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• Add padding with ffmpeg to videos increases file size, why ?

  12 mars 2023, par try2getsmarter

  I need to add padding to mp4 video files (since tv changes aspect ratio on playback) and I simply can do this with -pad option of ffmpeg.

  


  The output is ok for me, but I see that most of the video files increase about 25%-30% in file size.

  


  ffmpeg -i in.mp4 -preset slow -vf "pad=1920:1080 :(1920-iwmin(1920/iw,1080/ih))/2 :(1080-ihmin(1920/iw,1080/ih))/2" -c:v h264 -c:a copy out_fhd.mp4"

  


  Is there a way to preserve the input quality and have the same file size ? As the black bars contain no information I had the expectation that there is a lossless mode to take the already H264 encoded stream and just add blocks with black pixels.

  


• libvlc ffmpeg : No seek in mpegts h264 stream

  26 juillet 2016, par ElDorado

  I am using ffmpeg to record video input from GDI (windows screen recorder) to view it later using VLC (via ActiveX plugin) + ffmpeg to decode it.

  Right now seeking in video is not working in VLC via plugin (which is critical). VLC player itself provide seeking, but it is more like byte position seeking (on I- frames which are larger than other frames it makes larger steps on horizontal scroll and also there are no timestamps).

  Encoder is opened with next defaults :

  avformat_alloc_output_context2(&outputContext, NULL, "mpegts", "test.mpg");
  
  outputFormat = outputContext->oformat;
  
  encoder = avcodec_find_encoder(AV_CODEC_ID_H264);
  
  outputStream = avformat_new_stream(outputContext, encoder);
  
  outputStream->id = outputContext->nb_streams - 1;
  
  encoderContext = outputStream->codec;
  
  encoderContext->bit_rate = bitrate;   // 800000 by default
  
  encoderContext->rc_max_rate = bitrate;
  
  encoderContext->width = imageWidth;   // 1920
  
  encoderContext->height = imageHeight; // 1080
  
  encoderContext->time_base.num = 1;
  
  encoderContext->time_base.den = fps;  // 25 by default
  
  encoderContext->gop_size = fps;
  
  encoderContext->keyint_min = fps;
  
  encoderContext->max_b_frames = 0;
  
  encoderContext->pix_fmt = AV_PIX_FMT_YUV420P;
  
  outputStream->time_base = encoderContext->time_base;
  
  avcodec_open2(encoderContext, encoder, NULL);

  Recording is done this way :

  // my impl of GDI recorder, returning AVFrame with only data and linesize filled.
  
  AVFrame* tmp_frame = impl_->recorder->acquireFrame();
  
  
  
  // converting RGB -> YUV420
  
  sws_scale(impl_->scaleContext, tmp_frame->data, tmp_frame->linesize, 0, impl_->frame->height, impl_->frame->data, impl_->frame->linesize);
  
  
  
  // pts variable is calculated by using QueryPerformanceCounter form WinAPI. It is strictly increasing
  
  impl_->frame->pts = pts;
  
  
  
  avcodec_encode_video2(impl_->encoderContext, impl_->packet, impl_->frame, &out_size);
  
  
  
  if (out_size) {
  
       impl_->packet->pts = pts;
  
       impl_->packet->dts = pts;
  
       impl_->packet->duration = 1; // here it is! It is set but has no effect
  
       av_packet_rescale_ts(impl_->packet, impl_->encoderContext->time_base, impl_->outputStream->time_base);
  
       // here pts = 3600*pts, dts = 3600*pts, duration = 3600 what I consider to be legit in terms of milliseconds
  
       impl_->packet->stream_index = impl_->outputStream->index;
  
       av_interleaved_write_frame(impl_->outputContext, impl_->packet);
  
       av_packet_unref(impl_->packet);
  
       out_size = 0;
  
  }

  ffprobe is providing next info on frames :

  [FRAME]
  
  media_type=video
  
  stream_index=0
  
  key_frame=1
  
  pkt_pts=3600
  
  pkt_pts_time=0:00:00.040000
  
  pkt_dts=3600
  
  pkt_dts_time=0:00:00.040000
  
  best_effort_timestamp=3600
  
  best_effort_timestamp_time=0:00:00.040000
  
  pkt_duration=N/A
  
  pkt_duration_time=N/A
  
  pkt_pos=564
  
  pkt_size=97.018555 Kibyte
  
  width=1920
  
  height=1080
  
  pix_fmt=yuv420p
  
  sample_aspect_ratio=N/A
  
  pict_type=I
  
  coded_picture_number=0
  
  display_picture_number=0
  
  interlaced_frame=0
  
  top_field_first=0
  
  repeat_pict=0
  
  [/FRAME]

  I believe that problem is in pkt_duration variable, though it was set.
  What I am doing wrong in recording so I can’t seek in video ?

  P.S. on other videos (also h264) seeking is working in ActiveX VLC plugin.

• Revision 30966 : eviter le moche ’doctype_ecrire’ lors de l’upgrade

  17 août 2009, par fil@… — Log

  eviter le moche ’doctype_ecrire’ lors de l’upgrade