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• How to explain the given ffplay C code snippet ?

  20 juillet 2015, par Jerikc XIONG

  The following code snippet is from ffplay :

  static int decoder_decode_frame(Decoder *d, AVFrame *frame, AVSubtitle *sub) {
  
      int got_frame = 0;
  
  
  
      do {
  
          int ret = -1;
  
  
  
          if (d->queue->abort_request)
  
              return -1;
  
  
  
          if (!d->packet_pending || d->queue->serial != d->pkt_serial) {
  
              AVPacket pkt;
  
              do {
  
                  if (d->queue->nb_packets == 0)
  
                      SDL_CondSignal(d->empty_queue_cond);
  
                  if (packet_queue_get(d->queue, &pkt, 1, &d->pkt_serial) < 0)
  
                      return -1;
  
                  if (pkt.data == flush_pkt.data) {
  
                      avcodec_flush_buffers(d->avctx);
  
                      d->finished = 0;
  
                      d->next_pts = d->start_pts;
  
                      d->next_pts_tb = d->start_pts_tb;
  
                  }
  
              } while (pkt.data == flush_pkt.data || d->queue->serial != d->pkt_serial);
  
              av_free_packet(&d->pkt);
  
              d->pkt_temp = d->pkt = pkt;
  
              d->packet_pending = 1;
  
          }
  
  
  
          switch (d->avctx->codec_type) {
  
              case AVMEDIA_TYPE_VIDEO:
  
                  ret = avcodec_decode_video2(d->avctx, frame, &got_frame, &d->pkt_temp);
  
                  if (got_frame) {
  
                      if (decoder_reorder_pts == -1) {
  
                          frame->pts = av_frame_get_best_effort_timestamp(frame);
  
                      } else if (decoder_reorder_pts) {
  
                          frame->pts = frame->pkt_pts;
  
                      } else {
  
                          frame->pts = frame->pkt_dts;
  
                      }
  
                  }
  
                  break;
  
              case AVMEDIA_TYPE_AUDIO:
  
                  ret = avcodec_decode_audio4(d->avctx, frame, &got_frame, &d->pkt_temp);
  
                  if (got_frame) {
  
                      AVRational tb = (AVRational){1, frame->sample_rate};
  
                      if (frame->pts != AV_NOPTS_VALUE)
  
                          frame->pts = av_rescale_q(frame->pts, d->avctx->time_base, tb);
  
                      else if (frame->pkt_pts != AV_NOPTS_VALUE)
  
                          frame->pts = av_rescale_q(frame->pkt_pts, av_codec_get_pkt_timebase(d->avctx), tb);
  
                      else if (d->next_pts != AV_NOPTS_VALUE)
  
                          frame->pts = av_rescale_q(d->next_pts, d->next_pts_tb, tb);
  
                      if (frame->pts != AV_NOPTS_VALUE) {
  
                          d->next_pts = frame->pts + frame->nb_samples;
  
                          d->next_pts_tb = tb;
  
                      }
  
                  }
  
                  break;
  
              case AVMEDIA_TYPE_SUBTITLE:
  
                  ret = avcodec_decode_subtitle2(d->avctx, sub, &got_frame, &d->pkt_temp);
  
                  break;
  
          }
  
  
  
          if (ret < 0) {
  
              d->packet_pending = 0;
  
          } else {
  
              d->pkt_temp.dts =
  
              d->pkt_temp.pts = AV_NOPTS_VALUE;
  
              if (d->pkt_temp.data) {
  
                  if (d->avctx->codec_type != AVMEDIA_TYPE_AUDIO)
  
                      ret = d->pkt_temp.size;
  
                  d->pkt_temp.data += ret;
  
                  d->pkt_temp.size -= ret;
  
                  if (d->pkt_temp.size <= 0)
  
                      d->packet_pending = 0;
  
              } else {
  
                  if (!got_frame) {
  
                      d->packet_pending = 0;
  
                      d->finished = d->pkt_serial; // FLAG
  
                  }
  
              }
  
          }
  
      } while (!got_frame && !d->finished);
  
  
  
      return got_frame;
  
  }

  It’s difficult for me to understand the following code :

  d->finished = d->pkt_serial; // FLAG

  Can anyone help me ?

  Thanks.

• C++, FFmpeg, save AVPacket infomation into videostate structure in ffplay.c

  28 mai 2015, par Yoohoo

  I am currently working on a project that tests video streaming. In the project, video stream is encoded with H.264 before send and decoded after receive, using FFmpeg codec and functions.

