[mythtv] H.264 and mythtv
Michael T. Dean
mtdean at thirdcontact.com
Wed Aug 31 17:48:09 UTC 2005
Bernd Paysan wrote:
>Hi,
>
>heise.de reports that from October, 26, two free-TV programs are going to be
>send in HDTV quality (1080i) in Germany:
>
>http://www.heise.de/newsticker/meldung/63402
>
>However, they'll use H.264, not MPEG-2. AFAIK, ffmpeg can already decode
>H.264.
>
>Are there any plans to include H.264 support into mythtv?
>
>
(I can't read German, but it looks to me like they're talking about
high-def resolutions...)
Note, however, that even top-of-the-line x86-based (including
AMD64/EMT64) chips can not keep up with H.264 decoding at high-def
resolutions (even 720p) with acceptable frame rates. Microsoft lists
minimum requirements
(http://www.microsoft.com/windows/windowsmedia/content_provider/film/ChoosingPC.aspx
) that in truth are way too optimistic--even with Windows drivers
providing full support for all (sound/video) card features.
MacOS X on top-of-the-line PPC is able to decode H.264 at 1080i at 24-30fps
iff it's QuickTime H.264. Similarly, Windows machines have a hard time
with QuickTime H.264, but perform much better with WMV H.264. (Perhaps
some optimization or even reverse-optimization for the platform's
preferred codec?)
For H.264 in high def, we really need dedicated silicon to do the
decoding--especially if the CPU is doing other things. The ATI R520
will have dedicated silicon to handle H.264 decoding (to be released
sometime in October, probably), but whether there will be support for it
in the Linux drivers (considering today's ATI drivers don't even have
XVMC support) and whether there will be a standard API for using it
(don't know of any at this point), is unknown. NVIDIA cards will not
have the H.264 decoding built in.
However, another (more portable?) option is using OpenGL 2.0's GLSL with
relatively-recent ATI and NVIDIA cards to use the programmable shaders
for video decoding (semi-dedicated silicon). This approach is less
efficient than using dedicated silicon, but portability at the expense
of efficiency is probably worthwhile. Note that this requires
relatively recent cards since older cards do not allow enough
instructions for the PS to allow the GPU to do the decoding. (Does
ATI's Linux driver provide OpenGL 2.0 support? NVIDIA's first to
support 2.0 was 7664.
http://www.nvidia.com/object/linux_display_ia32_1.0-7664.html )
Remember when we used to have hardware DVD decoders? They're back with
H.264...
If any ATI/NVIDIA guys want to provide me with a card, I'd be happy to
add GLSL support to Myth. :)
Mike
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