[mythtv-users] transcoding HD material to ease playback

lemongecko at gmail.com lemongecko at gmail.com
Fri Jan 11 15:36:07 UTC 2008

On 1/11/08, Dan Christensen <jdc at uwo.ca> wrote:
> I've got a frontend/backend that is just barely able to play some HD
> material:  it's a 32-bit single-core mobile Athlon at 1.9GHz, with an
> FX5200 video card.  I was surprised that it can play HD material at all,
> but it does fine on most of the sample clips I've downloaded, using
> 60-80% cpu.  (I'm not using xvmc.)  However, in a few cases it is not
> able to play the HD sample.  So I thought that I could transcode such
> material into a format that requires less cpu to play:
> 1) The most obvious thing is to do the scaling ahead of time.  My
> HDTV has non-square pixels, so almost all material needs scaling,
> and I'm guessing that this will help a lot.  Or does the video card
> do all of that work??

The video card does that work by way of Xv, if it's available.

> 2) I wonder if lowering the bitrate a bit might help?

Nope. Not unless your playback issues are due to an I/O limitation in
memory (which is doubtful).

> 3) What codec should I use?  I'm not too concerned about disk space,
> as these are just short clips I'm playing with to see how my HDTV
> looks.

Stick to MPEG-2. It's very cheap computationally and it gives you the
path to try out XvMC if you so choose.

> Comments, and even specific command lines, are welcome.

I've thought of doing that, myself. Specifically, deinterlacing. 720p
content is pretty easy for a machine to do. The kicker is interlaced
content. Setting up a transcode job that deinterlaced and also scaled
the frames down a bit would go a long way to helping borderline

The files that you could NOT play cleanly... in what way were they
different from the ones that DID play?

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