从头用脚分析FFmpeg源码 - avcodec_open2
奚高扬
avcodec_open2 作用
按照惯例，看FFmpeg的解释
/**
* Initialize the AVCodecContext to use the given AVCodec. Prior to using this
* function the context has to be allocated with avcodec_alloc_context3().
*
* The functions avcodec_find_decoder_by_name(), avcodec_find_encoder_by_name(),
* avcodec_find_decoder() and avcodec_find_encoder() provide an easy way for
* retrieving a codec.
*
* @warning This function is not thread safe!
*
* @note Always call this function before using decoding routines (such as
* @ref avcodec_receive_frame()).
*
* @code
* av_dict_set(&opts, "b", "2.5M", 0);
* codec = avcodec_find_decoder(AV_CODEC_ID_H264);
* if (!codec)
* exit(1);
*
* context = avcodec_alloc_context3(codec);
*
* if (avcodec_open2(context, codec, opts) < 0)
* exit(1);
* @endcode
*
* @param avctx The context to initialize.
* @param codec The codec to open this context for. If a non-NULL codec has been
* previously passed to avcodec_alloc_context3() or
* for this context, then this parameter MUST be either NULL or
* equal to the previously passed codec.
* @param options A dictionary filled with AVCodecContext and codec-private options.
* On return this object will be filled with options that were not found.
*
* @return zero on success, a negative value on error
* @see avcodec_alloc_context3(), avcodec_find_decoder(), avcodec_find_encoder(),
* av_dict_set(), av_opt_find().
*/
int avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options);
这个函数就是根据给定的AVCodec，初始化AVCodecContext。
avcodec_open2源码
代码贼多，和avformat_find_stream_info有的一拼，但实际上没干很多东西，基本都是在malloc然后check，需要注意的就是多线程编码。
int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options)
{
int ret = 0;
int codec_init_ok = 0;
AVDictionary *tmp = NULL;
AVCodecInternal *avci;
//判断是否已经open了
if (avcodec_is_open(avctx))
return 0;
//下面这三个判断是判断有没有调用过avcodec_alloc_context3， 调用
//avcodec_alloc_context3的时候，传入的codec是否和现在的传入的
//codec是同一个（直接用avctx->codec中的不就得了，不知道为啥多次一举）
if (!codec && !avctx->codec) {
av_log(avctx, AV_LOG_ERROR, "No codec provided to avcodec_open2()\n");
return AVERROR(EINVAL);
}
if (codec && avctx->codec && codec != avctx->codec) {
av_log(avctx, AV_LOG_ERROR, "This AVCodecContext was allocated for %s, "
"but %s passed to avcodec_open2()\n", avctx->codec->name, codec->name);
return AVERROR(EINVAL);
}
if (!codec)
codec = avctx->codec;
if (avctx->extradata_size < 0 || avctx->extradata_size >= FF_MAX_EXTRADATA_SIZE)
return AVERROR(EINVAL);
if (options)
av_dict_copy(&tmp, *options, 0);
lock_avcodec(codec);
// malloc一些内置变量，在之后编解码阶段要使用
avci = av_mallocz(sizeof(*avci));
if (!avci) {
ret = AVERROR(ENOMEM);
goto end;
}
avctx->internal = avci;
#if FF_API_OLD_ENCDEC
avci->to_free = av_frame_alloc();
avci->compat_decode_frame = av_frame_alloc();
avci->compat_encode_packet = av_packet_alloc();
if (!avci->to_free || !avci->compat_decode_frame || !avci->compat_encode_packet) {
ret = AVERROR(ENOMEM);
goto free_and_end;
}
#endif
avci->buffer_frame = av_frame_alloc();
avci->buffer_pkt = av_packet_alloc();
avci->es.in_frame = av_frame_alloc();
avci->ds.in_pkt = av_packet_alloc();
avci->last_pkt_props = av_packet_alloc();
avci->pkt_props = av_fifo_alloc(sizeof(*avci->last_pkt_props));
