[MPlayer-users] XvMC question

[Ivan Kalvachev]

Hugo Mills said:
> [Automatic answer: RTFM (read DOCS, FAQ), also read
DOCS/bugreports.html]
> On Mon, Nov 24, 2003 at 12:14:10PM -0500, D Richard Felker III wrote:
>> [Automatic answer: RTFM (read DOCS, FAQ), also read
>> DOCS/bugreports.html]
>> On Sun, Nov 23, 2003 at 10:03:35PM -0800, Steven M. Schultz wrote:
>> > [Automatic answer: RTFM (read DOCS, FAQ), also read
>> DOCS/bugreports.html]
>> >
>> > On Mon, 24 Nov 2003, D Richard Felker III wrote:
>> >
>> > > [Automatic answer: RTFM (read DOCS, FAQ), also read
>> DOCS/bugreports.html]
>> > > On Sun, Nov 23, 2003 at 05:17:15PM -0800, Steven M. Schultz wrote:
>> > > > [Automatic answer: RTFM (read DOCS, FAQ), also read
>> DOCS/bugreports.html]
>> > > > Hi!
>> > > >
>> > > > 	Are there extra steps that must be taken to enable and use the
XvMC extension?
>> > >
>> > > XvMC is only useful for playing mpeg1/2. You can't play mpeg4
>> ("divx")
>> > > with it...
>> >
>> > 	So I discovered after experimenting and cranking up the debug level,
and so on.
>> >
>> > 	Is that a "at the moment" (hasn't been implemented yet), a
>> > 	"can not be done" or a "it doesn't make sense" type of "can't"?
>> It's a matter of "can not be done" as in the hardware specifically does
not support it. Remember, the hardware is made for sheep who want to
play dvds rather than for people who want to download free movies.
Actually there are some potential hacks that may allow simple mpeg4
files ("divx4" limits) to be played with the current hardware, but
they're complicated to do.
>
>    Actually, that doesn't answer the question of whether XvMC could be
> used to play MPEG4 through a chip (like the em8400) which *does* have
the capability to decode MPEG4. Is XvMC general enough to handle that,
or is it geared specifically towards MPEG1/2?
>
>    (I should point out that I'm only asking this in a spirit of
> enquiry -- I have no need, or even hardware, for this at present).
>
>    Hugo.
There are 2 problems. I donno how em8400 work, but XvMC work with
exporting
Motion data and DCT blocks to the decoder. If the chip can decode the
stream by itself then it is better ot use another standart.
The other problem is that XvMC is an X extenstion. This way it is very
slowly updated and developed. At the moment the standart defines H263 and
MPEG4 mode, 4MV MacroBlock motion compensation and nothing else. Probably
MPEG4 could default to qarter-pel, but there is no any field for rounding
mode, or method of unrestricted motion vectors (emulated or using blocks
from surface).
Of cource this things will be defined when they begin working on driver
that support h263 or MPEG-4. On the other side why they should write a
driver when nobody uses the exsisting one ... Well there is player now,
and letting your card manifacturer and xfree86 people know that you want
such driver is a good step.
Once there is a driver for some card that can do MPEG-4 I will try to find
the card and develop decoding support for it.

Best Regards
   Ivan Kalvachev
  iive