[mythtv-users] Lossles Cut marking recordings as "Transcoded"

[Anthony Giggins]

On 26 March 2016 at 05:52, HP-mini <blm-ubunet at slingshot.co.nz> wrote:

> On Thu, 2016-03-24 at 10:07 +0000, Stuart Auchterlonie wrote:
> > On 23/03/16 03:10, Anthony Giggins wrote:
> > > This hasn't been a problem until recently but due to h.264 channels
> > > being pushed out in AU, I can no longer use the inbuilt mythtv
> > > transcoding for this recordings, I've
> > > found https://www.mythtv.org/wiki/Lossless_Cut which works but does
> not
> > > mark these recordings as "Transcoded" in the database, while I can
> > > manually mark these are recorded in the database I'd rather use a
> > > approved method (API or utility) is there any current API function or
> > > util that can do this?
> > >
> > > or even better has the inbuilt transcoder been updated (perhaps in
> > > master) to handling h.264?
> > >
> >
> > Unfortunately not. It's on the todo list, but nobody has yet implemented
> > lossless transcoding for h264 recordings :(
> >
> > I'd love to see it to, having far to many childrens shows in HD with
> > extra data i can't remove at this time
> >
> >
> > Regards
> > Stuart Auchterlonie
> > MythTV Developer
> >
> > _______________________________________________
>
> The beauty of transport streams & h264 is that transcoding can be
> avoided (unless you must use H265!).
> Non-transcode Cutting a 1 hour (5GB) file only takes 1-2 minutes on a
> core2duo while using cutlist editor on another file.
>
> Off topic background on LosslessCut..
> When it was first released it didn't get much attention outside of
> HD-PVR (US) because mkvmerge (mkvtoolnix) couldn't handle LATM AAC which
> is normally used with broadcast H264.
> Mkvtoolnix added LATM AAC support in Jan 2015.
> A user job script to remux LATM AAC to AAC was simple enough.
> Some effort was required to get mythtv's H264Parser frame/byte/usec
> accurate.
>
> OTA Broadcast streams have the audio data delayed w.r.t. video data to
> allow time for video post processing in memory weak devices.
> It can be seen that recording starts playback in VLC with audio & no
> video (for split second).
>
> Mkvmerge cuts at the keyframe on or after the chapter or timecode.
> Mkvtoolnix's "time zero" is the lowest time stamp found in stream which
> will be an audio packet with broadcast (& typically 0.5sec before
> video).
> MythTV's "time zero" is first video packet & should be keyframe if use
> Start-on-SEQ/SPS.
> It's fairly obvious how this can result in inaccurate cutting but it
> should be soluble by probing file for AV packet offset with mediainfo /
> ffprobe / mkvinfo? & adjusting the cut times for mkvmerge.
>
> I believe the author never saw this problem because of using HD-PVR
> device.
>
>
FYI, I hacked a simple solution into the lossless cut script
/usr/bin/lossless_cut

I just added the below after the $LAUNCHER $* line
echo "update recorded set transcoded = 1 where basename like '%.mkv';" |
mysql -uUSERNAME -pPASSWORD mythconverg

please note you'll need to replace your username and password to the mysql
database to make this work, please use at your own risk :)

Cheers,

Anthony
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