if (!avci->buffer_frame || !avci->buffer_pkt ||
!avci->es.in_frame || !avci->ds.in_pkt ||
!avci->last_pkt_props || !avci->pkt_props) {
ret = AVERROR(ENOMEM);
goto free_and_end;
}
avci->skip_samples_multiplier = 1;
// 再根据codec的上下文大小，初始化一片空间
if (codec->priv_data_size > 0) {
if (!avctx->priv_data) {
avctx->priv_data = av_mallocz(codec->priv_data_size);
if (!avctx->priv_data) {
ret = AVERROR(ENOMEM);
goto free_and_end;
}
if (codec->priv_class) {
*(const AVClass **)avctx->priv_data = codec->priv_class;
av_opt_set_defaults(avctx->priv_data);
}
}
if (codec->priv_class && (ret = av_opt_set_dict(avctx->priv_data, &tmp)) < 0)
goto free_and_end;
} else {
avctx->priv_data = NULL;
}
// 设置一些编解码选项
if ((ret = av_opt_set_dict(avctx, &tmp)) < 0)
goto free_and_end;
if (avctx->codec_whitelist && av_match_list(codec->name, avctx->codec_whitelist, ',') <= 0) {
av_log(avctx, AV_LOG_ERROR, "Codec (%s) not on whitelist \'%s\'\n", codec->name, avctx->codec_whitelist);
ret = AVERROR(EINVAL);
goto free_and_end;
}
// only call ff_set_dimensions() for non H.264/VP6F/DXV codecs so as not to overwrite previously setup dimensions
// 宽高检查
if (!(avctx->coded_width && avctx->coded_height && avctx->width && avctx->height &&
(avctx->codec_id == AV_CODEC_ID_H264 || avctx->codec_id == AV_CODEC_ID_VP6F || avctx->codec_id == AV_CODEC_ID_DXV))) {
//非H264的codec，这里面就大概是说，根据coded_width和像素类型以及一些其他的条件，计算出来width
//为什么这么做，还不咋清楚，只了解H.264的编码，所以这里暂时不管。
if (avctx->coded_width && avctx->coded_height)
ret = ff_set_dimensions(avctx, avctx->coded_width, avctx->coded_height);
else if (avctx->width && avctx->height)
ret = ff_set_dimensions(avctx, avctx->width, avctx->height);
if (ret < 0)
goto free_and_end;
}
//max_pixels默认是INT_MAX，是在调用avcodec_alloc_context3的时候初始化设置的
//也可以通过修改调用avcodec_alloc_context3时，传入的option来修改max_pixels
//这里也是判断宽高
if ((avctx->coded_width || avctx->coded_height || avctx->width || avctx->height)
&& ( av_image_check_size2(avctx->coded_width, avctx->coded_height, avctx->max_pixels, AV_PIX_FMT_NONE, 0, avctx) < 0
|| av_image_check_size2(avctx->width, avctx->height, avctx->max_pixels, AV_PIX_FMT_NONE, 0, avctx) < 0)) {
av_log(avctx, AV_LOG_WARNING, "Ignoring invalid width/height values\n");
ff_set_dimensions(avctx, 0, 0);
}
//判断宽高比
if (avctx->width > 0 && avctx->height > 0) {
if (av_image_check_sar(avctx->width, avctx->height,
avctx->sample_aspect_ratio) < 0) {
av_log(avctx, AV_LOG_WARNING, "ignoring invalid SAR: %u/%u\n",
avctx->sample_aspect_ratio.num,
avctx->sample_aspect_ratio.den);
avctx->sample_aspect_ratio = (AVRational){ 0, 1 };
}
}
//音频声道判断
if (avctx->channels > FF_SANE_NB_CHANNELS || avctx->channels < 0) {
av_log(avctx, AV_LOG_ERROR, "Too many or invalid channels: %d\n", avctx->channels);
ret = AVERROR(EINVAL);
goto free_and_end;
}
if (av_codec_is_decoder(codec) &&
codec->type == AVMEDIA_TYPE_AUDIO &&
!(codec->capabilities & AV_CODEC_CAP_CHANNEL_CONF) &&
avctx->channels == 0) {
av_log(avctx, AV_LOG_ERROR, "Decoder requires channel count but channels not set\n");
ret = AVERROR(EINVAL);
goto free_and_end;
}
//采样率判断
if (avctx->sample_rate < 0) {
av_log(avctx, AV_LOG_ERROR, "Invalid sample rate: %d\n", avctx->sample_rate);
ret = AVERROR(EINVAL);
goto free_and_end;
}
if (avctx->block_align < 0) {
