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• Generate animated padded thumbnail using ffmpeg

  15 juillet 2022, par kregus

  we've been generating animated thumbnails with ffmpeg without a problem using this command :

  


  ffmpeg -y -ss 5 -t 3 -i "/input.mp4" -i /playbtn.png -r 10 -filter_complex "[0]fps=10,scale=1280:-1:flags=lanczos[pb];[pb][1]overlay=(W-w)/2:(H-h)/2, split[s0][s1];[s0]palettegen=max_colors=32[p];[s1][p]paletteuse=dither=bayer" /output.gif


  


  However, now we want to force each thumbnail to be 1280x720 and pad the rest black.

  


  This works well for regular thumbnails with this command :

  


  ffmpeg -y -ss 5 -t 3 -i "/input.mp4" -vframes 1 -filter:v "scale=w=1280:h=720:force_original_aspect_ratio=1,pad=1280:720:(ow-iw)/2:(oh-ih)/2" /output.jpg


  


  Now I tried dozens of ways to try and integrate the force_original_aspect_ratio and pad filters into the animated thumbnail generation code, but am getting a host of errors, like :

  


  Cannot find a matching stream for unlabeled input pad 0 on filter Parsed_split_4

  


  When I tried this command :

  


  ffmpeg -y -ss 5 -t 3 -i "/Users/nick/Downloads/intro_portrait_nl_1650909779_rendereddd.mp4" -i /Applications/Ampps/www/vormats_aws/web-render/functions/files/playbtn.png -r 10 -filter_complex "[0]fps=10,scale=1280:720:flags=lanczos:force_original_aspect_ratio=1,pad=1280:720:(ow-iw)/2:(oh-ih)/2[pb];[pb][1]overlay=(W-w)/2:(H-h)/2;split[s0][s1];[s0]palettegen=max_colors=32[p];[s1][p]paletteuse=dither=bayer" /Users/nick/Downloads/smallLandscapeee.gif


  


  ... You get the point, I have no idea how to adapt our original animated thumbnail generation code to force a 1280x720 resolution with padding.

  


  Any input is appreciated, thanks !

  


• Why does FFMPEG b-frames and b_pyramid offset start_pts (and start_time) in fragmented output ?

  13 juillet 2022, par Vans S

  It seems when transcoding something into fragmented or segmented output the start_pts is not 0, and no combination of options can make it 0 other than setting bframes to 0 and bpyramid to 0. This does not happen with regular nonfragmented output.

  


  Does anyone know why this is, and how to prevent it as I believe this is causing weird timesync issues with playback in browsers (every fragment slightly delays the video more and more) where after 2-3 hours the stream can end up 15minutes+ delayed.

  


  Example where each segment start_pts is not 0 :

  


  ffmpeg -i in.mp4 -pix_fmt yuv420p -an -f yuv4mpegpipe -frames:v 150 - | ffmpeg -f yuv4mpegpipe -i - -y -force_key_frames 1,2,3,4 -map 0 -codec:v libx264 -f segment -segment_list out.csv -segment_times 2,4 -segment_time_delta 0.05 -preset:v fast -segment_format_options movflags=+faststart out%03d.mp4


  


  start_pts is 0 here if we add :

  


  -x264opts b_pyramid=0 -bf 0 
#or change codec to
-codec:v mpeg4
#or output regular mp4
ffmpeg -i in.mp4 -pix_fmt yuv420p -an -f yuv4mpegpipe -frames:v 150 - | ffmpeg -f yuv4mpegpipe -i - -y out.mp4


  


  EDIT : Looking into this further I am starting to think this is a bug with how empty_moov interacts with the negative_cts_offsets flag. (when empty_moov is used, negative_cts_offsets seems to be ignored, and we need empty_moov for full webbrowser support.)

  


• Why does FFMPEG b-frames and b_pyramid offset start_pts (and start_time) in fragmented output ?

  13 juillet 2022, par Vans S

  It seems when transcoding something into fragmented or segmented output the start_pts is not 0, and no combination of options can make it 0 other than setting bframes to 0 and bpyramid to 0. This does not happen with regular nonfragmented output.

  


  Does anyone know why this is, and how to prevent it as I believe this is causing weird timesync issues with playback in browsers (every fragment slightly delays the video more and more) where after 2-3 hours the stream can end up 15minutes+ delayed.

  


  Example where each segment start_pts is not 0 :

  


  ffmpeg -i in.mp4 -pix_fmt yuv420p -an -f yuv4mpegpipe -frames:v 150 - | ffmpeg -f yuv4mpegpipe -i - -y -force_key_frames 1,2,3,4 -map 0 -codec:v libx264 -f segment -segment_list out.csv -segment_times 2,4 -segment_time_delta 0.05 -preset:v fast -segment_format_options movflags=+faststart out%03d.mp4


  


  start_pts is 0 here if we add :

  


  -x264opts b_pyramid=0 -bf 0 
#or change codec to
-codec:v mpeg4
#or output regular mp4
ffmpeg -i in.mp4 -pix_fmt yuv420p -an -f yuv4mpegpipe -frames:v 150 - | ffmpeg -f yuv4mpegpipe -i - -y out.mp4


  


  EDIT : Looking into this further I am starting to think this is a bug with how empty_moov interacts with the negative_cts_offsets flag. (when empty_moov is used, negative_cts_offsets seems to be ignored, and we need empty_moov for full webbrowser support.)