open_output_file函数
杨安歌
open_output_file函数介绍
涉及到的结构体和变量在ffmpeg.c中的定义
OutputStream **output_streams = NULL;
int nb_output_streams = 0;
OutputFile **output_files = NULL;
int nb_output_files = 0;open_output_file()
1、为此文件每个输入流创建一个输出流
2、完成对output_files链表的填写。
3、对命令行参数的设置值进行处理。（这里没有分析全，待以后补充）
static int open_output_file(OptionsContext *o, const char *filename)
{
AVFormatContext *oc;
int i, j, err;
AVOutputFormat *file_oformat;
OutputFile *of;
OutputStream *ost;
InputStream *ist;
AVDictionary *unused_opts = NULL;
AVDictionaryEntry *e = NULL;
//o->stop_time对应参数"-to"，o->recording_time对应参数"t"
if (o->stop_time != INT64_MAX && o->recording_time != INT64_MAX) {
o->stop_time = INT64_MAX;
av_log(NULL, AV_LOG_WARNING, "-t and -to cannot be used together; using -t.\n");
}
if (o->stop_time != INT64_MAX && o->recording_time == INT64_MAX) {
//o->start_time对应参数"-ss"
int64_t start_time = o->start_time == AV_NOPTS_VALUE ? 0 : o->start_time;
if (o->stop_time <= start_time) {
av_log(NULL, AV_LOG_ERROR, "-to value smaller than -ss; aborting.\n");
exit_program(1);
} else {
o->recording_time = o->stop_time - start_time;
}
}
GROW_ARRAY(output_files, nb_output_files);
of = av_mallocz(sizeof(*of));
if (!of)
exit_program(1);
output_files[nb_output_files - 1] = of;
of->ost_index = nb_output_streams;
of->recording_time = o->recording_time;
of->start_time = o->start_time;
of->limit_filesize = o->limit_filesize;//对应参数"fs"
of->shortest = o->shortest;//对应参数"shortest"
av_dict_copy(&of->opts, o->g->format_opts, 0);
if (!strcmp(filename, "-"))
filename = "pipe:";
//对应参数“-f”根据此参数和filename分配一个输出文件格式结构体变量oc，
err = avformat_alloc_output_context2(&oc, NULL, o->format, filename);
if (!oc) {
print_error(filename, err);
exit_program(1);
}
of->ctx = oc;
if (o->recording_time != INT64_MAX)
oc->duration = o->recording_time;
file_oformat= oc->oformat;
oc->interrupt_callback = int_cb;
/* create streams for all unlabeled output pads
*参数"filter","filter_script","reinit_filter","filter_complex",
"lavfi","filter_complex_script"会涉及到此处处理
*/
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->out_tmp || ofilter->out_tmp->name)
continue;
switch (ofilter->type) {
case AVMEDIA_TYPE_VIDEO: o->video_disable = 1; break;
case AVMEDIA_TYPE_AUDIO: o->audio_disable = 1; break;
case AVMEDIA_TYPE_SUBTITLE: o->subtitle_disable = 1; break;
}
init_output_filter(ofilter, o, oc);
}
}
/* ffserver seeking with date=... needs a date reference */
if (!strcmp(file_oformat->name, "ffm") &&
av_strstart(filename, "http:", NULL)) {
int err = parse_option(o, "metadata", "creation_time=now", options);
if (err < 0) {
print_error(filename, err);
exit_program(1);
}
}
if (!strcmp(file_oformat->name, "ffm") && !override_ffserver &&
av_strstart(filename, "http:", NULL)) {
int j;
/* special case for files sent to ffserver: we get the stream
parameters from ffserver */
int err = read_ffserver_streams(o, oc, filename);
if (err < 0) {
print_error(filename, err);
exit_program(1);
}
for(j = nb_output_streams - oc->nb_streams; j < nb_output_streams; j++) {
ost = output_streams[j];
for (i = 0; i < nb_input_streams; i++) {
ist = input_streams[i];
if(ist->st->codec->codec_type == ost->st->codec->codec_type){
ost->sync_ist= ist;
ost->source_index= i;
if(ost->st->codec->codec_type == AVMEDIA_TYPE_AUDIO) ost->avfilter = av_strdup("anull");
if(ost->st->codec->codec_type == AVMEDIA_TYPE_VIDEO) ost->avfilter = av_strdup("null");
ist->discard = 0;
ist->st->discard = ist->user_set_discard;
break;
}
}
if(!ost->sync_ist){
av_log(NULL, AV_LOG_FATAL, "Missing %s stream which is required by this ffm\n", av_get_media_type_string(ost->st->codec->codec_type));
exit_program(1);
}
}
} else if (!o->nb_stream_maps) {//对应参数"map"
char *subtitle_codec_name = NULL;
/* pick the "best" stream of each type */
//开始处理视频流
/* video: highest resolution
o->video_disable对应参数"vn" 下面是找出分辨率最大的那路视频流的下标*/
if (!o->video_disable && av_guess_codec(oc->oformat, NULL, filename, NULL, AVMEDIA_TYPE_VIDEO) != AV_CODEC_ID_NONE) {