av_log(avctx, AV_LOG_ERROR, "Invalid block align: %d\n", avctx->block_align);
ret = AVERROR(EINVAL);
goto free_and_end;
}
avctx->codec = codec;
if ((avctx->codec_type == AVMEDIA_TYPE_UNKNOWN || avctx->codec_type == codec->type) &&
avctx->codec_id == AV_CODEC_ID_NONE) {
avctx->codec_type = codec->type;
avctx->codec_id = codec->id;
}
if (avctx->codec_id != codec->id || (avctx->codec_type != codec->type
&& avctx->codec_type != AVMEDIA_TYPE_ATTACHMENT)) {
av_log(avctx, AV_LOG_ERROR, "Codec type or id mismatches\n");
ret = AVERROR(EINVAL);
goto free_and_end;
}
avctx->frame_number = 0;
avctx->codec_descriptor = avcodec_descriptor_get(avctx->codec_id);
//是否是试验性的编解码器
if ((avctx->codec->capabilities & AV_CODEC_CAP_EXPERIMENTAL) &&
avctx->strict_std_compliance > FF_COMPLIANCE_EXPERIMENTAL) {
const char *codec_string = av_codec_is_encoder(codec) ? "encoder" : "decoder";
const AVCodec *codec2;
av_log(avctx, AV_LOG_ERROR,
"The %s '%s' is experimental but experimental codecs are not enabled, "
"add '-strict %d' if you want to use it.\n",
codec_string, codec->name, FF_COMPLIANCE_EXPERIMENTAL);
codec2 = av_codec_is_encoder(codec) ? avcodec_find_encoder(codec->id) : avcodec_find_decoder(codec->id);
if (!(codec2->capabilities & AV_CODEC_CAP_EXPERIMENTAL))
av_log(avctx, AV_LOG_ERROR, "Alternatively use the non experimental %s '%s'.\n",
codec_string, codec2->name);
ret = AVERROR_EXPERIMENTAL;
goto free_and_end;
}
if (avctx->codec_type == AVMEDIA_TYPE_AUDIO &&
(!avctx->time_base.num || !avctx->time_base.den)) {
avctx->time_base.num = 1;
avctx->time_base.den = avctx->sample_rate;
}
//判断编解码器，然后各种判断参数是否正确。
//初始化一些变量
if (av_codec_is_encoder(avctx->codec))
ret = ff_encode_preinit(avctx);
else
ret = ff_decode_preinit(avctx);
if (ret < 0)
goto free_and_end;
if (!HAVE_THREADS)
av_log(avctx, AV_LOG_WARNING, "Warning: not compiled with thread support, using thread emulation\n");
//如果是编码器，可以创建多线程编码，ff_frame_thread_encoder_init会根据线程数量
//创建多个编码器上下文，然后多线程编码
// CONFIG_FRAME_THREAD_ENCODER是表示可以多线程编码，CONFIG_FRAME_THREAD_ENCODER的
// 前提就是HAVE_THREADS，之后详细解释一下ffmpeg configure的构建过程。
if (CONFIG_FRAME_THREAD_ENCODER && av_codec_is_encoder(avctx->codec)) {
unlock_avcodec(codec); //we will instantiate a few encoders thus kick the counter to prevent false detection of a problem
ret = ff_frame_thread_encoder_init(avctx, options ? *options : NULL);
lock_avcodec(codec);
if (ret < 0)
goto free_and_end;
}
// FF_THREAD_FRAME解码器多线程，ff_thread_init用于解码器多线程初始化
if (HAVE_THREADS
&& !(avci->frame_thread_encoder && (avctx->active_thread_type&FF_THREAD_FRAME))) {
ret = ff_thread_init(avctx);
if (ret < 0) {
goto free_and_end;
}
}
if (!HAVE_THREADS && !(codec->caps_internal & FF_CODEC_CAP_AUTO_THREADS))
avctx->thread_count = 1;
if ( avctx->codec->init && (!(avctx->active_thread_type&FF_THREAD_FRAME)
|| avci->frame_thread_encoder)) {
// 重头戏，编解码器的初始化，我们这里使用x264 或者ffmpeg自带的解码器
// avctx->active_thread_type&FF_THREAD_FRAME证明会在ff_thread_init中调用codec->init函数
ret = avctx->codec->init(avctx);
if (ret < 0) {
codec_init_ok = -1;
goto free_and_end;
}
codec_init_ok = 1;
}
ret=0;
//后面继续对解码器的一些参数进行判断。
if (av_codec_is_decoder(avctx->codec)) {
if (!avctx->bit_rate)
avctx->bit_rate = get_bit_rate(avctx);
/* validate channel layout from the decoder */
