FFmepg 多线程解码历程
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FFmepg 多线程解码历程
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FFmepg 多線程解碼歷程 - 1:validate_thread_parameters
/**
?* Set the threading algorithms used.//設置線程的使用算法
?* Threading requires more than one thread.//需要一個以上的線程
?* Frame threading requires entire frames to be passed to the codec,//幀線程需要整個幀被傳遞到編碼解碼器
?* and introduces extra decoding delay, so is incompatible with low_delay.// 并引入了額外的解碼延遲，所以是不符合low_delay
?* @param avctx The context.
?*/
?//有效的線程參數
static void validate_thread_parameters(AVCodecContext *avctx)
{
??? //實現幀線程支持，需要在配置codec的時候設置codec的capabilities，flags，flags2
??? int frame_threading_supported = (avctx->codec->capabilities & CODEC_CAP_FRAME_THREADS)
??????????????????????????????? && !(avctx->flags & CODEC_FLAG_TRUNCATED)
??????????????????????????????? && !(avctx->flags & CODEC_FLAG_LOW_DELAY)
??????????????????????????????? && !(avctx->flags2 & CODEC_FLAG2_CHUNKS);
??? if (avctx->thread_count == 1) {??? //多線程要在雙核以上的機器上才行
??????? avctx->active_thread_type = 0;
??? } else if (frame_threading_supported && (avctx->thread_type & FF_THREAD_FRAME)) {//? 在codec初始化的時候設置avctx->thread_type |=FF_THREAD_FRAME
??????? avctx->active_thread_type = FF_THREAD_FRAME;?? //線程的類型設置為幀并行
??? } else if (avctx->codec->capabilities & CODEC_CAP_SLICE_THREADS &&
?????????????? avctx->thread_type & FF_THREAD_SLICE) {? //同樣的要實現片級并行則需要在codec初始化的時候設置條件
??????? avctx->active_thread_type = FF_THREAD_SLICE;
??? } else if (!(avctx->codec->capabilities & CODEC_CAP_AUTO_THREADS)) {
??????? avctx->thread_count?????? = 1;
??????? avctx->active_thread_type = 0;
??? }
??? if (avctx->thread_count > MAX_AUTO_THREADS)
??????? av_log(avctx, AV_LOG_WARNING,
?????????????? "Application has requested %d threads. Using a thread count greater than %d is not recommended.\n",
?????????????? avctx->thread_count, MAX_AUTO_THREADS);
}
注釋：
如果不知到幀與片 可以查看之前的轉載文章? http://blog.csdn.net/jwzhangjie/article/details/8739139
FFmepg 多線程解碼歷程 - 2 :avcodec_decode_video2
//解碼函數
int attribute_align_arg avcodec_decode_video2(AVCodecContext *avctx, AVFrame *picture,
????????????????????????????????????????????? int *got_picture_ptr,????????????????????????????????????????????? const AVPacket *avpkt)
{
??? AVCodecInternal *avci = avctx->internal;
??? int ret;
??? // copy to ensure we do not change avpkt
??? AVPacket tmp = *avpkt;
??? if (avctx->codec->type != AVMEDIA_TYPE_VIDEO) {?? //如果不是視頻類型，則退出
??????? av_log(avctx, AV_LOG_ERROR, "Invalid media type for video\n");
??????? return AVERROR(EINVAL);
??? }
??? *got_picture_ptr = 0;? /
??? if ((avctx->coded_width || avctx->coded_height) && av_image_check_size(avctx->coded_width, avctx->coded_height, 0, avctx))
??????? return AVERROR(EINVAL);
??? avcodec_get_frame_defaults(picture);
??? if (!avctx->refcounted_frames)
??????? av_frame_unref(&avci->to_free);
//如果是幀并行解碼的話
//需要在codec初始化的時候設置codec->capabilities |= CODEC_CAP_DELAY，查看注釋，設置avctx->active_thread_type |= FF_THREAD_FRAME
??????? int did_split = av_packet_split_side_data(&tmp);
??????? apply_param_change(avctx, &tmp);
??????? avctx->pkt = &tmp;
//需要配置configure? --enable-pthreads(我現在最新的默認生成的config.h就是#define? HAVE_THREADS 1)? ,設置avctx->active_thread_type |= FF_THREAD_FRAME
??????????? ret = ff_thread_decode_frame(avctx, picture, got_picture_ptr,&tmp);//進入幀級并行解碼
??????? else {//進入單線程解碼
??????????? ret = avctx->codec->decode(avctx, picture, got_picture_ptr, &tmp);
??????????? picture->pkt_dts = avpkt->dts;
??????????? if(!avctx->has_b_frames){
??????????????? av_frame_set_pkt_pos(picture, avpkt->pos);
??????????? }
??????????? //FIXME these should be under if(!avctx->has_b_frames)