  I can encode video stream by

  init_video_encode(AV_CODEC_ID_H264);

  where

  static void init_video_encode(AVCodecID codec_id){
  
  codec = avcodec_find_encoder(codec_id);
  
  if (!codec) {
  
      fprintf(stderr, "Codec not found\n");
  
      exit(1);
  
  }
  
  
  
  c = avcodec_alloc_context3(codec);
  
  if (!c) {
  
      fprintf(stderr, "Could not allocate video codec context\n");
  
      exit(1);
  
  }
  
  
  
  /* put sample parameters */
  
  c->bit_rate = 400000;
  
  /* resolution must be a multiple of two */
  
  c->width = 640;
  
  c->height = 480;
  
  /* frames per second */
  
  c->time_base= (AVRational){1,25};
  
  c->gop_size = 10; /* emit one intra frame every ten frames */
  
  c->max_b_frames=max_f;
  
  c->pix_fmt = AV_PIX_FMT_YUV420P;
  
  
  
  if(codec_id == AV_CODEC_ID_H264)
  
      av_opt_set(c->priv_data, "preset", "slow", 0);
  
  
  
  /* open it */
  
  if (avcodec_open2(c, codec, NULL) < 0) {
  
      fprintf(stderr, "Could not open codec\n");
  
      exit(1);
  
  }
  
  
  
  frame = avcodec_alloc_frame();
  
  if (!frame) {
  
      fprintf(stderr, "Could not allocate video frame\n");
  
      exit(1);
  
  }
  
  frame->format = c->pix_fmt;
  
  frame->width  = c->width;
  
  frame->height = c->height;
  
  
  
  /* the image can be allocated by any means and av_image_alloc() is
  
   * just the most convenient way if av_malloc() is to be used */
  
  ret = av_image_alloc(frame->data, frame->linesize, c->width, c->height,
  
                       c->pix_fmt, 32);
  
  
  
  /* get the delayed frames */
  
  if (ret < 0) {
  
      fprintf(stderr, "Could not allocate raw picture buffer\n");
  
      exit(1);
  
  }
  
      av_init_packet(&pkt);
  
  
  
  //}
  
  
  
      pkt.data = NULL;    // packet data will be allocated by the encoder
  
      pkt.size = 0;
  
      //cout<<"\nBefore YUV\n";
  
      if(count == 0)
  
      read_yuv420(frame->data[0]);
  
      count ++;
  
     // cout<<"\nAfter YUV\n";
  
      if(count == SUBSITY) {
  
      count = 0;
  
      }
  
  
  
      frame->pts = i++;
  
  
  
      /* encode the image */
  
      ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
  
      if (ret < 0) {
  
           fprintf(stderr, "Error encoding frame\n");
  
           return -1;
  
      }
  
      //cout<<"\nRecord the Video\n";
  
      if (got_output) {
  
           //printf("Write frame %3d (size=%5d)\n", i, pkt.size);
  
           //cout<<"\nBefore Memcpy\n\n\n";
  
  
  
           memcpy(inbufout+totalSize,pkt.data,pkt.size);
  
           //cout<<"\nAfter Memcpy\n\n\n";
  
           totalSize+=pkt.size;

  The video encoder works very well, if I write the encoded packet into a .h264 file, it can be played. But at the decoder side, I cannot decode the received packet with :

      codec = avcodec_find_decoder(AV_CODEC_ID_H264);
  
      if (!codec) {
  
          fprintf(stderr, "Codec not found\n");
  
          exit(1);
  
      }
  
  
  
      c = avcodec_alloc_context3(codec);
  
      if (!c) {
  
          fprintf(stderr, "Could not allocate video codec context\n");
  
          exit(1);
  
      }
  
  
  
      if(codec->capabilities&CODEC_CAP_TRUNCATED)
  
          c->flags|= CODEC_FLAG_TRUNCATED; 
  
  
  
      /* open it */
  
      if (avcodec_open2(c, codec, NULL) < 0) {
  
          fprintf(stderr, "Could not open codec\n");
  
          exit(1);
  
      }
  
  
  
      frame = avcodec_alloc_frame();
  
      if (!frame) {
  
          fprintf(stderr, "Could not allocate video frame\n");
  
          exit(1);
  
      }
  
  len = avcodec_decode_video2(avctx, frame, &got_frame, pkt);
  
      if (len < 0) {
  
          fprintf(stderr, "Error while decoding frame %d\n", *frame_count);
  
          return len;
  
      }

  The reason of failure is lacking parser, I have tried to build a parser but failed......

