[mythtv-users] Lossless Cut (mythcommflag vs mythtranscode)

[Doug Vaughan]

Angela,
     Here is some information about how the Lossless Cut scripts work 
with MythTV's seektable.

1) The seektable is used to estimate the excact time (duration) into the 
video where a cut should start or end. (seektable keyframe * frames per 
second).
2) The calculated cut point in time (HH:MM:SS.nnnnnnnnn) is passed to 
mkvmergeduring the cut process. mkvmerge itself determines the nearest 
actual keyframe in the video source correspondingto the given time and 
makes the cut.

If there is any inaccuracy between the datain the seektable and/or how 
mkvmerge interrupts the video source the cut pointwill be inaccurate. In 
a large way theLossless Cut scripts are a major hack but it was the only 
way I found, when the scripts where written, to utilize Myth's 
commflagging, cutlist editor and creating lossless cut recordings for a 
HDPVR recording device.

It was pure happenstance that the scripts worked with recordings made by 
other recording devices.The accuracyof the lossless cuts points will 
only get better if mkvmerge improvesbut the fact a translation between 
MythTV's data and mkvmerge's own keyframe determination means it will 
never be perfect. For example, mkvmergecannotaccurately handle variable 
bit rate recordings (e.g. HDHomerun). That eliminates a whole series of 
recording devices.

Doug