int area = 0, idx = -1;
//Test if the given container can store a codec.检查是否此容器能存储这个编码的流，返回1为能，0为不能，负数为信息不可用
int qcr = avformat_query_codec(oc->oformat, oc->oformat->video_codec, 0);
for (i = 0; i < nb_input_streams; i++) {
int new_area;
ist = input_streams[i];
new_area = ist->st->codec->width * ist->st->codec->height + 100000000*!!ist->st->codec_info_nb_frames;
if((qcr!=MKTAG('A', 'P', 'I', 'C')) && (ist->st->disposition & AV_DISPOSITION_ATTACHED_PIC))
new_area = 1;
if (ist->st->codec->codec_type == AVMEDIA_TYPE_VIDEO &&
new_area > area) {
if((qcr==MKTAG('A', 'P', 'I', 'C')) && !(ist->st->disposition & AV_DISPOSITION_ATTACHED_PIC))
continue;
area = new_area;
idx = i;
}
}
if (idx >= 0)
new_video_stream(o, oc, idx);//为输出文件添加一路视频流，将在后面讨论
}
//开始处理音频流
/* audio: most channels */
if (!o->audio_disable && av_guess_codec(oc->oformat, NULL, filename, NULL, AVMEDIA_TYPE_AUDIO) != AV_CODEC_ID_NONE) {
int best_score = 0, idx = -1;
for (i = 0; i < nb_input_streams; i++) {
int score;
ist = input_streams[i];
score = ist->st->codec->channels + 100000000*!!ist->st->codec_info_nb_frames;
if (ist->st->codec->codec_type == AVMEDIA_TYPE_AUDIO &&
score > best_score) {
best_score = score;
idx = i;
}
}
if (idx >= 0)
new_audio_stream(o, oc, idx);
}
//开始处理字幕流
/* subtitles: pick first */
MATCH_PER_TYPE_OPT(codec_names, str, subtitle_codec_name, oc, "s");
if (!o->subtitle_disable && (avcodec_find_encoder(oc->oformat->subtitle_codec) || subtitle_codec_name)) {
for (i = 0; i < nb_input_streams; i++)
if (input_streams[i]->st->codec->codec_type == AVMEDIA_TYPE_SUBTITLE) {
AVCodecDescriptor const *input_descriptor =
avcodec_descriptor_get(input_streams[i]->st->codec->codec_id);
AVCodecDescriptor const *output_descriptor = NULL;
AVCodec const *output_codec =
avcodec_find_encoder(oc->oformat->subtitle_codec);
int input_props = 0, output_props = 0;
if (output_codec)
output_descriptor = avcodec_descriptor_get(output_codec->id);
if (input_descriptor)
input_props = input_descriptor->props & (AV_CODEC_PROP_TEXT_SUB | AV_CODEC_PROP_BITMAP_SUB);
if (output_descriptor)
output_props = output_descriptor->props & (AV_CODEC_PROP_TEXT_SUB | AV_CODEC_PROP_BITMAP_SUB);
if (subtitle_codec_name ||
input_props & output_props ||
// Map dvb teletext which has neither property to any output subtitle encoder
input_descriptor && output_descriptor &&
(!input_descriptor->props ||
!output_descriptor->props)) {
new_subtitle_stream(o, oc, i);
break;
}
}
}
//开始处理数据流
/* Data only if codec id match */
if (!o->data_disable ) {
enum AVCodecID codec_id = av_guess_codec(oc->oformat, NULL, filename, NULL, AVMEDIA_TYPE_DATA);
for (i = 0; codec_id != AV_CODEC_ID_NONE && i < nb_input_streams; i++) {
if (input_streams[i]->st->codec->codec_type == AVMEDIA_TYPE_DATA
&& input_streams[i]->st->codec->codec_id == codec_id )
new_data_stream(o, oc, i);
}
}
} else {
//对应参数"map"
/*
-map [-]input_file_id[:stream_specifier][,sync_file_id[:stream_specifier]] | [linklabel] (output)
两个标示符都是从0开始的。如果被指定，sync_file_id:stream_specifier 设置哪个输入流被用作一个预设同步引用。
第一个-map选项在命令行指定了输出流0的输入源，
第二个-map选项指定了输出流1的输入源，等等。
在流标示符之前的一个 - 字符创建一个'负'的映射。它禁用了从已经创建的映射匹配流。
另一个[LinkLabel]形式，会从复杂过滤图映射输出(参见-filter_complex选项)到输出文件。
LinkLabel必须对应一个定义的图中的输出链接标签。
*/
for (i = 0; i < o->nb_stream_maps; i++) {
StreamMap *map = &o->stream_maps[i];
if (map->disabled)
continue;
if (map->linklabel) {
FilterGraph *fg;
OutputFilter *ofilter = NULL;
int j, k;
for (j = 0; j < nb_filtergraphs; j++) {
fg = filtergraphs[j];
for (k = 0; k < fg->nb_outputs; k++) {
AVFilterInOut *out = fg->outputs[k]->out_tmp;
if (out && !strcmp(out->name, map->linklabel)) {
ofilter = fg->outputs[k];
goto loop_end;
}
}
}
loop_end:
if (!ofilter) {
av_log(NULL, AV_LOG_FATAL, "Output with label '%s' does not exist "
"in any defined filter graph, or was already used elsewhere.\n", map->linklabel);
exit_program(1);
}
init_output_filter(ofilter, o, oc);
} else {