if (avctx->channel_layout) {
int channels = av_get_channel_layout_nb_channels(avctx->channel_layout);
if (!avctx->channels)
avctx->channels = channels;
else if (channels != avctx->channels) {
char buf[512];
av_get_channel_layout_string(buf, sizeof(buf), -1, avctx->channel_layout);
av_log(avctx, AV_LOG_WARNING,
"Channel layout '%s' with %d channels does not match specified number of channels %d: "
"ignoring specified channel layout\n",
buf, channels, avctx->channels);
avctx->channel_layout = 0;
}
}
if (avctx->channels && avctx->channels < 0 ||
avctx->channels > FF_SANE_NB_CHANNELS) {
ret = AVERROR(EINVAL);
goto free_and_end;
}
if (avctx->bits_per_coded_sample < 0) {
ret = AVERROR(EINVAL);
goto free_and_end;
}
if (avctx->sub_charenc) {
if (avctx->codec_type != AVMEDIA_TYPE_SUBTITLE) {
av_log(avctx, AV_LOG_ERROR, "Character encoding is only "
"supported with subtitles codecs\n");
ret = AVERROR(EINVAL);
goto free_and_end;
} else if (avctx->codec_descriptor->props & AV_CODEC_PROP_BITMAP_SUB) {
av_log(avctx, AV_LOG_WARNING, "Codec '%s' is bitmap-based, "
"subtitles character encoding will be ignored\n",
avctx->codec_descriptor->name);
avctx->sub_charenc_mode = FF_SUB_CHARENC_MODE_DO_NOTHING;
} else {
/* input character encoding is set for a text based subtitle
* codec at this point */
if (avctx->sub_charenc_mode == FF_SUB_CHARENC_MODE_AUTOMATIC)
avctx->sub_charenc_mode = FF_SUB_CHARENC_MODE_PRE_DECODER;
if (avctx->sub_charenc_mode == FF_SUB_CHARENC_MODE_PRE_DECODER) {
#if CONFIG_ICONV
iconv_t cd = iconv_open("UTF-8", avctx->sub_charenc);
if (cd == (iconv_t)-1) {
ret = AVERROR(errno);
av_log(avctx, AV_LOG_ERROR, "Unable to open iconv context "
"with input character encoding \"%s\"\n", avctx->sub_charenc);
goto free_and_end;
}
iconv_close(cd);
#else
av_log(avctx, AV_LOG_ERROR, "Character encoding subtitles "
"conversion needs a libavcodec built with iconv support "
"for this codec\n");
ret = AVERROR(ENOSYS);
goto free_and_end;
#endif
}
}
}
#if FF_API_AVCTX_TIMEBASE
if (avctx->framerate.num > 0 && avctx->framerate.den > 0)
avctx->time_base = av_inv_q(av_mul_q(avctx->framerate, (AVRational){avctx->ticks_per_frame, 1}));
#endif
}
if (codec->priv_data_size > 0 && avctx->priv_data && codec->priv_class) {
av_assert0(*(const AVClass **)avctx->priv_data == codec->priv_class);
}
end:
unlock_avcodec(codec);
if (options) {
av_dict_free(options);
*options = tmp;
}
return ret;
free_and_end:
if (avctx->codec && avctx->codec->close &&
(codec_init_ok > 0 || (codec_init_ok < 0 &&
avctx->codec->caps_internal & FF_CODEC_CAP_INIT_CLEANUP)))
avctx->codec->close(avctx);
if (HAVE_THREADS && avci->thread_ctx)
ff_thread_free(avctx);
if (codec->priv_class && avctx->priv_data)
av_opt_free(avctx->priv_data);
av_opt_free(avctx);
if (av_codec_is_encoder(avctx->codec)) {
#if FF_API_CODED_FRAME
FF_DISABLE_DEPRECATION_WARNINGS
av_frame_free(&avctx->coded_frame);
FF_ENABLE_DEPRECATION_WARNINGS
#endif
av_freep(&avctx->extradata);
avctx->extradata_size = 0;
}
av_dict_free(&tmp);
av_freep(&avctx->priv_data);
av_freep(&avctx->subtitle_header);
#if FF_API_OLD_ENCDEC
av_frame_free(&avci->to_free);
av_frame_free(&avci->compat_decode_frame);
av_packet_free(&avci->compat_encode_packet);