??????????? /* get_buffer is supposed to set frame parameters */
??????????? if (!(avctx->codec->capabilities & CODEC_CAP_DR1)) {
??????????????? if (!picture->sample_aspect_ratio.num)??? picture->sample_aspect_ratio = avctx->sample_aspect_ratio;
??????????????? if (!picture->width)????????????????????? picture->width?????????????? = avctx->width;
??????????????? if (!picture->height)???????????????????? picture->height????????????? = avctx->height;
??????????????? if (picture->format == AV_PIX_FMT_NONE)?? picture->format????????????? = avctx->pix_fmt;
??????????? }
??????? }
??????? add_metadata_from_side_data(avctx, picture);
??????? emms_c(); //needed to avoid an emms_c() call before every return;
??????? avctx->pkt = NULL;
??????? if (did_split) {
??????????? ff_packet_free_side_data(&tmp);
??????????? if(ret == tmp.size)
??????????????? ret = avpkt->size;
??????? }
??????? if (ret < 0 && picture->data[0])
??????????? av_frame_unref(picture);
??????? if (*got_picture_ptr) {
??????????? if (!avctx->refcounted_frames) {
??????????????? avci->to_free = *picture;
??????????????? avci->to_free.extended_data = avci->to_free.data;
??????????? }
??????????? avctx->frame_number++;
??????????? av_frame_set_best_effort_timestamp(picture,
?????????????????????????????????????????????? guess_correct_pts(avctx,
???????????????????????????????????????????????????????????????? picture->pkt_pts,
???????????????????????????????????????????????????????????????? picture->pkt_dts));
??????? }
??? } else
??????? ret = 0;
??? /* many decoders assign whole AVFrames, thus overwriting extended_data;
???? * make sure it's set correctly */
//許多解碼器分配整個的AVFrames ，從而覆蓋extended_data相關
??? picture->extended_data = picture->data;
??? return ret;
}
?
注釋：
/**
?* Encoder or decoder requires flushing with NULL input at the end in order to
?* give the complete and correct output.
?*
?* NOTE: If this flag is not set, the codec is guaranteed to never be fed with
?*?????? with NULL data. The user can still send NULL data to the public encode
?*?????? or decode function, but libavcodec will not pass it along to the codec
?*?????? unless this flag is set.
?*
?* Decoders:
?* The decoder has a non-zero delay and needs to be fed with avpkt->data=NULL,
?* avpkt->size=0 at the end to get the delayed data until the decoder no longer
?* returns frames.
?*
?* Encoders:
?* The encoder needs to be fed with NULL data at the end of encoding until the
?* encoder no longer returns data.
?*
?* NOTE: For encoders implementing the AVCodec.encode2() function, setting this
?*?????? flag also means that the encoder must set the pts and duration for
?*?????? each output packet. If this flag is not set, the pts and duration will
?*?????? be determined by libavcodec from the input frame.
?*/
#define CODEC_CAP_DELAY?????????? 0x0020
FFmepg 多線程解碼歷程 - 3: int ff_thread_decode_frame
//幀級解碼函數，在avcodec_open2的時候，就會判斷片還是幀解碼，分析見下一篇
int ff_thread_decode_frame(AVCodecContext *avctx,
?????????????????????????? AVFrame *picture, int *got_picture_ptr,?????????????????????????? AVPacket *avpkt)
{
??? FrameThreadContext *fctx = avctx->thread_opaque; //thread_opaque見注釋1
??? int finished = fctx->next_finished; //從返回結果輸出的下一個內容
??? PerThreadContext *p; //查看注釋2
??? int err;
??? /*
???? * Submit a packet to the next decoding thread.
*提交數據包發送到下一個解碼線程
??? p = &fctx->threads[fctx->next_decoding];
??? err = update_context_from_user(p->avctx, avctx); //將用戶提交的avctx復制到p->avctx里面
??? if (err) return err;
??? err = submit_packet(p, avpkt);
??? if (err) return err;
??? /*
???? * If we're still receiving the initial packets, don't return a frame.