int src_idx = input_files[map->file_index]->ist_index + map->stream_index;
ist = input_streams[input_files[map->file_index]->ist_index + map->stream_index];
if(o->subtitle_disable && ist->st->codec->codec_type == AVMEDIA_TYPE_SUBTITLE)
continue;
if(o-> audio_disable && ist->st->codec->codec_type == AVMEDIA_TYPE_AUDIO)
continue;
if(o-> video_disable && ist->st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
continue;
if(o-> data_disable && ist->st->codec->codec_type == AVMEDIA_TYPE_DATA)
continue;
ost = NULL;
switch (ist->st->codec->codec_type) {
case AVMEDIA_TYPE_VIDEO: ost = new_video_stream (o, oc, src_idx); break;
case AVMEDIA_TYPE_AUDIO: ost = new_audio_stream (o, oc, src_idx); break;
case AVMEDIA_TYPE_SUBTITLE: ost = new_subtitle_stream (o, oc, src_idx); break;
case AVMEDIA_TYPE_DATA: ost = new_data_stream (o, oc, src_idx); break;
case AVMEDIA_TYPE_ATTACHMENT: ost = new_attachment_stream(o, oc, src_idx); break;
case AVMEDIA_TYPE_UNKNOWN:
if (copy_unknown_streams) {
ost = new_unknown_stream (o, oc, src_idx);
break;
}
default:
av_log(NULL, ignore_unknown_streams ? AV_LOG_WARNING : AV_LOG_FATAL,
"Cannot map stream #%d:%d - unsupported type.\n",
map->file_index, map->stream_index);
if (!ignore_unknown_streams) {
av_log(NULL, AV_LOG_FATAL,
"If you want unsupported types ignored instead "
"of failing, please use the -ignore_unknown option\n"
"If you want them copied, please use -copy_unknown\n");
exit_program(1);
}
}
if (ost)
ost->sync_ist = input_streams[ input_files[map->sync_file_index]->ist_index
+ map->sync_stream_index];
}
}
}
/* handle attached files */
/*对应参数"attach"，添加一个附件到输出文件*/
for (i = 0; i < o->nb_attachments; i++) {
AVIOContext *pb;
uint8_t *attachment;
const char *p;
int64_t len;
if ((err = avio_open2(&pb, o->attachments[i], AVIO_FLAG_READ, &int_cb, NULL)) < 0) {
av_log(NULL, AV_LOG_FATAL, "Could not open attachment file %s.\n",
o->attachments[i]);
exit_program(1);
}
if ((len = avio_size(pb)) <= 0) {
av_log(NULL, AV_LOG_FATAL, "Could not get size of the attachment %s.\n",
o->attachments[i]);
exit_program(1);
}
if (!(attachment = av_malloc(len))) {
av_log(NULL, AV_LOG_FATAL, "Attachment %s too large to fit into memory.\n",
o->attachments[i]);
exit_program(1);
}
avio_read(pb, attachment, len);
ost = new_attachment_stream(o, oc, -1);
ost->stream_copy = 1;
ost->attachment_filename = o->attachments[i];
ost->finished = 1;
ost->st->codec->extradata = attachment;
ost->st->codec->extradata_size = len;
p = strrchr(o->attachments[i], '/');
av_dict_set(&ost->st->metadata, "filename", (p && *p) ? p + 1 : o->attachments[i], AV_DICT_DONT_OVERWRITE);
avio_closep(&pb);
}
for (i = nb_output_streams - oc->nb_streams; i < nb_output_streams; i++) { //for all streams of this output file
AVDictionaryEntry *e;
ost = output_streams[i];
if ((ost->stream_copy || ost->attachment_filename)
&& (e = av_dict_get(o->g->codec_opts, "flags", NULL, AV_DICT_IGNORE_SUFFIX))
&& (!e->key[5] || check_stream_specifier(oc, ost->st, e->key+6)))
if (av_opt_set(ost->st->codec, "flags", e->value, 0) < 0)
exit_program(1);
}
if (!oc->nb_streams && !(oc->oformat->flags & AVFMT_NOSTREAMS)) {
av_dump_format(oc, nb_output_files - 1, oc->filename, 1);
av_log(NULL, AV_LOG_ERROR, "Output file #%d does not contain any stream\n", nb_output_files - 1);
exit_program(1);
}
/* check if all codec options have been used */
unused_opts = strip_specifiers(o->g->codec_opts);
for (i = of->ost_index; i < nb_output_streams; i++) {
e = NULL;
while ((e = av_dict_get(output_streams[i]->encoder_opts, "", e,
AV_DICT_IGNORE_SUFFIX)))
av_dict_set(&unused_opts, e->key, NULL, 0);
}
e = NULL;
while ((e = av_dict_get(unused_opts, "", e, AV_DICT_IGNORE_SUFFIX))) {
const AVClass *class = avcodec_get_class();
const AVOption *option = av_opt_find(&class, e->key, NULL, 0,
AV_OPT_SEARCH_CHILDREN | AV_OPT_SEARCH_FAKE_OBJ);
const AVClass *fclass = avformat_get_class();
const AVOption *foption = av_opt_find(&fclass, e->key, NULL, 0,