#endif
av_frame_free(&avci->buffer_frame);
av_packet_free(&avci->buffer_pkt);
av_packet_free(&avci->last_pkt_props);
av_fifo_freep(&avci->pkt_props);
av_packet_free(&avci->ds.in_pkt);
av_frame_free(&avci->es.in_frame);
av_bsf_free(&avci->bsf);
av_buffer_unref(&avci->pool);
av_freep(&avci);
avctx->internal = NULL;
avctx->codec = NULL;
goto end;
}
ff_frame_thread_encoder_init源码
就是多线程编码器的初始化，根据线程数量，创建对应数量的AVCodecContext。多线程编码就是在这里设置的，通过ThreadContext (avctx->internal->frame_thread_encoder) 作为多线程编码的上下文。
int ff_frame_thread_encoder_init(AVCodecContext *avctx, AVDictionary *options){
int i=0;
ThreadContext *c;
//这里都是一些检测选项，跳过
if( !(avctx->thread_type & FF_THREAD_FRAME)
|| !(avctx->codec->capabilities & AV_CODEC_CAP_FRAME_THREADS))
return 0;
if( !avctx->thread_count
&& avctx->codec_id == AV_CODEC_ID_MJPEG
&& !(avctx->flags & AV_CODEC_FLAG_QSCALE)) {
av_log(avctx, AV_LOG_DEBUG,
"Forcing thread count to 1 for MJPEG encoding, use -thread_type slice "
"or a constant quantizer if you want to use multiple cpu cores\n");
avctx->thread_count = 1;
}
if( avctx->thread_count > 1
&& avctx->codec_id == AV_CODEC_ID_MJPEG
&& !(avctx->flags & AV_CODEC_FLAG_QSCALE))
av_log(avctx, AV_LOG_WARNING,
"MJPEG CBR encoding works badly with frame multi-threading, consider "
"using -threads 1, -thread_type slice or a constant quantizer.\n");
if (avctx->codec_id == AV_CODEC_ID_HUFFYUV ||
avctx->codec_id == AV_CODEC_ID_FFVHUFF) {
int warn = 0;
int context_model = 0;
AVDictionaryEntry *con = av_dict_get(options, "context", NULL, AV_DICT_MATCH_CASE);
if (con && con->value)
context_model = atoi(con->value);
if (avctx->flags & AV_CODEC_FLAG_PASS1)
warn = 1;
else if(context_model > 0) {
AVDictionaryEntry *t = av_dict_get(options, "non_deterministic",
NULL, AV_DICT_MATCH_CASE);
warn = !t || !t->value || !atoi(t->value) ? 1 : 0;
}
// huffyuv does not support these with multiple frame threads currently
if (warn) {
av_log(avctx, AV_LOG_WARNING,
"Forcing thread count to 1 for huffyuv encoding with first pass or context 1\n");
avctx->thread_count = 1;
}
}
// 根据cpu核数创建线程数量
if(!avctx->thread_count) {
avctx->thread_count = av_cpu_count();
avctx->thread_count = FFMIN(avctx->thread_count, MAX_THREADS);
}
if(avctx->thread_count <= 1)
return 0;
if(avctx->thread_count > MAX_THREADS)
return AVERROR(EINVAL);
//初始化参数
av_assert0(!avctx->internal->frame_thread_encoder);
//关联起来
c = avctx->internal->frame_thread_encoder = av_mallocz(sizeof(ThreadContext));
if(!c)
return AVERROR(ENOMEM);
c->parent_avctx = avctx;
pthread_mutex_init(&c->task_fifo_mutex, NULL);
pthread_mutex_init(&c->finished_task_mutex, NULL);
pthread_mutex_init(&c->buffer_mutex, NULL);
pthread_cond_init(&c->task_fifo_cond, NULL);
pthread_cond_init(&c->finished_task_cond, NULL);
atomic_init(&c->exit, 0);
c->max_tasks = avctx->thread_count + 2;
for (unsigned i = 0; i < c->max_tasks; i++) {
if (!(c->tasks[i].indata = av_frame_alloc()) ||
!(c->tasks[i].outdata = av_packet_alloc()))
goto fail;
}
//根据线程数量创建对应的AVCodecContext。
for(i=0; i<avctx->thread_count ; i++){
AVDictionary *tmp = NULL;
int ret;
void *tmpv;
AVCodecContext *thread_avctx = avcodec_alloc_context3(avctx->codec);
if(!thread_avctx)
goto fail;
// copy一些原有的配置，codec相关的priv_data共用