???? *如果我們仍然接收的初步數據包，不返回幀
*/
??? if (fctx->delaying) {
??????? if (fctx->next_decoding >= (avctx->thread_count-1)) fctx->delaying = 0;
??????? *got_picture_ptr=0;
??????? if (avpkt->size)
??????????? return avpkt->size;
??? }
??? /*
???? * Return the next available frame from the oldest thread.//返回下一個可用幀從最早的線程
???? * If we're at the end of the stream, then we have to skip threads that
???? * didn't output a frame, because we don't want to accidentally signal
???? * EOF (avpkt->size == 0 && *got_picture_ptr == 0).//因為我們不希望發生意外信號EOF，所以在流的最后，我們必須跳過線程，而不輸出幀
???? */
??? do {
??????? p = &fctx->threads[finished++];
??????? if (p->state != STATE_INPUT_READY) {
??????????? pthread_mutex_lock(&p->progress_mutex);
??????????? while (p->state != STATE_INPUT_READY) //如果數據的狀態不是STATE_INPUT_READY，線程進行等待，直到線程pthread_cond_signal(&p->progress_cond);
??????????????? pthread_cond_wait(&p->output_cond, &p->progress_mutex);
??????????? pthread_mutex_unlock(&p->progress_mutex);
??????? }
??????? av_frame_move_ref(picture, &p->frame);
??????? *got_picture_ptr = p->got_frame;
??????? picture->pkt_dts = p->avpkt.dts;
??????? /*
???????? * A later call with avkpt->size == 0 may loop over all threads,
???????? * including this one, searching for a frame to return before being
???????? * stopped by the "finished != fctx->next_finished" condition.
???????? * Make sure we don't mistakenly return the same frame again.
???????? */
??????? p->got_frame = 0;
??????? if (finished >= avctx->thread_count) finished = 0;
??? } while (!avpkt->size && !*got_picture_ptr && finished != fctx->next_finished);
??? update_context_from_thread(avctx, p->avctx, 1);
??? if (fctx->next_decoding >= avctx->thread_count) fctx->next_decoding = 0;
??? fctx->next_finished = finished;
??? /* return the size of the consumed packet if no error occurred */
??? return (p->result >= 0) ? avpkt->size : p->result;
}
注釋：
1.
/**
???? * thread opaque
???? * Can be used by execute() to store some per AVCodecContext stuff.
//能夠使用execute()函數來存儲每個AVCodecContext數據
???? * - encoding: set by execute()
???? * - decoding: set by execute()
???? */
??? void *thread_opaque;
2.
/**
?* Context used by codec threads and stored in their AVCodecContext thread_opaque.
?*/
typedef struct PerThreadContext {
??? struct FrameThreadContext *parent;
??? pthread_t????? thread;
??? int??????????? thread_init;
??? pthread_cond_t input_cond;????? ///< Used to wait for a new packet from the main thread.從主線程等待一個新的數據包。
??? pthread_cond_t progress_cond;?? ///< Used by child threads to wait for progress to change.
??? pthread_cond_t output_cond;???? ///< Used by the main thread to wait for frames to finish.用于由主線程等待幀來完成
??? pthread_mutex_t mutex;????????? ///< Mutex used to protect the contents of the PerThreadContext.
??? pthread_mutex_t progress_mutex; ///< Mutex used to protect frame progress values and progress_cond.
??? AVCodecContext *avctx;????????? ///< Context used to decode packets passed to this thread.
??? AVPacket?????? avpkt;?????????? ///< Input packet (for decoding) or output (for encoding).
??? uint8_t?????? *buf;???????????? ///< backup storage for packet data when the input packet is not refcounted
??? int??????????? allocated_buf_size; ///< Size allocated for buf
??? AVFrame frame;????????????????? ///< Output frame (for decoding) or input (for encoding).
??? int???? got_frame;????????????? ///< The output of got_picture_ptr from the last avcodec_decode_video() call.
??? int???? result;???????????????? ///< The result of the last codec decode/encode() call.
??? enum {?? //這個可以看之前文章中提到的幀級解碼狀態圖
??????? STATE_INPUT_READY,????????? ///< Set when the thread is awaiting a packet.
??????? STATE_SETTING_UP,?????????? ///< Set before the codec has called ff_thread_finish_setup().
??????? STATE_GET_BUFFER,?????????? /**<
???????????????????????????????????? * Set when the codec calls get_buffer().
???????????????????????????????????? * State is returned to STATE_SETTING_UP afterwards.
