[mythtv-users] Lossless Transcoding problems - Is it solvable or are there other options ?

[John Pilkington]

On 10/10/13 17:52, John Finlay wrote:
> On 10/10/2013 5:31 AM, Chris Gaskell wrote:
>> I've just moved from 0.24 to 0.26 and am finding the same issues as
>> others have found with lossless transcodes.  I'm using mythtranscode
>> to cut commercials and the end of the preceding programme. I had no
>> problem in 0.24 so this is pretty frustrating.
>>
>> Using 0.26.0 lossless transcodes failed completely. After reading
>> previous comments I updated to 0.26.1 and found lossless transcodes
>> worked, but I lose the first few seconds of audio and according to the
>> playback info, it thought my 45 minute programme lasted 26+ hrs!
>> Furthermore, playback crashes if I try to skip forwards. I've not
>> tried it yet but I believe vlc and handbrake also don't work properly
>> with these files so it's all a bit unsatisfactory.
>>
>> From other threads, it seems the problems I'm seeing are a known
>> issue.  Is there any way to fix it, or can anyone recommend another
>> way of lossless commercial removal?  I'm no whizz from a terminal so
>> would like a fix that I can use from inside mythtv - maybe a user job
>> that calls ffmpeg ?
>>
>> Can anyone give some advice to get better results ?
>>
> I think that 0.27 lossless cut transcoding may work better for playback
> in mythtv than 0.26 transcoding but I still get a few missing seconds of
> sound at the beginning though seeking seems to bring the sound back. But
> when using the transcoded file as input to mythffmpeg, avconv, vlc or
> handbrake I do not get good results. In the best case the reported
> duration is wrong sometimes wildly wrong (e.g. 27h for a 30m video) and
> in the worst case handbrake and ffmpeg seem to hang until I kill the
> process. The response that I got from Mike Dean could be interpreted to
> mean that no developer is actively looking into the post-processing
> problems so I am also looking for an alternative. I have been using 0.27
> mythffmpeg to cut commercials with some success as long as I cut on
> keyframes only but the cuts are not accurate which my be a limitation of
> mythffmpeg or the mythtv editing process. At least the resulting files
> can be post-processed by avconv, ffmpeg and handbrake.
>
> John

I don't know what format your recordings come in, but I find cutting at 
keyframes works pretty well with most dvb-t (SD) channels in the UK, at 
least for cutting at start, end, or ad-breaks.  If you're wanting fine 
editing elsewhere in the recording you might well need something better. 
  And the setting of edit-points got much easier when I introduced a 
few-frame offset between the (key)-frame-number derived from the cutlist 
and the byte-offset passed to Project-X.  mythDVBcut. YMMV.

Sometimes keyframes in dvb-t2 (HD) recordings are apparently very widely 
separated.  ISTR seeing very few in one programme on the BBC HD 
RedButton channel 303.

John P