[mythtv-users] Lossless cut error - last video segment not included in resulting video file

Doug Vaughan r.d.vaughan at rogers.com
Thu Nov 1 20:41:57 UTC 2012

     Here someinput:

1) With h.264 video encodings I remember reading that Avidemux v2.5x 
tended to cut to the keyframe earlier than what was marked in the GUI. 
Not sure what that meant but I occasionally had to adjust acut where the 
end point caught a bit of a commercial.

2) With mkvmerge "deciding" on which keyframe to cut, the translation 
from a MythTV seek table keyframe to a mkvmerge time code is not 
exact.Lossless Cut calculates to the full ninedecimal digits 
(nanosecond) that mkvmerge can accept. Even at that their may be times 
where mkvmerge is using a keyframe not in-sync with what MythTV had 
determined to be a keyframe.I further speculate that the reason that 
ffmpeg show significantly more video artefacts at cut points is because 
it will only accept six digits of time code decimal accuracy so its 
selection of a keyframe show even more variation.

What would be best is if Avidemux 3.0, ffmpeg and mkvmerge all accepted 
keyframes numbers as cut points along with time codes. Although the 
stable version of Avidemux 2.5x still uses keyframe numbers it cannot 
edit HDPVR h264 1080i recordings and seems to have video file size 
limits. The next releaseof Avidemux 3.0 is resolving those issuesbut has 
switched totime code cut points.

More grist for the grist mill.


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