???????????????????????????????????? */
??????? STATE_SETUP_FINISHED??????? ///< Set after the codec has called ff_thread_finish_setup().
??? } state;
??? /**
???? * Array of frames passed to ff_thread_release_buffer().
???? * Frames are released after all threads referencing them are finished.
???? */
??? AVFrame *released_buffers;
??? int? num_released_buffers;
??? int????? released_buffers_allocated;
??? AVFrame *requested_frame;?????? ///< AVFrame the codec passed to get_buffer()
??? int????? requested_flags;?????? ///< flags passed to get_buffer() for requested_frame
} PerThreadContext;
FFmepg 多線程解碼歷程 - 4:avcodec_open2
//在初始化codec后，接下來就是打開解碼器int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options)
{
??? int ret = 0;
??? AVDictionary *tmp = NULL;
??? if (avcodec_is_open(avctx))? //返回avctx-》internal，見注釋1
??????? return 0;
??? 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;
//判斷額外數據，在硬解嗎h264的時候必須人為設置sps pps給extradata
??? if (avctx->extradata_size < 0 || avctx->extradata_size >= FF_MAX_EXTRADATA_SIZE)
??????? return AVERROR(EINVAL);
??? if (options)?? //一般options設置NULL
??????? av_dict_copy(&tmp, *options, 0);
??? ret = ff_lock_avcodec(avctx);
??? if (ret < 0)
??????? return ret;
??? avctx->internal = av_mallocz(sizeof(AVCodecInternal));
??? if (!avctx->internal) {
??????? ret = AVERROR(ENOMEM);
??????? goto end;
??? }
??? avctx->internal->pool = av_mallocz(sizeof(*avctx->internal->pool));
??? if (!avctx->internal->pool) {
??????? ret = AVERROR(ENOMEM);
??????? goto free_and_end;
??? }
??? 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 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;
??? } //上面主要是分配內存
??? if ((ret = av_opt_set_dict(avctx, &tmp)) < 0)
??????? goto free_and_end;
??? // only call avcodec_set_dimensions() for non H.264/VP6F codecs so as not to overwrite previously setup dimensions
??? 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))) {
??? if (avctx->coded_width && avctx->coded_height)
??????? avcodec_set_dimensions(avctx, avctx->coded_width, avctx->coded_height);
??? else if (avctx->width && avctx->height)
??????? avcodec_set_dimensions(avctx, avctx->width, avctx->height);
??? }
??? if ((avctx->coded_width || avctx->coded_height || avctx->width || avctx->height)
??????? && (? av_image_check_size(avctx->coded_width, avctx->coded_height, 0, avctx) < 0
?????????? || av_image_check_size(avctx->width,?????? avctx->height,?????? 0, avctx) < 0)) {
??????? av_log(avctx, AV_LOG_WARNING, "Ignoring invalid width/height values\n");
??????? avcodec_set_dimensions(avctx, 0, 0);
??? }
?? ? /* if the decoder init function was already called previously,如果解碼器的init函數已經調用過
???? * free the already allocated subtitle_header before overwriting it 釋放已經分配subtitle_header ，在它覆蓋前
*/
??? if (av_codec_is_decoder(codec))
??????? av_freep(&avctx->subtitle_header);
??? if (avctx->channels > FF_SANE_NB_CHANNELS) {
??????? 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);
??? if (avctx->codec->capabilities & CODEC_CAP_EXPERIMENTAL &&
??????? avctx->strict_std_compliance > FF_COMPLIANCE_EXPERIMENTAL) {
??????? const char *codec_string = av_codec_is_encoder(codec) ? "encoder" : "decoder";
??????? AVCodec *codec2;
??????? av_log(NULL, 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 & CODEC_CAP_EXPERIMENTAL))
??????????? av_log(NULL, 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;
??? }
??? if (!HAVE_THREADS)
??????? av_log(avctx, AV_LOG_WARNING, "Warning: not compiled with thread support, using thread emulation\n");
??? if (CONFIG_FRAME_THREAD_ENCODER) {
??????? ff_unlock_avcodec(); //we will instanciate a few encoders thus kick the counter to prevent false detection of a problem
