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• ffmpeg frame-accurate cutting

  24 septembre 2018, par jvecsei

  I’ve been trying for some time to achieve frame-accurate cuts with ffmpeg.

  Since I don’t want to do a complete re-encoding, my idea was to do a re-encoding only at the intersections. This works fine, but it seems like the sound will become more and more asynchronous over time (at the end 0.5s).

  The command for the intersection point is from the "real" start to the next keyframe :

  ffmpeg -ss 468.24 -to 474.680000 -i input.avi -c:a mp3 -c:v h264 -avoid_negative_ts make_zero -pix_fmt yuv420p -r 25 input.avi_0.tmp.start.avi

  The command for what comes next is from the keyframe to the next cut :

  ffmpeg -ss 479.720000 -t 2039.320000 -i input.avi -c copy -avoid_negative_ts make_zero -pix_fmt yuv420p input.avi_0.tmp.avi

  I do this multiple times and fhe file names of the results will be written to concat.txt

  Then i merge the files with :

  ffmpeg -f concat -fflags +genpts -async 1 -i input.avi_concat.txt -c copy -pix_fmt yuv420p -y input.cut.avi

  Does anyone have any idea what else I can try ? I tried async/vsync but unfortunately without any great result. Before executing the concat command the files are all fine...

• swscale/swscale_unscaled : make the fast planar copy path work with more formats

  15 mars, par James Almer

  swscale/swscale_unscaled : make the fast planar copy path work with more formats
  dst_depth - src_depth where the result is 6 or 7 in a high bd path means this
  
  is only executed for 16 -> 10 and 16 -> 9.
  
  This patch makes this path general, supporting arbitrary formats as long as
  
  dst_depth > src_depth > 8.
  Signed-off-by : James Almer <jamrial@gmail.com>
  

  • [DH] libswscale/swscale_unscaled.c

• Burning subtitles into video with ffmpeg with specific margin not working

  17 mai 2024, par Anthony

  I am trying to build a tool where people can position their subtitles on an HTML5 video and then I will burn the subtitles into the video for them.

  


  I can easily get the position of the subtitles, in whatever format I need, that's easy. However, no combination of values that I feed to ffmpeg are working.

  


  My holy grail is an x and y offest (aka offset 5% from the left, 10% from the bottom, in terms of video height/width).

  


  To achieve this, I would like the subtitles to start in the very bottom-left corner.

  


  ffmpeg -y -i english.mp4 -vf "subtitles=english.srt:force_style='Alignment=1,OutlineColour=&H100000000,BorderStyle=3,Outline=1,Shadow=0,FontName=Arial,FontSize=24,MarginL=140,MarginV=0'"  -c:v libx264 -crf 23 -c:a copy output_video.mp4


  


  Here is something that is approaching working, but it's behaving very strangely. The video is 850x480 but when I do a margin of 140 it goes way past the midway point of the video.

  


  Am I missing something ? How can I start the margin in the bottom left, and then apply the margin I want to push it away from the left and away from the bottom ? I can do it either as a percentage of the video height/width if that API is supported or just pixels is fine too (but clearly doesn't seem to be working)