  Therefore I am wondering using ffplay.c as a header file in my receiver program so that I can use it as the decoder and player.

  I have took a look at ffplay.c, it actually fetch file into a videostate structure and processing it. The fetching part is from line 3188 of ffplay.c :

  VideoState *is;
  
  
  
      is = av_mallocz(sizeof(VideoState));
  
      if (!is)
  
          return NULL;
  
      av_strlcpy(is->filename, filename, sizeof(is->filename));
  
      is->iformat = iformat;
  
      is->ytop    = 0;
  
      is->xleft   = 0;
  
  
  
      /* start video display */
  
      if (frame_queue_init(&is->pictq, &is->videoq, VIDEO_PICTURE_QUEUE_SIZE, 1) < 0)
  
          goto fail;
  
      if (frame_queue_init(&is->subpq, &is->subtitleq, SUBPICTURE_QUEUE_SIZE, 0) < 0)
  
          goto fail;
  
      if (frame_queue_init(&is->sampq, &is->audioq, SAMPLE_QUEUE_SIZE, 1) < 0)
  
          goto fail;
  
  
  
      packet_queue_init(&is->videoq);
  
      packet_queue_init(&is->audioq);
  
      packet_queue_init(&is->subtitleq);
  
  
  
      is->continue_read_thread = SDL_CreateCond();
  
  
  
      init_clock(&is->vidclk, &is->videoq.serial);
  
      init_clock(&is->audclk, &is->audioq.serial);
  
      init_clock(&is->extclk, &is->extclk.serial);
  
      is->audio_clock_serial = -1;
  
      is->av_sync_type = av_sync_type;
  
      is->read_tid     = SDL_CreateThread(read_thread, is);
  
      if (!is->read_tid) {
  
  fail:
  
          stream_close(is);
  
          return NULL;
  
      }

  Now instead of fetching file, I want to modify ffplay.c code so that let it fetch the received packet, I can save received packet to AVPacket by

  static AVPacket avpkt;
  
  avpkt.data = inbuf;

  My question is : how to put AVPacket information into videostate structure ?

• ffmpeg C API - creating queue of frames

  25 mai 2016, par lupod

  I have created using the C API of ffmpeg a C++ application that reads frames from a file and writes them to a new file. Everything works fine, as long as I write immediately the frames to the output. In other words, the following structure of the program outputs the correct result (I put only the pseudocode for now, if needed I can also post some real snippets but the classes that I have created for handling the ffmpeg functionalities are quite large) :

  AVFrame* frame = av_frame_alloc();
  
  int got_frame;
  
  
  
  // readFrame returns 0 if file is ended, got frame = 1 if
  
  // a complete frame has been extracted
  
  while(readFrame(inputfile,frame, &got_frame)) {
  
    if (got_frame) {
  
      // I actually do some processing here
  
      writeFrame(outputfile,frame);
  
    }
  
  }
  
  av_frame_free(&frame);

  The next step has been to parallelize the application and, as a consequence, frames are not written immediately after they are read (I do not want to go into the details of the parallelization). In this case problems arise : there is some flickering in the output, as if some frames get repeated randomly. However, the number of frames and the duration of the output video remains correct.

  What I am trying to do now is to separate completely the reading from writing in the serial implementation in order to understand what is going on. I am creating a queue of pointers to frames :

  std::queue queue;
  
  int ret = 1, got_frame;
  
  while (ret) {
  
    AVFrame* frame = av_frame_alloc();
  
    ret = readFrame(inputfile,frame,&got_frame);
  
    if (got_frame) 
  
      queue.push(frame);
  
  }

  To write frames to the output file I do :

  while (!queue.empty()) {
  
    frame = queue.front();
  
    queue.pop();
  
    writeFrame(outputFile,frame);
  
    av_frame_free(&frame);
  
  }

  The result in this case is an output video with the correct duration and number of frames that is only a repetition of the last 3 (I think) frames of the video.

  My guess is that something might go wrong because of the fact that in the first case I use always the same memory location for reading frames, while in the second case I allocate many different frames.

  Any suggestions on what could be the problem ?