??????? ret = ff_frame_thread_encoder_init(avctx, options ? *options : NULL);
??????? ff_lock_avcodec(avctx);
??????? if (ret < 0)
??????????? goto free_and_end;
??? }
//幀線程編碼
??? if (HAVE_THREADS && !avctx->thread_opaque
??????? && !(avctx->internal->frame_thread_encoder && (avctx->active_thread_type&FF_THREAD_FRAME))) {
??????? ret = ff_thread_init(avctx);//會根據用戶設置不同的變量來判斷是片，幀，來初始化線程
??????? if (ret < 0) {
??????????? goto free_and_end;
??????? }
??? }
??? if (!HAVE_THREADS && !(codec->capabilities & CODEC_CAP_AUTO_THREADS))
??????? avctx->thread_count = 1;
??? if (avctx->codec->max_lowres < avctx->lowres || avctx->lowres < 0) {
??????? av_log(avctx, AV_LOG_ERROR, "The maximum value for lowres supported by the decoder is %d\n",
?????????????? avctx->codec->max_lowres);
??????? ret = AVERROR(EINVAL);
??????? goto free_and_end;
??? }
//下面就會根據是編碼器還是解碼器來初始化
??? if (av_codec_is_encoder(avctx->codec)) {
??????? int i;
??????? if (avctx->codec->sample_fmts) {
??????????? for (i = 0; avctx->codec->sample_fmts[i] != AV_SAMPLE_FMT_NONE; i++) {
??????????????? if (avctx->sample_fmt == avctx->codec->sample_fmts[i])
??????????????????? break;
??????????????? if (avctx->channels == 1 &&
??????????????????? av_get_planar_sample_fmt(avctx->sample_fmt) ==
??????????????????? av_get_planar_sample_fmt(avctx->codec->sample_fmts[i])) {
??????????????????? avctx->sample_fmt = avctx->codec->sample_fmts[i];
??????????????????? break;
??????????????? }
??????????? }
??????????? if (avctx->codec->sample_fmts[i] == AV_SAMPLE_FMT_NONE) {
??????????????? char buf[128];
??????????????? snprintf(buf, sizeof(buf), "%d", avctx->sample_fmt);
??????????????? av_log(avctx, AV_LOG_ERROR, "Specified sample format %s is invalid or not supported\n",
?????????????????????? (char *)av_x_if_null(av_get_sample_fmt_name(avctx->sample_fmt), buf));
??????????????? ret = AVERROR(EINVAL);
??????????????? goto free_and_end;
??????????? }
??????? }
??????? if (avctx->codec->pix_fmts) {
??????????? for (i = 0; avctx->codec->pix_fmts[i] != AV_PIX_FMT_NONE; i++)
??????????????? if (avctx->pix_fmt == avctx->codec->pix_fmts[i])
??????????????????? break;
??????????? if (avctx->codec->pix_fmts[i] == AV_PIX_FMT_NONE
??????????????? && !((avctx->codec_id == AV_CODEC_ID_MJPEG || avctx->codec_id == AV_CODEC_ID_LJPEG)
???????????????????? && avctx->strict_std_compliance <= FF_COMPLIANCE_UNOFFICIAL)) {
??????????????? char buf[128];
??????????????? snprintf(buf, sizeof(buf), "%d", avctx->pix_fmt);
??????????????? av_log(avctx, AV_LOG_ERROR, "Specified pixel format %s is invalid or not supported\n",
?????????????????????? (char *)av_x_if_null(av_get_pix_fmt_name(avctx->pix_fmt), buf));
??????????????? ret = AVERROR(EINVAL);
??????????????? goto free_and_end;
??????????? }
??????? }
??????? if (avctx->codec->supported_samplerates) {
??????????? for (i = 0; avctx->codec->supported_samplerates[i] != 0; i++)
??????????????? if (avctx->sample_rate == avctx->codec->supported_samplerates[i])
??????????????????? break;
??????????? if (avctx->codec->supported_samplerates[i] == 0) {
??????????????? av_log(avctx, AV_LOG_ERROR, "Specified sample rate %d is not supported\n",
?????????????????????? avctx->sample_rate);
??????????????? ret = AVERROR(EINVAL);
??????????????? goto free_and_end;
??????????? }
??????? }
??????? if (avctx->codec->channel_layouts) {
??????????? if (!avctx->channel_layout) {
??????????????? av_log(avctx, AV_LOG_WARNING, "Channel layout not specified\n");
??????????? } else {
??????????????? for (i = 0; avctx->codec->channel_layouts[i] != 0; i++)
??????????????????? if (avctx->channel_layout == avctx->codec->channel_layouts[i])