AV_OPT_SEARCH_CHILDREN | AV_OPT_SEARCH_FAKE_OBJ);
if (!option || foption)
continue;
if (!(option->flags & AV_OPT_FLAG_ENCODING_PARAM)) {
av_log(NULL, AV_LOG_ERROR, "Codec AVOption %s (%s) specified for "
"output file #%d (%s) is not an encoding option.\n", e->key,
option->help ? option->help : "", nb_output_files - 1,
filename);
exit_program(1);
}
// gop_timecode is injected by generic code but not always used
if (!strcmp(e->key, "gop_timecode"))
continue;
av_log(NULL, AV_LOG_WARNING, "Codec AVOption %s (%s) specified for "
"output file #%d (%s) has not been used for any stream. The most "
"likely reason is either wrong type (e.g. a video option with "
"no video streams) or that it is a private option of some encoder "
"which was not actually used for any stream.\n", e->key,
option->help ? option->help : "", nb_output_files - 1, filename);
}
av_dict_free(&unused_opts);
/* set the encoding/decoding_needed flags */
for (i = of->ost_index; i < nb_output_streams; i++) {
OutputStream *ost = output_streams[i];
ost->encoding_needed = !ost->stream_copy;
if (ost->encoding_needed && ost->source_index >= 0) {
InputStream *ist = input_streams[ost->source_index];
ist->decoding_needed |= DECODING_FOR_OST;
}
}
/* check filename in case of an image number is expected */
if (oc->oformat->flags & AVFMT_NEEDNUMBER) {
if (!av_filename_number_test(oc->filename)) {
print_error(oc->filename, AVERROR(EINVAL));
exit_program(1);
}
}
if (!(oc->oformat->flags & AVFMT_NOSTREAMS) && !input_stream_potentially_available) {
av_log(NULL, AV_LOG_ERROR,
"No input streams but output needs an input stream\n");
exit_program(1);
}
if (!(oc->oformat->flags & AVFMT_NOFILE)) {
/* test if it already exists to avoid losing precious files */
assert_file_overwrite(filename);
/* open the file */
if ((err = avio_open2(&oc->pb, filename, AVIO_FLAG_WRITE,
&oc->interrupt_callback,
&of->opts)) < 0) {
print_error(filename, err);
exit_program(1);
}
} else if (strcmp(oc->oformat->name, "image2")==0 && !av_filename_number_test(filename))
assert_file_overwrite(filename);
if (o->mux_preload) {
av_dict_set_int(&of->opts, "preload", o->mux_preload*AV_TIME_BASE, 0);
}
oc->max_delay = (int)(o->mux_max_delay * AV_TIME_BASE);
/* copy metadata */
for (i = 0; i < o->nb_metadata_map; i++) {
char *p;
int in_file_index = strtol(o->metadata_map[i].u.str, &p, 0);
if (in_file_index >= nb_input_files) {
av_log(NULL, AV_LOG_FATAL, "Invalid input file index %d while processing metadata maps\n", in_file_index);
exit_program(1);
}
copy_metadata(o->metadata_map[i].specifier, *p ? p + 1 : p, oc,
in_file_index >= 0 ?
input_files[in_file_index]->ctx : NULL, o);
}
/* copy chapters */
if (o->chapters_input_file >= nb_input_files) {
if (o->chapters_input_file == INT_MAX) {
/* copy chapters from the first input file that has them*/
o->chapters_input_file = -1;
for (i = 0; i < nb_input_files; i++)
if (input_files[i]->ctx->nb_chapters) {
o->chapters_input_file = i;
break;
}
} else {
av_log(NULL, AV_LOG_FATAL, "Invalid input file index %d in chapter mapping.\n",
o->chapters_input_file);
exit_program(1);
}
}
if (o->chapters_input_file >= 0)
copy_chapters(input_files[o->chapters_input_file], of,
!o->metadata_chapters_manual);
/* copy global metadata by default */
if (!o->metadata_global_manual && nb_input_files){
av_dict_copy(&oc->metadata, input_files[0]->ctx->metadata,
AV_DICT_DONT_OVERWRITE);
if(o->recording_time != INT64_MAX)
av_dict_set(&oc->metadata, "duration", NULL, 0);
av_dict_set(&oc->metadata, "creation_time", NULL, 0);
}
if (!o->metadata_streams_manual)
for (i = of->ost_index; i < nb_output_streams; i++) {
InputStream *ist;
if (output_streams[i]->source_index < 0) /* this is true e.g. for attached files */
continue;
ist = input_streams[output_streams[i]->source_index];
av_dict_copy(&output_streams[i]->st->metadata, ist->st->metadata, AV_DICT_DONT_OVERWRITE);
if (!output_streams[i]->stream_copy) {
