[mythtv-users] Transcoding HD-PVR Recordings

Bob Sully rcs at malibyte.net
Tue Sep 21 02:33:55 UTC 2010


> Date: Mon, 20 Sep 2010 15:39:33 -0400
> From: Doug Vaughan <r.d.vaughan at rogers.com>
> Subject: Re: [mythtv-users] Transcoding HD-PVR Recordings
>
> John and Kirk,
>      I regularly edit and transcode HDPVR recordings. There are some
> restrictions which may not suit you but here is what I do.
>
> 1) I locked my STB to 1280x720p output. This keeps the recording size
> down but allows me to reliably use a video editor.
> 2) I use a compiled version of Avidemux 2.4 as I found at least the
> Ubuntu packaged version could not handle the audio AC3 tracks. Avidemux
> has not worked for me with 1920x1080i HDPVR recordings. I have reliably
> edited up to 8Gb files if the 1280x720p restriction is adheared to.
> Although I rarely record more than 6Gb HDPVR file.
> 3) I edit the HDPVR recording as needed then save as an avi with copy
> audio and copy video settings.
> 4) I run a ffmpeg copying the audio and video tracks to change the
> container from avi to mkv. This also sets a seek table that reliably
> works with the MythTV internal player.
> 5) If you want to transcode the mkv file use HandBrake either the GUI or
> the CLI. I have several presets for various sizes of transcoded video.
> Handbrake already has iPod presets that you can use. I transcode the
> output to mkv files. If you want to use the cli then you can cut and
> paste their iPod presets from the GUI. That was my starting point when
> building my customized presets.
> 6) Occasionally the audio can be out of sync which I correct with a
> feature of MKV File Creator GUI. MKV File Creator will not accept the
> HDPVR recordings directly you need to at least change their container
> type with a ffmpeg copy.
>
> As I can write python and bash scripts, outside of the manual editing or
> audio resync, the whole process has been automated. I even initiate the
> process as a right click script in Nautilus. The transcoding occurs as
> an overnight cron job.
>
> This would not be what everyone would want but has worked well for my
> needs almost two years now.
>
> Doug

Doug:

This is exactly what I do, with pretty good results.  I do a two-pass
ffmpeg to transcode the HD-PVR file to an .avi, then use avidemux to cut
out the commercials.  Two questions:

(1) No matter how I tweak the HD-PVR settings (right now set to 11M bit
rate), usually a 1-hr raw HD-PVR recording runs about 1.7GB in size (also
at 720p from the STB).  The quality seems VERY good, however.  I would
think that if the bitrate was low that the quality would be poor, but this
isn't the case - but the file sizes imply that it it IS low.  How are you
tweaking your HD-PVR settings?  Mine are set at boot time via the settings
in the wiki.

(2) Step 4:  Can you give us the syntax of your ffmpeg command to convert
your .avi file from avidemux into a .mkv?  I have noticed occasionally
that the audio will be out of sync on playback until I hit the back- or
forward-arrow key, then it's fully in-sync for the remainder of the
playback.

Thanks!
Bob

-- 
________________________________________
Bob Sully - Simi Valley, California, USA
http://www.malibyte.net
http://www.malibyte.com



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