??????????????????????? break;
??????????????? if (avctx->codec->channel_layouts[i] == 0) {
??????????????????? char buf[512];
??????????????????? av_get_channel_layout_string(buf, sizeof(buf), -1, avctx->channel_layout);
??????????????????? av_log(avctx, AV_LOG_ERROR, "Specified channel layout '%s' is not supported\n", buf);
??????????????????? ret = AVERROR(EINVAL);
??????????????????? goto free_and_end;
??????????????? }
??????????? }
??????? }
??????? if (avctx->channel_layout && avctx->channels) {
??????????? int channels = av_get_channel_layout_nb_channels(avctx->channel_layout);
??????????? if (channels != avctx->channels) {
??????????????? char buf[512];
??????????????? av_get_channel_layout_string(buf, sizeof(buf), -1, avctx->channel_layout);
??????????????? av_log(avctx, AV_LOG_ERROR,
?????????????????????? "Channel layout '%s' with %d channels does not match number of specified channels %d\n",
?????????????????????? buf, channels, avctx->channels);
??????????????? ret = AVERROR(EINVAL);
??????????????? goto free_and_end;
??????????? }
??????? } else if (avctx->channel_layout) {
??????????? avctx->channels = av_get_channel_layout_nb_channels(avctx->channel_layout);
??????? }
??????? if(avctx->codec_type == AVMEDIA_TYPE_VIDEO &&
?????????? avctx->codec_id != AV_CODEC_ID_PNG // For mplayer
??????? ) {
??????????? if (avctx->width <= 0 || avctx->height <= 0) {
??????????????? av_log(avctx, AV_LOG_ERROR, "dimensions not set\n");
??????????????? ret = AVERROR(EINVAL);
??????????????? goto free_and_end;
??????????? }
??????? }
??????? if (?? (avctx->codec_type == AVMEDIA_TYPE_VIDEO || avctx->codec_type == AVMEDIA_TYPE_AUDIO)
??????????? && avctx->bit_rate>0 && avctx->bit_rate<1000) {
??????????? av_log(avctx, AV_LOG_WARNING, "Bitrate %d is extremely low, maybe you mean %dk\n", avctx->bit_rate, avctx->bit_rate);
??????? }
??????? if (!avctx->rc_initial_buffer_occupancy)
??????????? avctx->rc_initial_buffer_occupancy = avctx->rc_buffer_size * 3 / 4;
??? }
??? avctx->pts_correction_num_faulty_pts =
??? avctx->pts_correction_num_faulty_dts = 0;
??? avctx->pts_correction_last_pts =
??? avctx->pts_correction_last_dts = INT64_MIN;
??? if (?? avctx->codec->init && (!(avctx->active_thread_type&FF_THREAD_FRAME)
??????? || avctx->internal->frame_thread_encoder)) {
??????? ret = avctx->codec->init(avctx);
??????? if (ret < 0) {
??????????? goto free_and_end;
??????? }
??? }
??? ret=0;
//上面部分是判斷codec是否是編碼器，然后如果是編碼器則進行選擇編碼的方式，這里我們只討論解碼，下面的解碼器也是一樣，根據不同的條件，進行編碼初始化
??? if (av_codec_is_decoder(avctx->codec)) {
??????? if (!avctx->bit_rate)
??????????? avctx->bit_rate = get_bit_rate(avctx);//如果沒有設置bit_rate則會更加avctx類型將avctx->bit_rate復制給
??????? /* 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->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) {
??????????????????????? av_log(avctx, AV_LOG_ERROR, "Unable to open iconv context "
?????????????????????????????? "with input character encoding \"%s\"\n", avctx->sub_charenc);
??????????????????????? ret = AVERROR(errno);
??????????????????????? 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
??????????????? }
??????????? }
??????? }
??? }
end:
??? ff_unlock_avcodec();
??? if (options) {
??????? av_dict_free(options);
??????? *options = tmp;
??? }
??? return ret;
free_and_end:
??? av_dict_free(&tmp);
??? av_freep(&avctx->priv_data);
??? if (avctx->internal)
??????? av_freep(&avctx->internal->pool);
??? av_freep(&avctx->internal);
??? avctx->codec = NULL;
??? goto end;
}
注釋：
1.?/**
???? * Private context used for internal data.
???? *私有的上下文內容用于內部數據
???? * Unlike priv_data, this is not codec-specific. It is used in general
???? * libavcodec functions.