av_dict_set(&output_streams[i]->st->metadata, "encoder", NULL, 0);
if (ist->autorotate)
av_dict_set(&output_streams[i]->st->metadata, "rotate", NULL, 0);
}
}
/* process manually set programs */
for (i = 0; i < o->nb_program; i++) {
const char *p = o->program[i].u.str;
int progid = i+1;
AVProgram *program;
while(*p) {
const char *p2 = av_get_token(&p, ":");
const char *to_dealloc = p2;
char *key;
if (!p2)
break;
if(*p) p++;
key = av_get_token(&p2, "=");
if (!key || !*p2) {
av_freep(&to_dealloc);
av_freep(&key);
break;
}
p2++;
if (!strcmp(key, "program_num"))
progid = strtol(p2, NULL, 0);
av_freep(&to_dealloc);
av_freep(&key);
}
program = av_new_program(oc, progid);
p = o->program[i].u.str;
while(*p) {
const char *p2 = av_get_token(&p, ":");
const char *to_dealloc = p2;
char *key;
if (!p2)
break;
if(*p) p++;
key = av_get_token(&p2, "=");
if (!key) {
av_log(NULL, AV_LOG_FATAL,
"No '=' character in program string %s.\n",
p2);
exit_program(1);
}
if (!*p2)
exit_program(1);
p2++;
if (!strcmp(key, "title")) {
av_dict_set(&program->metadata, "title", p2, 0);
} else if (!strcmp(key, "program_num")) {
} else if (!strcmp(key, "st")) {
int st_num = strtol(p2, NULL, 0);
av_program_add_stream_index(oc, progid, st_num);
} else {
av_log(NULL, AV_LOG_FATAL, "Unknown program key %s.\n", key);
exit_program(1);
}
av_freep(&to_dealloc);
av_freep(&key);
}
}
/* process manually set metadata */
for (i = 0; i < o->nb_metadata; i++) {
AVDictionary **m;
char type, *val;
const char *stream_spec;
int index = 0, j, ret = 0;
val = strchr(o->metadata[i].u.str, '=');
if (!val) {
av_log(NULL, AV_LOG_FATAL, "No '=' character in metadata string %s.\n",
o->metadata[i].u.str);
exit_program(1);
}
*val++ = 0;
parse_meta_type(o->metadata[i].specifier, &type, &index, &stream_spec);
if (type == 's') {
for (j = 0; j < oc->nb_streams; j++) {
ost = output_streams[nb_output_streams - oc->nb_streams + j];
if ((ret = check_stream_specifier(oc, oc->streams[j], stream_spec)) > 0) {
av_dict_set(&oc->streams[j]->metadata, o->metadata[i].u.str, *val ? val : NULL, 0);
if (!strcmp(o->metadata[i].u.str, "rotate")) {
ost->rotate_overridden = 1;
}
} else if (ret < 0)
exit_program(1);
}
}
else {
switch (type) {
case 'g':
m = &oc->metadata;
break;
case 'c':
if (index < 0 || index >= oc->nb_chapters) {
av_log(NULL, AV_LOG_FATAL, "Invalid chapter index %d in metadata specifier.\n", index);
exit_program(1);
}
m = &oc->chapters[index]->metadata;
break;
case 'p':
if (index < 0 || index >= oc->nb_programs) {
av_log(NULL, AV_LOG_FATAL, "Invalid program index %d in metadata specifier.\n", index);
exit_program(1);
}
m = &oc->programs[index]->metadata;
break;
default:
av_log(NULL, AV_LOG_FATAL, "Invalid metadata specifier %s.\n", o->metadata[i].specifier);
exit_program(1);
}
av_dict_set(m, o->metadata[i].u.str, *val ? val : NULL, 0);
}
}
return 0;
}
new_video_stream()
static OutputStream *new_video_stream(OptionsContext *o, AVFormatContext *oc, int source_index)
{
AVStream *st;
OutputStream *ost;
AVCodecContext *video_enc;
char *frame_rate = NULL, *frame_aspect_ratio = NULL;
ost = new_output_stream(o, oc, AVMEDIA_TYPE_VIDEO, source_index);//在后面有详细说明
st = ost->st;
video_enc = ost->enc_ctx;
//对应参数"r"，设置帧率
MATCH_PER_STREAM_OPT(frame_rates, str, frame_rate, oc, st);
if (frame_rate && av_parse_video_rate(&ost->frame_rate, frame_rate) < 0) {
av_log(NULL, AV_LOG_FATAL, "Invalid framerate value: %s\n", frame_rate);
exit_program(1);
}
/*对应参数"vsync" -vsync ["cfr", "vfr", "passthrough", "drop"]
或者-vsync 0
#define VSYNC_AUTO -1
#define VSYNC_PASSTHROUGH 0
#define VSYNC_CFR 1
#define VSYNC_VFR 2
#define VSYNC_VSCFR 0xfe
#define VSYNC_DROP 0xff
*/
if (frame_rate && video_sync_method == VSYNC_PASSTHROUGH)
av_log(NULL, AV_LOG_ERROR, "Using -vsync 0 and -r can produce invalid output files\n");
//对应参数"aspect"，设置指定的显示比例
/*aspect可以是浮点数字的字符串，或一个字符串的比值，比值分别是纵横比的分子和分母。
For example "4:3", "16:9", "1.3333", and "1.7777" are valid argument values.*/
