[mythtv-users] Transcoding and H264

Christopher Meredith chmeredith at gmail.com
Sun Jan 30 22:07:37 UTC 2011

On Sun, Jan 30, 2011 at 1:17 PM, Jeffrey J. Kosowsky
<mythtv at kosowsky.org> wrote:
> I have been a longtime user of mythtranscode/mpeg4 which I use to
> transcode my OTA mpeg2 recordings to mpeg4 compressed down to
> 1-1.5GB/hour.
> However, given the current problem with 6 channel transcoding plus the
> general sense that mythtranscode is long in the tooth and lagging
> H264, I am interested in switching to H264 transcoding.
> I have several questions:
> 1. In general how much slower will H264 *encoding* be relative to
>   mythtranscode Mpeg4? (I have an old/slow machine and slow graphic card)
> 2. Similarly, how much slower will *decoding* be?
> 3. Are there any plug-ins available to automate such transcoding?
> 4. If not are there Job scripts and instructions available?
>   (note: I checked http://mythtv.org/wiki/Category:User_Job_Scripts
>   but didn't see much other than "Transcode wrapper stub" which
>   seemed to only be part of the solution)
> 5. What is a "reasonable" bandwidth expectation for good quality H264
>   in 1080 and/or 720p?
>   (Note with mp4 I was using 1-1.5GB/hour. What type of quality can I
>   expect with H264 in that bandwidth range?)
> Basically, I would like something that will automatically transcode
> all new digital recordings to H264 with some ability to set the
> bandwidth/disk space used. If it is a script, I want to be able to
> either manually or automatically start it and then have the script
> take over to launch the right transcoding codec, do the transcoding,
> remove the original when done, and then update the mythdatabase when
> done.
> Sorry if any of my questions seem too newbie but I just am not
> experienced in this and I *know* that others must have solved this
> problem many times over.

H264 takes a lot of horsepower, especially in HD resolutions. My old
BE was a P4 3.4 and when transcoding to 720p H264, I'd get about 4-5
FPS. Now that I'm using a dual core AMD, it's about 10-12 FPS. And
decoding is not even a factor if you have a VDPAU-compatible gfx card.
Otherwise, it's probably impossible. The P4 couldn't do it.

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