from_frame(ifilter, frame);
if (ret < 0)
return ret;
}
/* (re)init the graph if possible, otherwise buffer the frame and return */
//如果可能，重新初始化图形，否则缓存帧并返回
if (need_reinit || !fg->graph) {
for (i = 0; i < fg->nb_inputs; i++) {
if (!ifilter_has_all_input_formats(fg)) {
AVFrame *tmp = av_frame_clone(frame);
if (!tmp)
return AVERROR(ENOMEM);
av_frame_unref(frame);
if (!av_fifo_space(ifilter->frame_queue)) {
ret = av_fifo_realloc2(ifilter->frame_queue, 2 * av_fifo_size(ifilter->frame_queue));
if (ret < 0) {
av_frame_free(&tmp);
return ret;
}
}
av_fifo_generic_write(ifilter->frame_queue, &tmp, sizeof(tmp), NULL);
return 0;
}
}
ret = reap_filters(1);
if (ret < 0 && ret != AVERROR_EOF) {
av_log(NULL, AV_LOG_ERROR, "Error while filtering: %s\n", av_err2str(ret));
return ret;
}
ret = configure_filtergraph(fg);
if (ret < 0) {
av_log(NULL, AV_LOG_ERROR, "Error reinitializing filters!\n");
return ret;
}
}
ret = av_buffersrc_add_frame_flags(ifilter->filter, frame, AV_BUFFERSRC_FLAG_PUSH);
if (ret < 0) {
if (ret != AVERROR_EOF)
av_log(NULL, AV_LOG_ERROR, "Error while filtering: %s\n", av_err2str(ret));
return ret;
}
return 0;
}
reap_filters定义如下：
//收获过滤器？
/**
* Get and encode new output from any of the filtergraphs, without causing
* activity.
*
* @return 0 for success, <0 for severe errors
*/
//在不引起活动的情况下，从任何筛选器中获取并编码新的输出。
static int reap_filters(int flush)
{
AVFrame *filtered_frame = NULL;
int i;
/* Reap all buffers present in the buffer sinks */
//获取缓冲区接收器中存在的所有缓冲区
for (i = 0; i < nb_output_streams; i++) {
OutputStream *ost = output_streams[i];
OutputFile *of = output_files[ost->file_index];
AVFilterContext *filter;
AVCodecContext *enc = ost->enc_ctx;
int ret = 0;
if (!ost->filter || !ost->filter->graph->graph)
continue;
filter = ost->filter->filter;
/*
* Unlike video, with audio the audio frame size matters.
* Currently we are fully reliant on the lavfi filter chain to
* do the buffering deed for us, and thus the frame size parameter
* needs to be set accordingly. Where does one get the required
* frame size? From the initialized AVCodecContext of an audio
* encoder. Thus, if we have gotten to an audio stream, initialize
* the encoder earlier than receiving the first AVFrame.
*/
//与视频不同，对于音频，音频帧的大小很重要。目前我们完全依赖lavfi过滤器链为我们做缓冲行为，因此帧大小参数需要相应地设置。从哪里得到所需的帧大小?从音频编码器的初始化AVCodecContext。因此，如果我们已经到达一个音频流，在接收到第一个AVFrame之前初始化编码器。
if (av_buffersink_get_type(filter) == AVMEDIA_TYPE_AUDIO)
init_output_stream_wrapper(ost, NULL, 1);
if (!ost->pkt && !(ost->pkt = av_packet_alloc())) {
return AVERROR(ENOMEM);
}
if (!ost->filtered_frame && !(ost->filtered_frame = av_frame_alloc())) {
return AVERROR(ENOMEM);
}
filtered_frame = ost->filtered_frame;
while (1) {
//av_buffersink_get_frame_flags和av_buffersink_get_type是缓存过滤器的一部分，缓冲器和缓冲器过滤器用于将过滤器图连接到应用程序。它们只有一个连接到图形的输入，没有输出。帧必须使用av_buffersink_get_frame()或av_buffersink_get_samples()提取。
//这里不是很懂这个缓存过滤器干嘛的，下面也没有用到上面提到的函数
ret = av_buffersink_get_frame_flags(filter, filtered_frame,
AV_BUFFERSINK_FLAG_NO_REQUEST);
if (ret < 0) {
if (ret != AVERROR(EAGAIN) && ret != AVERROR_EOF) {
av_log(NULL, AV_LOG_WARNING,
