[mythtv-users] Best HD transcoding setup & settings?

Steven Adeff adeffs.mythtv at gmail.com
Thu May 24 15:42:28 UTC 2007


On 5/17/07, Richard Freeman <r-mythtv at thefreemanclan.net> wrote:
> Joe Borne wrote:
> > Bryan Mayland wrote back:
> >>I have the following common settings:
> >>Lossless Transcoding NOT checked
> >>Resize Video while transcoding NOT checked
> >>Codec: MPEG4
> >>Scale bitrate for frame size NOT checked
> >>Enable high-quality encoding checked
> >>Enable 4MV encoding checked
> >>(I believe the sound settings aren't used currently)
> >>For 1080i I use Bitrate=3500
> >>For 720p I use Bitrate=2500
> >>For 480i I use Bitrate=1500
> >>For both interlaced profiles, I have "Enable interlaced DCT encoding"
> >>and "Enable interlaced motion estimation" checked.
> >>
>
> You mention that the sound settings aren't used.  Will there be any way
> in the future to preserve an AC3 soundtrack when transcoding HD?  I've
> been trying for ages to find a reliable way to transcode HD to SD while
> preserving the sound - I only have an SD TV but I'd like to capture the
> AC3 audio.  The problem is that I can't seem to generate a video stream
> that myth's internal player can handle - they play fine unless you try
> to seek in any way (even after rebuilding the seektable).  Part of the
> issue may be defects in the original HD recording (I don't get
> completely perfect reception, so there are glitches in the recorded
> stream) - but the original recordings seek fine with the internal
> player, so it should be possible to transcode them.
>
> What I'd like to do is preserve the AC3 soundtrack while dropping the
> resolution to 480 lines.  The best I've come up with is:
>
> if mencoder -o /dev/null $1 2>/dev/null | egrep -q 'fps:(59|60)'; then
>     # progressive
>     OFPS="30000/1001"
>     FPS="60"
>     FILTER="tinterlace=4,scale=720:360:1,expand=:480"
> else
>     # interlaced
>     OFPS="30000/1001"
>     FPS=$OFPS
>     FILTER="scale=720:360:1,expand=:480"
> fi
>
> nice mencoder -of mpeg -mpegopts format=mpeg2:vbitrate=2000 -oac copy
> - -ovc lavc -lavcopts vcodec=mpeg2video:vbitrate=2000:keyint=18:aspect=4/3
> - -vf $FILTER -fps $FPS -ofps $OFPS -vc mpeg12 -o /var/video/$1.tmp
> /var/video/$1
>
> (And various parts of that are borrowed from this list.)
>
> I'd actually prefer something better then MPEG-2 and a lower bitrate but
> I figured I should walk before I run...

http://www.mythtv.org/wiki/index.php/User:Steveadeff#HR.HDTV_script

-- 
Steve
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