[mythtv-users] mencoder and re-encoding HDTV shows.
mythtv at rodsbooks.com
Tue Sep 18 14:52:02 UTC 2007
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
> 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.
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