[mythtv-users] Alternatives to lossless transcode

Paul Gardiner lists at glidos.net
Tue Nov 26 09:51:11 UTC 2013


On 25/11/2013 21:39, Mark Perkins wrote:
>
>
>  > Date: Mon, 25 Nov 2013 09:53:51 +0000
>  > From: lists at glidos.net
>  > To: mythtv-users at mythtv.org
>  > Subject: Re: [mythtv-users] Alternatives to lossless transcode
> ...
>  > The cleancut option doesn't alter the cuts. The same sections of audio
>  > and video will be missing from the fifo streams as without the option.
>  > It changes only the internal mechanism by which mythtranscode achieves
>  > the cuts. Without the cleancut option, mythtranscode gets mythplayer
>  > to perform a seek from the start of the cut to the end. That can lead
>  > to a moment of audio and video being slightly out of sync. Mythtranscode
>  > quickly corrects the sync, but there can be a noticeable hiccup. With
>  > the cleancut option, mythtranscode performs the cutting by seeking to a
>  > point a little before the end of the cut, and then dropping audio and
>  > video until the true end of the cut is reached.
>  >
>  > Paul.
>  > _______________________________________________
>
> Thanks Paul. Hope you don't mind me asking a few more questions - but
> I'm not hugely familiar with the workings of ffmpeg. In Handbrake I had
> presets set to default for deinterlacing and detelecine because as my
> recordings are OTA TV I don't really know if any particular recording
> will be interlaced / telecine or not or and apparently the defaults were
> pretty harmless in the cases that they weren't needed and did a good job
> in the cases where they were needed.
>
> Do I need to be looking into deinterlacing / detelecine for ffmpeg or
> does this fifo method just take all of this into account and "sort it out"?
>
> I think Handbrake and ffmpeg both use x264 for the actual processing but
> I couldn't find anywhere that would translate Handbrake settings into
> equivalent ffmpeg settings.

ffmpeg may have a similar deinterlacing method which is applied only if
needed. I haven't looked, because my intention in the script was to
improve on the results I achieved with Handbrake, at the price of having
to specify whether the source is interlaced or not. The problem with
deinterlacing (as Handbrake does it) is that it effectively halves the
frame rate and makes the motion much less smooth. You'll notice this
only if the source is truly interlaced (live shows, sports, dancing,
whereas dramas and films are invariably progressive). What I've done in
the ffmpeg script is give the option to maintain the interlace, avoiding
deinterlacing artefacts and keeping the smooth motion. The only case
where the script uses a deinterlacer is when scaling 1080i content
down to 720, but even then it keeps the smoothness because it uses
a 2x deinterlacer and doubles the frame rate (doubling the frame rate
adds only a little to the size of the resulting file). When I last used
Handbrake - some time ago - it didn't have an option to maintain
interlace.

Cheers,
	Paul.


More information about the mythtv-users mailing list