MATCH_PER_STREAM_OPT(frame_aspect_ratios, str, frame_aspect_ratio, oc, st);
if (frame_aspect_ratio) {
AVRational q;
if (av_parse_ratio(&q, frame_aspect_ratio, 255, 0, NULL) < 0 ||
q.num <= 0 || q.den <= 0) {
av_log(NULL, AV_LOG_FATAL, "Invalid aspect ratio: %s\n", frame_aspect_ratio);
exit_program(1);
}
ost->frame_aspect_ratio = q;
}
//对应参数"filter_script"和"filter"
MATCH_PER_STREAM_OPT(filter_scripts, str, ost->filters_script, oc, st);
MATCH_PER_STREAM_OPT(filters, str, ost->filters, oc, st);
if (!ost->stream_copy) {
const char *p = NULL;
char *frame_size = NULL;
char *frame_pix_fmt = NULL;
char *intra_matrix = NULL, *inter_matrix = NULL;
char *chroma_intra_matrix = NULL;
int do_pass = 0;
int i;
//对应参数"s"，设置宽高
MATCH_PER_STREAM_OPT(frame_sizes, str, frame_size, oc, st);
if (frame_size && av_parse_video_size(&video_enc->width, &video_enc->height, frame_size) < 0) {
av_log(NULL, AV_LOG_FATAL, "Invalid frame size: %s.\n", frame_size);
exit_program(1);
}
//frame_bits_per_raw_sample对应参数"bits_per_raw_sample"
/*"set the number of bits per raw sample"*/
video_enc->bits_per_raw_sample = frame_bits_per_raw_sample;
//对应参数"pix_fmt"，设置像素格式
MATCH_PER_STREAM_OPT(frame_pix_fmts, str, frame_pix_fmt, oc, st);
if (frame_pix_fmt && *frame_pix_fmt == '+') {
ost->keep_pix_fmt = 1;
if (!*++frame_pix_fmt)
frame_pix_fmt = NULL;
}
if (frame_pix_fmt && (video_enc->pix_fmt = av_get_pix_fmt(frame_pix_fmt)) == AV_PIX_FMT_NONE) {
av_log(NULL, AV_LOG_FATAL, "Unknown pixel format requested: %s.\n", frame_pix_fmt);
exit_program(1);
}
st->sample_aspect_ratio = video_enc->sample_aspect_ratio;
//对应参数"intra"，“-g 1”，只有I帧
if (intra_only)
video_enc->gop_size = 0;
//对应参数"intra_matrix"
MATCH_PER_STREAM_OPT(intra_matrices, str, intra_matrix, oc, st);
if (intra_matrix) {
if (!(video_enc->intra_matrix = av_mallocz(sizeof(*video_enc->intra_matrix) * 64))) {
av_log(NULL, AV_LOG_FATAL, "Could not allocate memory for intra matrix.\n");
exit_program(1);
}
parse_matrix_coeffs(video_enc->intra_matrix, intra_matrix);
}
//对应参数"chroma_intra_matrix"
MATCH_PER_STREAM_OPT(chroma_intra_matrices, str, chroma_intra_matrix, oc, st);
if (chroma_intra_matrix) {
uint16_t *p = av_mallocz(sizeof(*video_enc->chroma_intra_matrix) * 64);
if (!p) {
av_log(NULL, AV_LOG_FATAL, "Could not allocate memory for intra matrix.\n");
exit_program(1);
}
av_codec_set_chroma_intra_matrix(video_enc, p);
parse_matrix_coeffs(p, chroma_intra_matrix);
}
//对应参数"inter_matrix"
MATCH_PER_STREAM_OPT(inter_matrices, str, inter_matrix, oc, st);
if (inter_matrix) {
if (!(video_enc->inter_matrix = av_mallocz(sizeof(*video_enc->inter_matrix) * 64))) {
av_log(NULL, AV_LOG_FATAL, "Could not allocate memory for inter matrix.\n");
exit_program(1);
}
parse_matrix_coeffs(video_enc->inter_matrix, inter_matrix);
}
//对应参数"rc_override"
/*-rc_override[:stream_specifier] override (output,per-stream)
速率控制，覆盖指定的时间间隔，以'逗号分隔的int,int,int'列表格式。
前两个值是开始和结束的帧号，最后一个如果是整数，表示用量。如果是负数表示品质因素*/
MATCH_PER_STREAM_OPT(rc_overrides, str, p, oc, st);
for (i = 0; p; i++) {
int start, end, q;
int e = sscanf(p, "%d,%d,%d", &start, &end, &q);
if (e != 3) {
av_log(NULL, AV_LOG_FATAL, "error parsing rc_override\n");
exit_program(1);
}
video_enc->rc_override =
av_realloc_array(video_enc->rc_override,
i + 1, sizeof(RcOverride));
if (!video_enc->rc_override) {
av_log(NULL, AV_LOG_FATAL, "Could not (re)allocate memory for rc_override.\n");
exit_program(1);
}
video_enc->rc_override[i].start_frame = start;
video_enc->rc_override[i].end_frame = end;
if (q > 0) {
video_enc->rc_override[i].qscale = q;
video_enc->rc_override[i].quality_factor = 1.0;
}
else {
video_enc->rc_override[i].qscale = 0;
video_enc->rc_override[i].quality_factor = -q/100.0;
}
p = strchr(p, '/');
if (p) p++;
}
video_enc->rc_override_count = i;
//对应参数"psnr"，计算压缩的帧PSNR，表示视频的质量
if (do_psnr)
video_enc->flags|= AV_CODEC_FLAG_PSNR;
/* two pass mode 对应参数"pass" select the pass number (1 to 3)*/
MATCH_PER_STREAM_OPT(pass, i, do_pass, oc, st);
