[mythtv-users] [Bulk] lossless cut question

Doug Vaughan r.d.vaughan at rogers.com
Fri May 17 01:06:23 UTC 2013


On 13-05-16 07:40 PM, glen wrote:
> i am trying to use the scripts for hdpvr recordings only. on each 
> occassion the resulting mkv loses audio sync gradually. on a 42 minute 
> show, it is off -300ms everytime by the end.
>
> if i look up the cutpoints in mythconverge, and manually calculate the 
> timecodes and use the mkvmerge gui, and use 'split in parts based on 
> timecodes', the resulting mkv is alway in sync. are there any changes 
> i can make to the script to get the same result from the script ?
>
> thanks for any help.
>
> using latest mkvmerge, on mythbuntu (precises) and 0.25 fixes.
Glen,
     Although I use 0.26 fixes I do remember that the majority of v0.25 
hdpvr recordings had a time sync issue of 300-340ms. Back then Iwas 
manually cutting commercials with Avidemux2.5xand had to use mkvgui to 
correct the sync issue. I never experienced majoraudio sync drift issues 
as you described.

My own experience with Lossless_cut and hdpvr 0.26 recordings over the 
last severalmonths has been that some cut recordings have aconsistent 
audio sync issue of 150ms (audio needs to be delayed). It is infrequent 
but happens. I correct the cut video with mkvgui to apply an audio delay.

The only gradual audio drift I've noticed was with cut recordings longer 
than 2hrs where the original recording duration was 3hrs+. Therefore 
many cuts are required to pare it down to ~2hrs.The drift was slight 
enough that it was tolarable. There is a special mkvmerge command line 
variable you can use to compensate for gradual drift but Inever tired is 
myself. From what I remember it is only meantfor slight drift over a 
long time not forwhat you describe.

I certainly cannot guarantee that upgrading to MythTV v0.26 fixes will 
resolve this issue but that version includes a number of 
improvements/fixes related to h264 encoded videos.

Sorry I do not have any other suggestions at this time. My testing of 
Lossless_Cut with MythTV v0.25 did not reveal this issue but I was using 
hdpvr recordings that were originally made by MythTV v0.26as I have a 
limited test environment. Maybe that accounts for the dependencies.

Doug


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