[mythtv-users] mencoder and re-encoding HDTV shows.

[Rod Smith]

On Tuesday 18 September 2007 04:30:46 jack snodgrass wrote:
> I'm using this mencoder command to re-encode a HDTV show to something
> smaller... something
> I can stream to my office over the internet or something I can put on
> a usb drive....
>
> mencoder -srate 22050 -vf scale=720:400 -oac mp3lame -lameopts
> preset=15:mode=3 -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=900 -sws 2
> -o /tmp/1005_20070914190000_720x400x900.avi
> /mnt/store/1005_20070914190000.mpg
>
> This command takes 22 minutes or so to re-encode a 30 minute,
> .... this 
> is on a E6600 Core Duo.
...
> Does anyone have any suggestions for alternatives to my mencoder setup
> that will be a lot
> faster and give me similar results?

I doubt if you'll be able to speed up that transcoding job by much, at least 
not without upgrading the CPU. HD content is BIG, and scaling it involves 
computations; it's not just a matter of discarding every other byte or 
anything simple like that.

That said, I do have a couple of suggestions:

1) You could use -oac copy rather than -oac mp3lame. (You'd also then
   discard the -lameopts options, too.) This will copy the original's
   audio track rather than re-encode the audio. In theory this should
   be faster, but compared to the video re-encoding, the audio re-encoding
   shouldn't be taking a lot of time, so I doubt if you'd cut the time by
   more than a couple percent. I'm not positive an MPEG-4 file would be
   happy with audio copied directly from an HD broadcast, though.

2) You could try a format other than MPEG-4 for the final format. MPEG-4
   is a CPU-intensive format, so you might be able to save a bit of time
   by encoding to MPEG-2 or RTJpeg; however, this will also result in
   bigger files and/or lower quality. If you go this route, you might
   actually get better results by going with slightly lower resolution
   than the 720x400 you've specified.

-- 
Rod Smith
http://www.rodsbooks.com