if (do_pass) {
if (do_pass & 1) {
video_enc->flags |= AV_CODEC_FLAG_PASS1;
av_dict_set(&ost->encoder_opts, "flags", "+pass1", AV_DICT_APPEND);
}
if (do_pass & 2) {
video_enc->flags |= AV_CODEC_FLAG_PASS2;
av_dict_set(&ost->encoder_opts, "flags", "+pass2", AV_DICT_APPEND);
}
}
//对应参数“passlogfile”
MATCH_PER_STREAM_OPT(passlogfiles, str, ost->logfile_prefix, oc, st);
if (ost->logfile_prefix &&
!(ost->logfile_prefix = av_strdup(ost->logfile_prefix)))
exit_program(1);
if (do_pass) {
char logfilename[1024];
FILE *f;
snprintf(logfilename, sizeof(logfilename), "%s-%d.log",
ost->logfile_prefix ? ost->logfile_prefix :
DEFAULT_PASS_LOGFILENAME_PREFIX,
i);
if (!strcmp(ost->enc->name, "libx264")) {
av_dict_set(&ost->encoder_opts, "stats", logfilename, AV_DICT_DONT_OVERWRITE);
} else {
if (video_enc->flags & AV_CODEC_FLAG_PASS2) {
char *logbuffer = read_file(logfilename);
if (!logbuffer) {
av_log(NULL, AV_LOG_FATAL, "Error reading log file '%s' for pass-2 encoding\n",
logfilename);
exit_program(1);
}
video_enc->stats_in = logbuffer;
}
if (video_enc->flags & AV_CODEC_FLAG_PASS1) {
f = av_fopen_utf8(logfilename, "wb");
if (!f) {
av_log(NULL, AV_LOG_FATAL,
"Cannot write log file '%s' for pass-1 encoding: %s\n",
logfilename, strerror(errno));
exit_program(1);
}
ost->logfile = f;
}
}
}
//对应参数"force_key_frames"，
/*
‘-force_key_frames[:stream_specifier] time[,time...] (output,per-stream)’
‘-force_key_frames[:stream_specifier] expr:expr (output,per-stream)’在指定的时间戳强制关键帧
*/
MATCH_PER_STREAM_OPT(forced_key_frames, str, ost->forced_keyframes, oc, st);
if (ost->forced_keyframes)
ost->forced_keyframes = av_strdup(ost->forced_keyframes);
//对应参数"force_fps"，强制设置视频帧率
MATCH_PER_STREAM_OPT(force_fps, i, ost->force_fps, oc, st);
//对应参数"top"
ost->top_field_first = -1;
MATCH_PER_STREAM_OPT(top_field_first, i, ost->top_field_first, oc, st);
//返回ost->filters_script或ost->filters，如果命令行都没，视频就返回"null" ，音频就返回 "anull"
ost->avfilter = get_ost_filters(o, oc, ost);
if (!ost->avfilter)
exit_program(1);
} else {
//流拷贝，不需要重新编码的处理
//对应参数"copyinkf"，复制初始非关键帧
MATCH_PER_STREAM_OPT(copy_initial_nonkeyframes, i, ost->copy_initial_nonkeyframes, oc ,st);
}
//如果是流拷贝，但是设置了"filter_script"或"filter"，就退出程序
if (ost->stream_copy)
check_streamcopy_filters(o, oc, ost, AVMEDIA_TYPE_VIDEO);
return ost;
}
new_output_stream()
1、为输出文件创建一路流
2、在output_streams链表中添加此路流
3、设置编码器信息
4、对命令行参数进行解析，并设置到ost中。
5、拷贝o->g 中的sws_dict, sws_dict, swr_opts, resample_opts，到ost的对应变量中
static OutputStream *new_output_stream(OptionsContext *o, AVFormatContext *oc, enum AVMediaType type, int source_index)
{
OutputStream *ost;
AVStream *st = avformat_new_stream(oc, NULL);//为输出文件创建一路流
int idx = oc->nb_streams - 1, ret = 0;
char *bsf = NULL, *next, *codec_tag = NULL;
AVBitStreamFilterContext *bsfc, *bsfc_prev = NULL;
double qscale = -1;
int i;
if (!st) {
av_log(NULL, AV_LOG_FATAL, "Could not alloc stream.\n");
exit_program(1);
}
//如果命令行有对"streamid"的设置做如下处理，它的含义是"set the value of an outfile streamid"
if (oc->nb_streams - 1 < o->nb_streamid_map)
st->id = o->streamid_map[oc->nb_streams - 1];
//为output_streams链表加一项。
GROW_ARRAY(output_streams, nb_output_streams);
if (!(ost = av_mallocz(sizeof(*ost))))
exit_program(1);
output_streams[nb_output_streams - 1] = ost;
ost->file_index = nb_output_files - 1;//指明在output_files链表中的下标
ost->index = idx;//在本文件中流的索引下标
ost->st = st;
st->codec->codec_type = type;
choose_encoder(o, oc, ost);//设置编码器信息。ost->enc，ost->st->codec->codec_id
ost->enc_ctx = avcodec_alloc_context3(ost->enc);
if (!ost->enc_ctx) {
av_log(NULL, AV_LOG_ERROR, "Error allocating the encoding context.\n");
exit_program(1);
}
ost->enc_ctx->codec_type = type;
//由于filter_codec_opts()函数最后一个参数需要ost->enc，所以分为两支
if (ost->enc) {
AVIOContext *s = NULL;
char *buf = NULL, *arg = NULL, *preset = NULL;
//过滤出视频编码需要的参数来
ost->encoder_opts = filter_codec_opts(o->g->codec_opts, ost->enc->id, oc, st, ost->enc);
//参考[两个常用的宏定义]，对应的参数是"pre"，目前不清楚
MATCH_PER_STREAM_OPT(presets, str, preset, oc, st);