*不像priv_data ，這是不特定的編解碼器。這是用在一般libavcodec的功能
???? */
??? struct AVCodecInternal *internal;
FFmepg 多線程解碼歷程 - 5： ff_thread_init
//用來判斷是幀還是片線程初始化int ff_thread_init(AVCodecContext *avctx)
{
??? if (avctx->thread_opaque) {
??????? av_log(avctx, AV_LOG_ERROR, "avcodec_thread_init is ignored after avcodec_open\n");
??????? return -1;
??? }
#if HAVE_W32THREADS
??? w32thread_init();
#endif
??? if (avctx->codec) {
?? ??? ? //有效的線程參數，將會設置avctx->active_thread_type，進而判斷進入下面if的哪個條件
??????? validate_thread_parameters(avctx);// 查看FFmepg 多線程解碼歷程 - 1:validate_thread_parameters 講解
?? ??? ?
??????? if (avctx->active_thread_type&FF_THREAD_SLICE)
??????????? return thread_init(avctx);
??????? else if (avctx->active_thread_type&FF_THREAD_FRAME)
??????????? return frame_thread_init(avctx);? //下一篇講解frame_thread_init的具體內容
??? }
??? return 0;
}
FFmepg 多線程解碼歷程 - 6：frame_thread_init
//ff_thread_init選擇幀線程初始化，就會進入frame_thread_init
static int frame_thread_init(AVCodecContext *avctx)
{??? int thread_count = avctx->thread_count;
??? const AVCodec *codec = avctx->codec;
??? AVCodecContext *src = avctx;
??? FrameThreadContext *fctx;
??? int i, err = 0;
//如果我們在初始化codec的時候沒有設置thread_count或者設置為0，則就會自動根據手機設備來獲取
??? if (!thread_count) {
??????? int nb_cpus = ff_get_logical_cpus(avctx);
??????? if ((avctx->debug & (FF_DEBUG_VIS_QP | FF_DEBUG_VIS_MB_TYPE)) || avctx->debug_mv)
??????????? nb_cpus = 1;
??????? // 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);? //#define FFMIN(a,b) ((a) > (b) ? (b) : (a))
??????? else
??????????? thread_count = avctx->thread_count = 1;
??? }
??? if (thread_count <= 1) {? //如果thread_count <= 1那么即使進入幀級線程初始化，在解碼的時候也不會調用幀級解碼函數的
??????? avctx->active_thread_type = 0;
??????? return 0;
??? }
??? avctx->thread_opaque = fctx = av_mallocz(sizeof(FrameThreadContext));
??? fctx->threads = av_mallocz(sizeof(PerThreadContext) * thread_count);? //相當與初始化線程池，個數就是thread_count
??? pthread_mutex_init(&fctx->buffer_mutex, NULL);
??? fctx->delaying = 1;
??? for (i = 0; i < thread_count; i++) {
??????? AVCodecContext *copy = av_malloc(sizeof(AVCodecContext));
??????? PerThreadContext *p? = &fctx->threads[i];
??????? pthread_mutex_init(&p->mutex, NULL);
??????? pthread_mutex_init(&p->progress_mutex, NULL);
??????? pthread_cond_init(&p->input_cond, NULL);
??????? pthread_cond_init(&p->progress_cond, NULL);
??????? pthread_cond_init(&p->output_cond, NULL);
??????? p->parent = fctx;
??????? p->avctx? = copy;
??????? if (!copy) {
??????????? err = AVERROR(ENOMEM);
??????????? goto error;
??????? }
??????? *copy = *src;
??????? copy->thread_opaque = p;
??????? copy->pkt = &p->avpkt;
??????? if (!i) {
??????????? src = copy;
??????????? if (codec->init)
??????????????? err = codec->init(copy);
?? ??? ?//更新下一個線程的AVCodecContext參考線程的上下文中的值
??????????? update_context_from_thread(avctx, copy, 1);
??????? } else {
??????????? copy->priv_data = av_malloc(codec->priv_data_size);
??????????? if (!copy->priv_data) {
??????????????? err = AVERROR(ENOMEM);
??????????????? goto error;
??????????? }
??????????? memcpy(copy->priv_data, src->priv_data, codec->priv_data_size);
??????????? copy->internal = av_malloc(sizeof(AVCodecInternal));
??????????? if (!copy->internal) {
??????????????? err = AVERROR(ENOMEM);
??????????????? goto error;
??????????? }
??????????? *copy->internal = *src->internal;
??????????? copy->internal->is_copy = 1;
??????????? if (codec->init_thread_copy)