"Error in av_buffersink_get_frame_flags(): %s\n", av_err2str(ret));
} else if (flush && ret == AVERROR_EOF) {
if (av_buffersink_get_type(filter) == AVMEDIA_TYPE_VIDEO)
do_video_out(of, ost, NULL);
}
break;
}
if (ost->finished) {
av_frame_unref(filtered_frame);
continue;
}
switch (av_buffersink_get_type(filter)) {
case AVMEDIA_TYPE_VIDEO:
if (!ost->frame_aspect_ratio.num)
enc->sample_aspect_ratio = filtered_frame->sample_aspect_ratio;
do_video_out(of, ost, filtered_frame);
break;
case AVMEDIA_TYPE_AUDIO:
if (!(enc->codec->capabilities & AV_CODEC_CAP_PARAM_CHANGE) &&
enc->channels != filtered_frame->channels) {
av_log(NULL, AV_LOG_ERROR,
"Audio filter graph output is not normalized and encoder does not support parameter changes\n");
break;
}
do_audio_out(of, ost, filtered_frame);
break;
default:
// TODO support subtitle filters
av_assert0(0);
}
av_frame_unref(filtered_frame);
}
}
return 0;
}
do_video_out定义如下：
static void do_video_out(OutputFile *of,
OutputStream *ost,
AVFrame *next_picture)
{
int ret, format_video_sync;
AVPacket *pkt = ost->pkt;
AVCodecContext *enc = ost->enc_ctx;
AVRational frame_rate;
int nb_frames, nb0_frames, i;
double delta, delta0;
double duration = 0;
double sync_ipts = AV_NOPTS_VALUE;
int frame_size = 0;
InputStream *ist = NULL;
AVFilterContext *filter = ost->filter->filter;
init_output_stream_wrapper(ost, next_picture, 1);
sync_ipts = adjust_frame_pts_to_encoder_tb(of, ost, next_picture);
if (ost->source_index >= 0)
ist = input_streams[ost->source_index];
//在这里调用了这个缓存过滤器
frame_rate = av_buffersink_get_frame_rate(filter);
if (frame_rate.num > 0 && frame_rate.den > 0)
duration = 1/(av_q2d(frame_rate) * av_q2d(enc->time_base));
if(ist && ist->st->start_time != AV_NOPTS_VALUE && ist->first_dts != AV_NOPTS_VALUE && ost->frame_rate.num)
duration = FFMIN(duration, 1/(av_q2d(ost->frame_rate) * av_q2d(enc->time_base)));
if (!ost->filters_script &&
!ost->filters &&
(nb_filtergraphs == 0 || !filtergraphs[0]->graph_desc) &&
next_picture &&
ist &&
lrintf(next_picture->pkt_duration * av_q2d(ist->st->time_base) / av_q2d(enc->time_base)) > 0) {
duration = lrintf(next_picture->pkt_duration * av_q2d(ist->st->time_base) / av_q2d(enc->time_base));
}
if (!next_picture) {
//end, flushing
//mid_pred,一段根据不同平台的汇编代码，效率杠杆滴吧
nb0_frames = nb_frames = mid_pred(ost->last_nb0_frames[0],
ost->last_nb0_frames[1],
ost->last_nb0_frames[2]);
} else {
delta0 = sync_ipts - ost->sync_opts; // delta0 is the "drift" between the input frame (next_picture) and where it would fall in the output.
delta = delta0 + duration;
/* by default, we output a single frame */
nb0_frames = 0; // tracks the number of times the PREVIOUS frame should be duplicated, mostly for variable framerate (VFR)
nb_frames = 1;
format_video_sync = video_sync_method;
if (format_video_sync == VSYNC_AUTO) {
if(!strcmp(of->ctx->oformat->name, "avi")) {
format_video_sync = VSYNC_VFR;
} else
format_video_sync = (of->ctx->oformat->flags & AVFMT_VARIABLE_FPS) ? ((of->ctx->oformat->flags & AVFMT_NOTIMESTAMPS) ? VSYNC_PASSTHROUGH : VSYNC_VFR) : VSYNC_CFR;
if ( ist
&& format_video_sync == VSYNC_CFR
&& input_files[ist->file_index]->ctx->nb_streams == 1
