[mythtv-users] transcoding HD material to ease playback

Dan Christensen jdc at uwo.ca
Fri Jan 11 20:39:02 UTC 2008

lemongecko at gmail.com writes:

> On 1/11/08, Dan Christensen <jdc at uwo.ca> wrote:
>> 1) The most obvious thing is to do the scaling ahead of time.
> The video card does that work by way of Xv, if it's available.

I do have Xv.  But I would still imagine that if the source material is
1080p, and with my monitor being 720p, it would advantageous to
downscale ahead of time.  Maybe it's not that important?

>> 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).

I agree that it's not likely to be HD or memory related.  Still, the
more data to be processed, the more cpu time I would expect it to take.

>> 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.

Ok, that's helpful to know.  

> I've thought of doing that, myself. Specifically, deinterlacing. 

Yes, I forgot to mention that.  Even for systems that can play HD
content without stuttering, I could imagine people wanting to do
more sophisticated non-real-time deinterlacing ahead of time.

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

There's no obvious pattern, except that I've noticed more problems with
1080p than 720p.  In general I'm not even sure how to find out stats
about a file, e.g. codec, resolution, bitrate, interlaced/not, etc...


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