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• ffmpeg get last x seconds with high accuracy

  12 mars 2018, par rbarab

  I would like to batch process mp4 videos, getting the last x seconds of each and saving them to individual files.
  I need to do this with a very high accuracy, preferably to 0.001 seconds or better.
  Found a related question (FFMPEG : get last 10 seconds) suggesting -sseof, which works great, but as the answer said it’s not completely accurate with stream copy.

  I am trying to match video lengths to the length of a reference video.

  Would I need to re-encode ? Can sseof handle this accurate enough if I specify duration as 00:00:00.000000 (which I get from reference video ffprobe) ?

  Please see related ffprobe -i below, all videos to be processed have this same encoding.

     Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf57.83.100
  
    Duration: 00:00:58.67, start: 0.000000, bitrate: 639 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360, 499 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 59.94 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 131 kb/s (default)
  
      Metadata:
  
        handler_name    : SoundHandler
  
  duration=58.673000

  Is there a better way to achieve frame-level accuracy ? As end goal I would need to overlay these videos with 25fps ’frame-level accuracy’.

  Thanks a lot !

• vp9 : split superframes in the filtering stage before actual decoding

  13 novembre 2016, par Anton Khirnov

  vp9 : split superframes in the filtering stage before actual decoding
  Significantly increases the efficiency of frame threading, since
  
  individual frames in a superframe can now be decoded in parallel.
  

  • [DBH] configure
  • [DBH] libavcodec/vp9.c

• FFMPEG Generate video clips and concatenate them all

  8 février 2020, par lms702

  I have a bunch of images (.png) and audio files (.wav) that I want to combine and concatenate. For example, if I have a1.wav, i1.png, a2.wav, and i2.png, I want to output a video that is a1.wav overlayed onto i1.png, then (concatenated to a2.wav overlayed onto i2.png.

  Currently, my approach is to save each individual clip and then concatenate them all at the end.

  To save each clip, I use this command (in a loop for all of my clips) :

  ffmpeg -i {imageFile} -i {audioFile} -nostdin -qscale:v 1 -vcodec libx264 -pix_fmt yuv420p {outputFile.mp4}``

  It outputs an mp4 that kind of works - the playback is really buggy but works in full screen.

  My current approach to concatenating has not been at all successful. I create a list of the clip names and put it into filename then call this command :

  ffmpeg -f concat -i {filename} -c copy clips/finalOutput.mp4

  This outputs a pretty jumbled video and this error repeated :

  [mp4 @ 000001cdec110740] Non-monotonous DTS in output stream 0:1; previous: 1045041, current: 604571; changing to 1045042. This may result in incorrect timestamps in the output file.

  So, a few questions.

  What is the best way to go about this process ?

  Should I be saving each clip or is there a better way to do it all in one command ?

  If I do save each clip, is there a better file format I should use ?

  Plz help with the concatenation command.

  Also note that because I am automating this with python I can build arbitrarily large commands, though that might not be ideal.

  I am very new to this and I would really appreciate any help !