&& input_files[ist->file_index]->input_ts_offset == 0) {
format_video_sync = VSYNC_VSCFR;
}
if (format_video_sync == VSYNC_CFR && copy_ts) {
format_video_sync = VSYNC_VSCFR;
}
}
ost->is_cfr = (format_video_sync == VSYNC_CFR || format_video_sync == VSYNC_VSCFR);
if (delta0 < 0 &&
delta > 0 &&
format_video_sync != VSYNC_PASSTHROUGH &&
format_video_sync != VSYNC_DROP) {
if (delta0 < -0.6) {
av_log(NULL, AV_LOG_VERBOSE, "Past duration %f too large\n", -delta0);
} else
av_log(NULL, AV_LOG_DEBUG, "Clipping frame in rate conversion by %f\n", -delta0);
sync_ipts = ost->sync_opts;
duration += delta0;
delta0 = 0;
}
switch (format_video_sync) {
case VSYNC_VSCFR:
if (ost->frame_number == 0 && delta0 >= 0.5) {
av_log(NULL, AV_LOG_DEBUG, "Not duplicating %d initial frames\n", (int)lrintf(delta0));
delta = duration;
delta0 = 0;
ost->sync_opts = llrint(sync_ipts);
}
case VSYNC_CFR:
// FIXME set to 0.5 after we fix some dts/pts bugs like in avidec.c
if (frame_drop_threshold && delta < frame_drop_threshold && ost->frame_number) {
nb_frames = 0;
} else if (delta < -1.1)
nb_frames = 0;
else if (delta > 1.1) {
nb_frames = lrintf(delta);
if (delta0 > 1.1)
nb0_frames = llrintf(delta0 - 0.6);
}
break;
case VSYNC_VFR:
if (delta <= -0.6)
nb_frames = 0;
else if (delta > 0.6)
ost->sync_opts = llrint(sync_ipts);
break;
case VSYNC_DROP:
case VSYNC_PASSTHROUGH:
ost->sync_opts = llrint(sync_ipts);
break;
default:
av_assert0(0);
}
}
nb_frames = FFMIN(nb_frames, ost->max_frames - ost->frame_number);
nb0_frames = FFMIN(nb0_frames, nb_frames);
memmove(ost->last_nb0_frames + 1,
ost->last_nb0_frames,
sizeof(ost->last_nb0_frames[0]) * (FF_ARRAY_ELEMS(ost->last_nb0_frames) - 1));
ost->last_nb0_frames[0] = nb0_frames;
if (nb0_frames == 0 && ost->last_dropped) {
nb_frames_drop++;
av_log(NULL, AV_LOG_VERBOSE,
"*** dropping frame %d from stream %d at ts %"PRId64"\n",
ost->frame_number, ost->st->index, ost->last_frame->pts);
}
if (nb_frames > (nb0_frames && ost->last_dropped) + (nb_frames > nb0_frames)) {
if (nb_frames > dts_error_threshold * 30) {
av_log(NULL, AV_LOG_ERROR, "%d frame duplication too large, skipping\n", nb_frames - 1);
nb_frames_drop++;
return;
}
nb_frames_dup += nb_frames - (nb0_frames && ost->last_dropped) - (nb_frames > nb0_frames);
av_log(NULL, AV_LOG_VERBOSE, "*** %d dup!\n", nb_frames - 1);
if (nb_frames_dup > dup_warning) {
av_log(NULL, AV_LOG_WARNING, "More than %d frames duplicated\n", dup_warning);
dup_warning *= 10;
}
}
ost->last_dropped = nb_frames == nb0_frames && next_picture;
/* duplicates frame if needed */
for (i = 0; i < nb_frames; i++) {
AVFrame *in_picture;
int forced_keyframe = 0;
double pts_time;
if (i < nb0_frames && ost->last_frame) {
in_picture = ost->last_frame;
} else
in_picture = next_picture;
if (!in_picture)
return;
in_picture->pts = ost->sync_opts;
if (!check_recording_time(ost))
return;
in_picture->quality = enc->global_quality;
in_picture->pict_type = 0;
if (ost->forced_kf_ref_pts == AV_NOPTS_VALUE &&
in_picture->pts != AV_NOPTS_VALUE)
ost->forced_kf_ref_pts = in_picture->pts;
pts_time = in_picture->pts != AV_NOPTS_VALUE ?
