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• ffmpeg padding while leaving audio track unchanged

  17 janvier 2016, par mmj

  My cheap 16:9 TV is not able to play correctly a 1280x544 video (I see the 2.35:1 aspect ratio image vertically stretched to 16:9 aspect ratio, incomprehensibly the TV aspect ratio adjustment is disabled if source is USB), so I used ffmpeg (on Windows 10) to add two 88 pixels high horizontal black bars in order to get to a 1280x720 video with a 16:9 aspect ratio, using the following command :

  ffmpeg -i my_input_video.mkv -filter:v "pad=1280:720:0:88" my_output_video.mkv

  My TV play the new video correctly, but it says that the audio is not supported, whereas in the original video it was.

  How can I pad the original video leaving the audio track unchanged ?

• How can I concatenate MP4 videos and exactly match this combined video to an audio track in ffmpeg ?

  17 juin 2020, par mattador

  Basically I want to combine 4 videos into a single video, then swap out the concatenated audio for another track. The audio track needs to be unaltered and sync exactly to the video.

  



  Specifically, I'm creating multipaged dynamic audio spectrograms (visualizations of a sound file) using ggplot2 and gganimate in R, which I want to combine using ffmpeg. So the original WAV is chopped up into 3 sec segments, a video is created to visualize frequency changes over time for each segment, which I want to combine into 1 video with the original audio track matched up.

  



  All of my relevant files are at github here in the vids folder : DL link here

  



  The individual dynamic spectrograms export fine (1-4.mp4 in the archive). They are each 20ms too long ; they should be exactly 3s, but otherwise great.

  



  I then use ffmpeg to concatenate them :

  



  ffmpeg -f concat -safe 0 -i "mp4Segments.txt" -codec copy -t 12 -y "(1-4)vid.mp4"


  



  but you can see the end of (1-4)vid.mp4 is getting a little off (the cursor is not all the way to the end, so I guess the video is getting cut off before the end. Not a deal-breaker, since the audio still aligns very well to the video cursor.

  



  Now, since the concatenated video introduces glitchy audio between clips, I want to take the uncut original audio and add that to the assembled video.

  



  ffmpeg -ss 0 -i "(1-4)vid.mp4" -i "origWAV.wav"  -c:v libx264 -map 0:v:0 -map 1:a:0 -c:a aac -ac 1 -b:a 192k -y -vsync 1 -t 12 "(1-4)vid+origWAV.mp4"


  



  but the audio is slightly off now, and ends even further before the end of the video. Since it's really important to align audio and video precisely for this, how can I speed up the video to fit the exact duration of the audio or otherwise fix this issue ?

  


• avcodec/h264 : keep track of which frames used gray references

  16 octobre 2023, par Michael Niedermayer

  avcodec/h264 : keep track of which frames used gray references
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavcodec/h264_picture.c
  • [DH] libavcodec/h264_slice.c
  • [DH] libavcodec/h264dec.c
  • [DH] libavcodec/h264dec.h