• Compression Techniques

  editing mov files without recompression

  Posted by Grzegorz Kwiatkowski on August 24, 2013 at 7:30 am

  Hi,

  is there any intuitive way that can do insert edits with no recompression in mov files? I am delivering Avid DNxHD mov files for broadcast and this would save me much time. Ahhh… and I am looking for something with graphical GUI.

  Thanks

  Reuben Martin replied 12 years, 8 months ago 3 Members · 2 Replies
• 2 Replies

• 

  Jim Sustacek

  August 27, 2013 at 1:03 pm

  I don’t know anything about the Avid DNxHD codec, but if you have the codec installed and QuickTime Pro can open the files, I would use that to identify your edit points (GUI). Then, assuming FFMPEG can decode/encode that codec, you could use that to do the actual editing (no GUI).

  When trimming segments, if you are simply copying the Avid DNxHD codec (no re-encoding), you may have to begin your trim segments on keyframes — at least that is what I have to do with H.264:
  https://trac.ffmpeg.org/wiki/Seeking%20with%20FFmpeg

  If that’s the case, use ffprobe to find keyframe locations:
  https://stackoverflow.com/a/14013439/2096063

  Otherwise, you could do a “Lossless H.264” transcode when cutting all of your segments, then you shouldn’t lose quality nor have to worry about keyframes — see here:
  https://trac.ffmpeg.org/wiki/x264EncodingGuide

  And finally, if your edit segments all have the same codecs and settings, you should be able to use the “concat demuxer” referenced at the following link to join them without re-encoding:
  https://trac.ffmpeg.org/wiki/How%20to%20concatenate%20(join,%20merge)%20media%20files

  Ultimately, if you went the Lossless H.264 route, you’d eventually have to encode it back to non-lossless so it could be read by other programs. I’ve found “-crf 18” is a great-looking libx264 encoding option.
• 

  Reuben Martin

  September 9, 2013 at 10:55 pm

  In theory, you can chop up itra-frame codecs (such as DNxHD) and splice them together without re-encoding. Codecs with I-P-B frames can only get cut on an intra frame. (a.k.a. key frame) In practise it’s more complicated than that since video frame timestamps have to be updated. So the ability to do that depends on the capability of the software. You should be able to do that with ffmpeg. However, if you’re looking for something with a GUI, you’re in the wrong place.

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