(in_picture->pts - ost->forced_kf_ref_pts) * av_q2d(enc->time_base) : NAN;
if (ost->forced_kf_index < ost->forced_kf_count &&
in_picture->pts >= ost->forced_kf_pts[ost->forced_kf_index]) {
ost->forced_kf_index++;
forced_keyframe = 1;
} else if (ost->forced_keyframes_pexpr) {
double res;
ost->forced_keyframes_expr_const_values[FKF_T] = pts_time;
res = av_expr_eval(ost->forced_keyframes_pexpr,
ost->forced_keyframes_expr_const_values, NULL);
ff_dlog(NULL, "force_key_frame: n:%f n_forced:%f prev_forced_n:%f t:%f prev_forced_t:%f -> res:%f\n",
ost->forced_keyframes_expr_const_values[FKF_N],
ost->forced_keyframes_expr_const_values[FKF_N_FORCED],
ost->forced_keyframes_expr_const_values[FKF_PREV_FORCED_N],
ost->forced_keyframes_expr_const_values[FKF_T],
ost->forced_keyframes_expr_const_values[FKF_PREV_FORCED_T],
res);
if (res) {
forced_keyframe = 1;
ost->forced_keyframes_expr_const_values[FKF_PREV_FORCED_N] =
ost->forced_keyframes_expr_const_values[FKF_N];
ost->forced_keyframes_expr_const_values[FKF_PREV_FORCED_T] =
ost->forced_keyframes_expr_const_values[FKF_T];
ost->forced_keyframes_expr_const_values[FKF_N_FORCED] += 1;
}
ost->forced_keyframes_expr_const_values[FKF_N] += 1;
} else if ( ost->forced_keyframes
&& !strncmp(ost->forced_keyframes, "source", 6)
&& in_picture->key_frame==1
&& !i) {
forced_keyframe = 1;
}
if (forced_keyframe) {
in_picture->pict_type = AV_PICTURE_TYPE_I;
av_log(NULL, AV_LOG_DEBUG, "Forced keyframe at time %f\n", pts_time);
}
update_benchmark(NULL);
if (debug_ts) {
av_log(NULL, AV_LOG_INFO, "encoder <- type:video "
"frame_pts:%s frame_pts_time:%s time_base:%d/%d\n",
av_ts2str(in_picture->pts), av_ts2timestr(in_picture->pts, &enc->time_base),
enc->time_base.num, enc->time_base.den);
}
ost->frames_encoded++;
//发送编码帧
ret = avcodec_send_frame(enc, in_picture);
if (ret < 0)
goto error;
// Make sure Closed Captions will not be duplicated
av_frame_remove_side_data(in_picture, AV_FRAME_DATA_A53_CC);
while (1) {
av_packet_unref(pkt);
//进行帧编码
ret = avcodec_receive_packet(enc, pkt);
update_benchmark("encode_video %d.%d", ost->file_index, ost->index);
if (ret == AVERROR(EAGAIN))
break;
if (ret < 0)
goto error;
if (debug_ts) {
av_log(NULL, AV_LOG_INFO, "encoder -> type:video "
"pkt_pts:%s pkt_pts_time:%s pkt_dts:%s pkt_dts_time:%s\n",
av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, &enc->time_base),
av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, &enc->time_base));
}
if (pkt->pts == AV_NOPTS_VALUE && !(enc->codec->capabilities & AV_CODEC_CAP_DELAY))
pkt->pts = ost->sync_opts;
av_packet_rescale_ts(pkt, enc->time_base, ost->mux_timebase);
if (debug_ts) {
av_log(NULL, AV_LOG_INFO, "encoder -> type:video "
"pkt_pts:%s pkt_pts_time:%s pkt_dts:%s pkt_dts_time:%s\n",
av_ts2str(pkt->pts), av_ts2timestr(pkt->pts, &ost->mux_timebase),
av_ts2str(pkt->dts), av_ts2timestr(pkt->dts, &ost->mux_timebase));
}
frame_size = pkt->size;
//这里的第四个参数是0，将流放进入二进制流过滤器，并且写入内存队列
output_packet(of, pkt, ost, 0);
/* if two pass, output log */
if (ost->logfile && enc->stats_out) {
fprintf(ost->logfile, "%s", enc->stats_out);
}
}
ost->sync_opts++;
/*
* For video, number of frames in == number of packets out.
* But there may be reordering, so we can't throw away frames on encoder
* flush, we need to limit them here, before they go into encoder.
*/
ost->frame_number++;
if (vstats_filename && frame_size)
//输出编码后的视频信息
do_video_stats(ost, frame_size);
}
if (!ost->last_frame)
ost->last_frame = av_frame_alloc();
av_frame_unref(ost->last_frame);
if (next_picture && ost->last_frame)
av_frame_ref(ost->last_frame, next_picture);
else
av_frame_free(&ost->last_frame);
return;
error:
av_log(NULL, AV_LOG_FATAL, "Video encoding failed\n");
exit_program(1);
}
总结
1.基本上的编解码流程梳理出个大概，但是其中还存在很多不能理解的地方
- 个别函数的调用关系
- 过滤器的用法，整个结构就是围绕过滤器来获取，设置参数的
- 编解码的流程，现在我理解的编解码函数，在流程中前后分别调用了3次，有点混乱
- 编码之后的文件输出问题，文件输出在哪里，现在只看到编码之后写入了队列里
- 指令中不同的参数对应编解码是如何处理的，前面源码分析一和二只是分析出将指令转换成dict存在了内存中，但是这里没有注意到如何使用
- bsf是什么？什么作用？和编解码的关系？
- fifo结构是什么 ？什么作用？
- buffersink结构是什么？什么作用？
以上这些问题都有待研究。
2.到此为止，ffmpeg工具的整个main函数算是分析完了，内容很多，需要慢慢消化。目前只是单纯的一个调用关系，其中的一些设计精髓，巧妙用法有待发掘。
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