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

[John Finlay]

On 10/10/2013 11:06 AM, John Pilkington wrote:
> 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
My recordings are US OTA so are generally HD mpeg2 in mpegts. I use the 
cutlist frame info from mythtv to slice the file up using mythffmpeg and 
then reassemble the bits I want to keep. Looking at the result it 
appears that mythffmpeg makes the keeper sections one keyframe longer 
than the specified cut end. I'll try specifying one keyframe less and 
see if that works.

John