tmpv = thread_avctx->priv_data;
*thread_avctx = *avctx;
ret = av_opt_copy(thread_avctx, avctx);
if (ret < 0)
goto fail;
thread_avctx->priv_data = tmpv;
thread_avctx->internal = NULL;
if (avctx->codec->priv_class) {
int ret = av_opt_copy(thread_avctx->priv_data, avctx->priv_data);
if (ret < 0)
goto fail;
} else if (avctx->codec->priv_data_size) {
memcpy(thread_avctx->priv_data, avctx->priv_data, avctx->codec->priv_data_size);
}
thread_avctx->thread_count = 1;
thread_avctx->active_thread_type &= ~FF_THREAD_FRAME;
av_dict_copy(&tmp, options, 0);
av_dict_set(&tmp, "threads", "1", 0);
//每次重新使用avcodec_open2来打开一个编码器，这时候强制线程数量为1
if(avcodec_open2(thread_avctx, avctx->codec, &tmp) < 0) {
av_dict_free(&tmp);
goto fail;
}
av_dict_free(&tmp);
av_assert0(!thread_avctx->internal->frame_thread_encoder);
thread_avctx->internal->frame_thread_encoder = c;
// 创建线程，每个线程都调用worker函数
if(pthread_create(&c->worker[i], NULL, worker, thread_avctx)) {
goto fail;
}
}
avctx->active_thread_type = FF_THREAD_FRAME;
return 0;
fail:
avctx->thread_count = i;
av_log(avctx, AV_LOG_ERROR, "ff_frame_thread_encoder_init failed\n");
ff_frame_thread_encoder_free(avctx);
return -1;
}
worker源码
worker线程函数，就是等待ThreadContext中的信号量，如果等到了，就判断当前唤醒的是否是自己这个task_index，如果唤醒的是自己这个task，就进行编码操作，编码用的来源frame和输出pkt，都是来自于ThreadContext的tasks数组中，如果不是就继续等待下一个信号量。
static void * attribute_align_arg worker(void *v){
AVCodecContext *avctx = v;
ThreadContext *c = avctx->internal->frame_thread_encoder;
while (!atomic_load(&c->exit)) {
int got_packet = 0, ret;
AVPacket *pkt;
AVFrame *frame;
Task *task;
unsigned task_index;
// 未进行编码的时候，就锁在这里
pthread_mutex_lock(&c->task_fifo_mutex);
//task是保存在ThreadContext的tasks数组中，如果是当前的task就不需要在while了
while (c->next_task_index == c->task_index || atomic_load(&c->exit)) {
if (atomic_load(&c->exit)) {
pthread_mutex_unlock(&c->task_fifo_mutex);
goto end;
}
//信号量来的时候解锁，然后while循环判断一下是不是当前的task
//等待的是task_fifo_cond信号量，这个会在ff_thread_video_encode_frame方法中sign
pthread_cond_wait(&c->task_fifo_cond, &c->task_fifo_mutex);
}
task_index = c->next_task_index;
//设置下次task_index
c->next_task_index = (c->next_task_index + 1) % c->max_tasks;
pthread_mutex_unlock(&c->task_fifo_mutex);
/* The main thread ensures that any two outstanding tasks have
* different indices, ergo each worker thread owns its element
* of c->tasks with the exception of finished, which is shared
* with the main thread and guarded by finished_task_mutex. */
task = &c->tasks[task_index];//当前的task
frame = task->indata;
pkt = task->outdata;//设置输出pkt
// 每次从task中获得frame，然后调用编码方法。
ret = avctx->codec->encode2(avctx, pkt, frame, &got_packet);
if(got_packet) {
int ret2 = av_packet_make_refcounted(pkt);
if (ret >= 0 && ret2 < 0)
ret = ret2;
pkt->pts = pkt->dts = frame->pts;
} else {
pkt->data = NULL;
pkt->size = 0;
}
pthread_mutex_lock(&c->buffer_mutex);
av_frame_unref(frame);
pthread_mutex_unlock(&c->buffer_mutex);
pthread_mutex_lock(&c->finished_task_mutex);
task->return_code = ret;
task->finished = 1;
//完成之后 sign finished_task_cond信号量，ff_thread_video_encode_frame函数中等待着这个信号量
pthread_cond_signal(&c->finished_task_cond);
pthread_mutex_unlock(&c->finished_task_mutex);
}
end:
pthread_mutex_lock(&c->buffer_mutex);
avcodec_close(avctx);
