[mythtv-users] Transcoding overhead, could use some advice...

[James L. Paul]

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On Sunday 14 December 2003 09:54, Curtis Wood wrote:
>    Is there anyway to speed up the process of transcoding, currently it
> is taking hours to transcode. a 2hr movie transcoded to the highest
> format is taking from 4-6+ hours to finish. Im running the backend and
> frontend  on the same machine, while it is transcoding I can't record -
> let alone transcode another recording (other wise the frontent locks
> up)... I realize that this may be a CPU intensive task (which it is,
> jumps the load up to 3.0-5.0) - but it doesnt seem to make a difference
> (in time) whether anything else is running or not, as in watching live
> tv...

The transcoding is indeed CPU-bound. The compression ratio affects transcoding 
time somewhat, but in general you aren't going to dramatically reduce your 
transcoding time without a lot more CPU. Your processor is crunching as fast 
as it can, end of story. You can only make it faster by asking it to do less, 
and that involves significant tradeoffs when if comes to compressing video in 
software on a general purpose CPU.

What I'd love to see is a way to use hardware encoders like the PVR-250 for 
transcoding, and even then we would have the overhead of software decoding to 
feed the encoder for transcoding. Ahh well. :)

I don't do a lot of transcoding with mythtranscode, but I assume there's a bug 
that prevents you from transcoding in the background while recording. There's 
no inherent reason I'm aware of that should cause this problem. The 
transcoding threads should be the lowest priority, so sorry to hear you are 
having lockups. Perhaps fixing that problem will make living with transcoding 
easier.

Myself, I chose to avoid transcoding as much as possible. The PVR-250 cards 
really take burden off the CPU and I can avoid encoding by recording directly 
to a format that is very versatile. I know that may not apply to your 
situation, but the cost of the cards was way lower for me than the cost of my 
time in working around the issues of not having hardware encoding. :)

My advice: try to reduce your need to transcode for common use. If that's not 
an option, add more or faster CPU. At the very least try to solve your lockup 
issue so that transcoding does not interfere with normal recording. And good 
luck!

>    Im running everything on a P4 2.4 ghz, 256mg ram (could be an issue),
> all on top of GenToo... Im still on 0.12, waiting for the transcoding to
> finish so I can compile 0.13 - its been processing since 7:30 this
> morning (roughly 7hrs)...
>
> TIA,
> Curtis
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