[mythtv-users] XvMC and libmpeg2 to be dropped in 0.25

James Courtier-Dutton james.dutton at gmail.com
Sun Dec 5 14:33:38 UTC 2010

On 2 December 2010 19:05, Robert McNamara <robert.mcnamara at gmail.com> wrote:
> We'd like to warn users that we are planning to drop XvMC and libmpeg2
> decoding support from forthcoming MythTV releases. MythTV 0.25 will be
> the first release without these features, so you still have several
> months to upgrade hardware if you wish to continue running the latest
> MythTV releases. Of course the newly released 0.24 will remain
> available if either XvMC or libmpeg2 are important to you.
> Why are we doing this?
> XvMC - The primary reason is that the XvMC code is very hard to
> maintain. It requires a lot special handling and does not support the
> features which many of our other video rendering methods provide. Far
> superior alternative hardware decoders such as Nvidia's VDPAU are now
> supported. Crystal HD, ATI and Intel support are also on the MythTV
> roadmap.
> libmpeg2 - A high proportion of problems reported to us can be traced
> back to libmpeg2, we want MythTV to be as stable as possible and the
> advantages of libmpeg2 are outweighed by the negatives. Like XvMC, it
> complicates the code in ways that make it harder to maintain.

You say that you wish to use ffmpeg for mpeg2 decoding instead of libmpeg2.
Although I have not looked at ffmpeg mpeg2 support recently, it was
way behind libmpeg2 performance wise and feature wise.
For example, there was no way to get ffmpeg to play DVD still menus,
it did not have the api required for that.
For example, sending a single I-frame to libmpeg2, libmpeg2 is able to
display it onto the screen immediately, ffmpeg only does this after
other frames have arrived in the buffer.
So, I am only highlighting some issues you might not be aware of,
particularly if myth is able to play DVDs.

Regarding XvMC, it is a very simple protocol. Surely ffmpeg could be
made to support it.
XvMC is still used by a lot of people to play SD content using older
STBs. Maybe the way forward is to make a VDPAU API to XvMC converter,
whereby software does a lot of the VDPAU API, and it uses XvMC where
it can. I think the difficulty might be in the fact that XvMC is MPEG2
specific, and cannot handle any MPEG4 media.

I agree that VDPAU (and similar) and OpenGL are the way forward for HD
content, but Xv and XvMC are still perfectly good for SD content.
For example, I have a small TV in the Kitchen. There is no sensible
reason for me to purchase a HD capable STB when the TV is only 17
inches and has no HDMI connector.

But, I then have a problem, keep the STB mythfrontend in the kitchen
at 0.24, and have .26 in the Lounge, but .26 might upgrade the backend
database, making it incompatible with 0.24 mythfrontend in the

I would also like to point out that although HDMI has been around for
a long time, I only got my first HDMI capable PC last week.
I do not think I am alone in this. Many other people will not be ready
to upgrade their hardware.

Kind Regards


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