pthread_mutex_unlock(&c->buffer_mutex);
av_freep(&avctx);
return NULL;
}
ff_thread_init源码
初始化AVCodecContext的多线程，这里是初始化解码器多线程相关的参数和对应线程，编码器调用ff_frame_thread_encoder_init。
int ff_thread_init(AVCodecContext *avctx)
{
//根据codec的capabilities和avctx的flags设置avctx->active_thread_type
//看看支持什么样子的多线程，是帧级还是场级
validate_thread_parameters(avctx);
if (avctx->active_thread_type&FF_THREAD_SLICE)
//场级
return ff_slice_thread_init(avctx);
else if (avctx->active_thread_type&FF_THREAD_FRAME)
//帧级
return ff_frame_thread_init(avctx);
return 0;
}
ff_frame_thread_init 源码
帧级解码多线程初始化。
int ff_frame_thread_init(AVCodecContext *avctx)
{
int thread_count = avctx->thread_count;
const AVCodec *codec = avctx->codec;
AVCodecContext *src = avctx;
// 帧级编码的上下文FrameThreadContext
FrameThreadContext *fctx;
int err, i = 0;
//设置线程数量，默认线程数量是nb_cpus + 1
if (!thread_count) {
int nb_cpus = av_cpu_count();
// use number of cores + 1 as thread count if there is more than one
if (nb_cpus > 1)
thread_count = avctx->thread_count = FFMIN(nb_cpus + 1, MAX_AUTO_THREADS);
else
thread_count = avctx->thread_count = 1;
}
if (thread_count <= 1) {
avctx->active_thread_type = 0;
return 0;
}
avctx->internal->thread_ctx = fctx = av_mallocz(sizeof(FrameThreadContext));
if (!fctx)
return AVERROR(ENOMEM);
// 初始化fctx中的锁和信号量
err = init_pthread(fctx, thread_ctx_offsets);
if (err < 0) {
free_pthread(fctx, thread_ctx_offsets);
av_freep(&avctx->internal->thread_ctx);
return err;
}
fctx->async_lock = 1;
fctx->delaying = 1;
if (codec->type == AVMEDIA_TYPE_VIDEO)
avctx->delay = src->thread_count - 1;
// 多个线程，PerThreadContext结构体中有pthread_t
fctx->threads = av_mallocz_array(thread_count, sizeof(PerThreadContext));
if (!fctx->threads) {
err = AVERROR(ENOMEM);
goto error;
}
for (; i < thread_count; ) {
PerThreadContext *p = &fctx->threads[i];
int first = !i;
//初始化PerThreadContext，也初始化对应的线程
err = init_thread(p, &i, fctx, avctx, src, codec, first);
if (err < 0)
goto error;
}
return 0;
error:
ff_frame_thread_free(avctx, i);
return err;
}
init_thread源码
初始化PerThreadContext中的线程，包括其中的一些锁，信号量，frame等
static av_cold int init_thread(PerThreadContext *p, int *threads_to_free,
FrameThreadContext *fctx, AVCodecContext *avctx,
AVCodecContext *src, const AVCodec *codec, int first)
{
AVCodecContext *copy;
int err;
// 下面大部分都是初始化一些参数
atomic_init(&p->state, STATE_INPUT_READY);
copy = av_memdup(src, sizeof(*src));
if (!copy)
return AVERROR(ENOMEM);
copy->priv_data = NULL;
/* From now on, this PerThreadContext will be cleaned up by
* ff_frame_thread_free in case of errors. */
(*threads_to_free)++;
p->parent = fctx;
p->avctx = copy;
copy->internal = av_memdup(src->internal, sizeof(*src->internal));
if (!copy->internal)
return AVERROR(ENOMEM);
copy->internal->thread_ctx = p;
copy->delay = avctx->delay;
if (codec->priv_data_size) {
copy->priv_data = av_mallocz(codec->priv_data_size);
if (!copy->priv_data)
return AVERROR(ENOMEM);
if (codec->priv_class) {
*(const AVClass **)copy->priv_data = codec->priv_class;
err = av_opt_copy(copy->priv_data, src->priv_data);
if (err < 0)
return err;
}
}
//这里是初始化PerThreadContext中的锁和信号量
err = init_pthread(p, per_thread_offsets);
if (err < 0)
return err;
if (!(p->frame = av_frame_alloc()) ||
!(p->avpkt = av_packet_alloc()))