??????????????? err = codec->init_thread_copy(copy);
??????? }
??????? if (err) goto error;
/ //下面出創建線程，調用frame_worker_thread
??????? err = AVERROR(pthread_create(&p->thread, NULL, frame_worker_thread, p));
??????? p->thread_init= !err;
??????? if(!p->thread_init)
??????????? goto error;
??? }
??? return 0;
error:
??? frame_thread_free(avctx, i+1);
??? return err;
}
FFmepg 多線程解碼歷程 - 7：submit_packet
//在ff_thread_decode_frame中會調用submit_packet將碼流交給對應的解碼線程，來實現線程狀態的改變，具體的流程圖見下面圖
static int submit_packet(PerThreadContext *p, AVPacket *avpkt)
{??? FrameThreadContext *fctx = p->parent;
??? PerThreadContext *prev_thread = fctx->prev_thread;
??? const AVCodec *codec = p->avctx->codec;
??? if (!avpkt->size && !(codec->capabilities & CODEC_CAP_DELAY)) return 0;
??? pthread_mutex_lock(&p->mutex);
??? release_delayed_buffers(p);
??? if (prev_thread) {
??????? int err;
??????? if (prev_thread->state == STATE_SETTING_UP) {
??????????? pthread_mutex_lock(&prev_thread->progress_mutex);
??????????? while (prev_thread->state == STATE_SETTING_UP)? //判斷之前的線程狀態為STATE_SETTING_UP的時候，進行線程的等待，
??????????????? pthread_cond_wait(&prev_thread->progress_cond, &prev_thread->progress_mutex);
??????????? pthread_mutex_unlock(&prev_thread->progress_mutex);
??????? }
??????? err = update_context_from_thread(p->avctx, prev_thread->avctx, 0);//如果之前的線程狀態變為STATE_SETUP_FINISHED，然后從線程中哦功能更新內容
??????? if (err) {
??????????? pthread_mutex_unlock(&p->mutex);
??????????? return err;
??????? }
??? }
??? av_buffer_unref(&p->avpkt.buf);
??? p->avpkt = *avpkt;
??? if (avpkt->buf)
??????? p->avpkt.buf = av_buffer_ref(avpkt->buf);
??? else {
??????? av_fast_malloc(&p->buf, &p->allocated_buf_size, avpkt->size + FF_INPUT_BUFFER_PADDING_SIZE);
??????? p->avpkt.data = p->buf;
??????? memcpy(p->buf, avpkt->data, avpkt->size);
??????? memset(p->buf + avpkt->size, 0, FF_INPUT_BUFFER_PADDING_SIZE);
??? }
??? p->state = STATE_SETTING_UP;
??? pthread_cond_signal(&p->input_cond);//發送碼流輸入準備好的信號給解碼線程pthread_cond_waite(&p->input_cond),讓解碼線程
??? pthread_mutex_unlock(&p->mutex);
??? /*
???? * If the client doesn't have a thread-safe get_buffer(),
???? * then decoding threads call back to the main thread,
???? * and it calls back to the client here.
???? */
??? if (!p->avctx->thread_safe_callbacks && (
#if FF_API_GET_BUFFER
???????? p->avctx->get_buffer ||
#endif
???????? p->avctx->get_buffer2 != avcodec_default_get_buffer2)) {
??????? while (p->state != STATE_SETUP_FINISHED && p->state != STATE_INPUT_READY) {
??????????? pthread_mutex_lock(&p->progress_mutex);
??????????? while (p->state == STATE_SETTING_UP)
??????????????? pthread_cond_wait(&p->progress_cond, &p->progress_mutex);
??????????? if (p->state == STATE_GET_BUFFER) {
??????????????? p->result = ff_get_buffer(p->avctx, p->requested_frame, p->requested_flags);
??????????????? p->state? = STATE_SETTING_UP;
??????????????? pthread_cond_signal(&p->progress_cond);
??????????? }
??????????? pthread_mutex_unlock(&p->progress_mutex);
??????? }
??? }
??? fctx->prev_thread = p;
??? fctx->next_decoding++;
??? return 0;
}
主線程接收數據，準備完畢后發出pthread_cond_signal(&p->input_cond)信號，然后解碼線程接收到以后，設置線程狀態為finish_setup，發送廣播p->process_cond，進行解碼，
解碼線程解完以后，發送p->progress_cond信號，主線程回調，從解碼線程中獲取get_buffer，解碼之后的數據，然后發送p->progress_cond信號給解碼線程，然后解碼線程發出p->output_cond信號給主線程，主線程輸出解碼之后的frame給用戶
注釋1：
總結
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