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• Set H264 high quality encoding in FFMPEG

  25 décembre 2015, par hiitiger

  I’m working on a function, using ffmpeg to encode a serial images to a MP4 file.
  I use H264 codec, and want to have a high quality output.

  Other things now goes well, but the video quality looks obvious loss.

  After some Google, I set codec context like this

  video_st = avformat_new_stream(oc, 0); 
  
  ....
  
  pVideoCodec  = avcodec_find_encoder(fmt->video_codec); //AV_CODEC_ID_H264
  
  ....
  
  avcodec_get_context_defaults3(video_st->codec, pVideoCodec);
  
  video_st->codec->codec_id =  fmt->video_codec;
  
  video_st->codec->width = m_outWidth;
  
  video_st->codec->height = m_outHeight;
  
  video_st->codec->time_base.den = m_fps;
  
  video_st->codec->time_base.num = 1;
  
  video_st->codec->pix_fmt = AV_PIX_FMT_YUV420P;
  
  
  
  AVDictionary *param = nullptr;
  
  av_dict_set(&param, "qp", "0", 0);
  
  av_dict_set(&param, "preset", "medium", 0);

  I also try to set bit_rate. But all turned out to be bad.

  I want a visually loss less output video.

  So what parameters should I set or anything else did I missed ?

• How to understand 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.

• Specify timestamp in ffmpeg video segment command

  25 mars 2019, par Soumya

  I have a continuous RTSP stream coming from a camera over the network.
  I want to dump the stream but in video files of length 1 min each.

  I an using the following command

  ffmpeg -i "rtsp://user:pass@example.com"  -f mp4 -r 12 -s 640x480 -ar 44100 \
  
  -ac 1 -segment_time 60 -segment_format mp4 "out%03d.mp4"

  The name of the files being created are of the form out001.mp4, out002.mp4, etc.

  I want to include the timestamp (hour and minute) in the name of the file segments eg. 09-30.mp4, 09-31.mp4, etc.

  If it is mandatory to provide a serial number for the segment, is it possible to get something like 09-30-001.mp4, 09-31-002.mp4 ?