return AVERROR(ENOMEM);
copy->internal->last_pkt_props = p->avpkt;
if (!first)
copy->internal->is_copy = 1;
// 多线程解码器会在这里调用对应codec的init方法，所以在avcodec_open2函数中，
// 会先判断avctx->internal->thread_ctx是否为null
if (codec->init) {
err = codec->init(copy);
if (err < 0) {
if (codec->caps_internal & FF_CODEC_CAP_INIT_CLEANUP)
p->thread_init = NEEDS_CLOSE;
return err;
}
}
p->thread_init = NEEDS_CLOSE;
if (first)
update_context_from_thread(avctx, copy, 1);
atomic_init(&p->debug_threads, (copy->debug & FF_DEBUG_THREADS) != 0);
// 初始化线程，线程函数为frame_worker_thread
err = AVERROR(pthread_create(&p->thread, NULL, frame_worker_thread, p));
if (err < 0)
return err;
p->thread_init = INITIALIZED;
return 0;
}
frame_worker_thread 源码
frame_worker_thread是具体的解码线程，里面会调用解码函数。
简单来讲，等待PerThreadContext中的input_cond信号量，等到之后调用codec->decode函数解码。等解码完成之后调用output_cond信号量。
/**
* Codec worker thread.
*
* Automatically calls ff_thread_finish_setup() if the codec does
* not provide an update_thread_context method, or if the codec returns
* before calling it.
*/
static attribute_align_arg void *frame_worker_thread(void *arg)
{
PerThreadContext *p = arg;
AVCodecContext *avctx = p->avctx;
const AVCodec *codec = avctx->codec;
pthread_mutex_lock(&p->mutex);
while (1) {
// 等待input_cond信号量
while (atomic_load(&p->state) == STATE_INPUT_READY && !p->die)
pthread_cond_wait(&p->input_cond, &p->mutex);
if (p->die) break;
FF_DISABLE_DEPRECATION_WARNINGS
if (!codec->update_thread_context
#if FF_API_THREAD_SAFE_CALLBACKS
&& THREAD_SAFE_CALLBACKS(avctx)
#endif
)
ff_thread_finish_setup(avctx);
FF_ENABLE_DEPRECATION_WARNINGS
/* If a decoder supports hwaccel, then it must call ff_get_format().
* Since that call must happen before ff_thread_finish_setup(), the
* decoder is required to implement update_thread_context() and call
* ff_thread_finish_setup() manually. Therefore the above
* ff_thread_finish_setup() call did not happen and hwaccel_serializing
* cannot be true here. */
av_assert0(!p->hwaccel_serializing);
/* if the previous thread uses hwaccel then we take the lock to ensure
* the threads don't run concurrently */
if (avctx->hwaccel) {
pthread_mutex_lock(&p->parent->hwaccel_mutex);
p->hwaccel_serializing = 1;
}
av_frame_unref(p->frame);
p->got_frame = 0;
// 调用解码方法，参数是在PerThreadContext中来的。
p->result = codec->decode(avctx, p->frame, &p->got_frame, p->avpkt);
if ((p->result < 0 || !p->got_frame) && p->frame->buf[0]) {
if (avctx->codec->caps_internal & FF_CODEC_CAP_ALLOCATE_PROGRESS)
av_log(avctx, AV_LOG_ERROR, "A frame threaded decoder did not "
"free the frame on failure. This is a bug, please report it.\n");
av_frame_unref(p->frame);
}
if (atomic_load(&p->state) == STATE_SETTING_UP)
ff_thread_finish_setup(avctx);
if (p->hwaccel_serializing) {
p->hwaccel_serializing = 0;
pthread_mutex_unlock(&p->parent->hwaccel_mutex);
}
if (p->async_serializing) {
p->async_serializing = 0;
async_unlock(p->parent);
}
pthread_mutex_lock(&p->progress_mutex);
atomic_store(&p->state, STATE_INPUT_READY);
pthread_cond_broadcast(&p->progress_cond);
pthread_cond_signal(&p->output_cond);
pthread_mutex_unlock(&p->progress_mutex);
}
pthread_mutex_unlock(&p->mutex);
return NULL;
}
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