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• Keeping the video stream alive when audio stream is missing

  26 avril 2020, par Core7s

  I have a current nginx setup where I am overlaying an audio stream on a video stream. The volume on the original video stream is dialed down so that the overlaid audio can be heard. This is achieved using ffmpeg as follows :
exec_push ffmpeg -i rtmp://localhost/original-video/{key} -i rtmp://localhost/overlaid-audio/{key} -filter_complex "[0:0]volume=0.03[lv]; [1:0]volume=0.97[hl]; [lv][hl] amix=inputs=2 [a]" -map 0:1 -map "[a]" -c:v copy -c:a aac -f flv rtmp://localhost/video-audio/mixed;

  



  My problem is, if the audio stream is not running the output doesn't work either. I want this setup to work whether the audio stream is active or not inactive. If the audio is inactive the original-video should get pushed to output without any change.

  



  Is there any filter or a conditional that can be used in the above setup to achieve that behavior ?

  


• Why do I lose PTS information when encoding to H264 ?

  1er mars 2019, par Nick

  I have a video file, with this video stream :

  ffmpeg -i original.avi

  Stream #0:0 : Video : h264 (Main) (H264 / 0x34363248), yuv420p(tv,
  bt709, progressive), 1920x1080 [SAR 1:1 DAR 16:9], 4204 kb/s, 59.94
  fps, 59.94 tbr, 59.94 tbn, 59.94 tbc

  I can get the PTS information by running :

  ffprobe -v 0 -of csv=p=0 -select_streams v -show_entries packet=pts_time original.avi

  And I get the PTS for each frame line by line :

  0.016683
  
  0.116783
  
  0.033367
  
  0.050050
  
  0.166833
  
  0.083417
  
  0.100100
  
  0.216883
  
  ...

  Now I need to encode the video to H264 and be able to get the same PTS information afterwards, so I used :

  ffmpeg -i original.avi -vcodec libx264 output.avi

  With this video stream :

  Stream #0:0 : Video : h264 (High) (H264 / 0x34363248),
  yuv420p(progressive), 1920x1080 [SAR 1:1 DAR 16:9], 2289 kb/s, 59.94
  fps, 59.94 tbr, 59.94 tbn, 119.88 tbc

  But when I try to get the PTS information from the output.avi I only get :

  N/A
  
  N/A
  
  N/A
  
  N/A
  
  N/A
  
  N/A
  
  ...

  What should I change in my command in order to keep the PTS information ?

• x264 Downsides of a high CRF (22) intermediary codec between conversions instead of lossless

  18 décembre 2019, par bobtheencoder

  I have a huge collection of video files that are in the range of CRF 16-20 taking up TB’s of space. The only need I have for these originals is that I have to encode them from time to time but the CRF of these final encodes is very low (CRF 26-28).

  I understand that a lossy to lossy converstion ALWAYS results in some quality loss but my question is what if the intermediate file is almost visually lossless compared to the final output.

  So to sum up, what quality difference should I expect from the following routes ?

  CRF 18 (original) -----> CRF 28 (final)
  
  CRF 18 (original) -----> CRF 22 (long-term storage) -----> Lossy  CRF 28 (final)