if (preset && (!(ret = get_preset_file_2(preset, ost->enc->name, &s)))) {
do {
buf = get_line(s);
if (!buf[0] || buf[0] == '#') {
av_free(buf);
continue;
}
if (!(arg = strchr(buf, '='))) {
av_log(NULL, AV_LOG_FATAL, "Invalid line found in the preset file.\n");
exit_program(1);
}
*arg++ = 0;
av_dict_set(&ost->encoder_opts, buf, arg, AV_DICT_DONT_OVERWRITE);
av_free(buf);
} while (!s->eof_reached);
avio_closep(&s);
}
if (ret) {
av_log(NULL, AV_LOG_FATAL,
"Preset %s specified for stream %d:%d, but could not be opened.\n",
preset, ost->file_index, ost->index);
exit_program(1);
}
} else {
ost->encoder_opts = filter_codec_opts(o->g->codec_opts, AV_CODEC_ID_NONE, oc, st, NULL);
}
//对应参数"frames"，"vframes"，设置输出的帧数。
ost->max_frames = INT64_MAX;
MATCH_PER_STREAM_OPT(max_frames, i64, ost->max_frames, oc, st);
for (i = 0; i<o->nb_max_frames; i++) {
char *p = o->max_frames[i].specifier;
if (!*p && type != AVMEDIA_TYPE_VIDEO) {
av_log(NULL, AV_LOG_WARNING, "Applying unspecific -frames to non video streams, maybe you meant -vframes ?\n");
break;
}
}
//对应参数"copypriorss"，"copy or discard frames before start time"
ost->copy_prior_start = -1;
MATCH_PER_STREAM_OPT(copy_prior_start, i, ost->copy_prior_start, oc ,st);
//对应参数"bsf"，"absf"，"vbsf"
MATCH_PER_STREAM_OPT(bitstream_filters, str, bsf, oc, st);
while (bsf) {
char *arg = NULL;
if (next = strchr(bsf, ','))
*next++ = 0;
if (arg = strchr(bsf, '='))
*arg++ = 0;
if (!(bsfc = av_bitstream_filter_init(bsf))) {
av_log(NULL, AV_LOG_FATAL, "Unknown bitstream filter %s\n", bsf);
exit_program(1);
}
if (bsfc_prev)
bsfc_prev->next = bsfc;
else
ost->bitstream_filters = bsfc;
if (arg)
if (!(bsfc->args = av_strdup(arg))) {
av_log(NULL, AV_LOG_FATAL, "Bitstream filter memory allocation failed\n");
exit_program(1);
}
bsfc_prev = bsfc;
bsf = next;
}
//对应参数"tag"
MATCH_PER_STREAM_OPT(codec_tags, str, codec_tag, oc, st);
if (codec_tag) {
uint32_t tag = strtol(codec_tag, &next, 0);
if (*next)
tag = AV_RL32(codec_tag);
ost->st->codec->codec_tag =
ost->enc_ctx->codec_tag = tag;
}
//对应参数"qscale:[v:a:s:d]"/"q" 以<数值>质量为基础的VBR，取值0.01-255，约小质量越好
MATCH_PER_STREAM_OPT(qscale, dbl, qscale, oc, st);
if (qscale >= 0) {
ost->enc_ctx->flags |= AV_CODEC_FLAG_QSCALE;
ost->enc_ctx->global_quality = FF_QP2LAMBDA * qscale;
}
//对应参数"disposition"
MATCH_PER_STREAM_OPT(disposition, str, ost->disposition, oc, st);
ost->disposition = av_strdup(ost->disposition);
//Place global headers in extradata instead of every keyframe
if (oc->oformat->flags & AVFMT_GLOBALHEADER)
ost->enc_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
av_dict_copy(&ost->sws_dict, o->g->sws_dict, 0);
av_dict_copy(&ost->swr_opts, o->g->swr_opts, 0);
if (ost->enc && av_get_exact_bits_per_sample(ost->enc->id) == 24)
av_dict_set(&ost->swr_opts, "output_sample_bits", "24", 0);
av_dict_copy(&ost->resample_opts, o->g->resample_opts, 0);
ost->source_index = source_index;
if (source_index >= 0) {
ost->sync_ist = input_streams[source_index];
input_streams[source_index]->discard = 0;
input_streams[source_index]->st->discard = input_streams[source_index]->user_set_discard;
}
ost->last_mux_dts = AV_NOPTS_VALUE;
return ost;
}
choose_encoder()
主要设置两个值
1、ost->enc
2、ost->st->codec->codec_id
或者ost->stream_copy（如果不改变编码格式时设为1）
static void choose_encoder(OptionsContext *o, AVFormatContext *s, OutputStream *ost)
{
char *codec_name = NULL;
//找是否在o中有针对输出流的格式定义。
MATCH_PER_STREAM_OPT(codec_names, str, codec_name, s, ost->st);
if (!codec_name) {
//没传入参数的时候做如下处理，先根据文件名猜编码
ost->st->codec->codec_id = av_guess_codec(s->oformat, NULL, s->filename,
NULL, ost->st->codec->codec_type);
ost->enc = avcodec_find_encoder(ost->st->codec->codec_id);
} else if (!strcmp(codec_name, "copy"))
ost->stream_copy = 1;
else {
//命令行中有定义。如：-c:v h264
ost->enc = find_codec_or_die(codec_name, ost->st->codec->codec_type, 1);
ost->st->codec->codec_id = ost->enc->id;
}
}
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