On 06.11.2015 20:28, Ilia Mirkin wrote:
On Fri, Nov 6, 2015 at 2:15 PM, Christian König <deathsim...@vodafone.de> wrote:
On 06.11.2015 20:10, Ilia Mirkin wrote:
On Fri, Nov 6, 2015 at 1:48 PM, Zhang, Boyuan <boyuan.zh...@amd.com>
wrote:
Hi Emil,
Please see the following information about this patch.
- Issue: For Mpeg4, the VOP and GOV headers were truncated. With the
existing workaround in st/va, playback shows massive corruptions.
- This Patch: Provide another way to get the truncated headers back.
Massive corruptions are gone with this patch. At the same time, add an
environmental variable to allow user to decide whether to use this patch.
Why would the user not want to use this? Sounds like a correctness
fix, no? Or is it some thing that a hypothetical gallium driver might
not need but the radeon uvd-based ones do? In that case it should be
behind a PIPE_VIDEO_CAP_bla (sorry, I'm still not too clear on what
"bla" is here...)
The problem is that this is a rather extreme hack.
As you probably knew VA-API didn't correctly specify which start code should
be included and which shouldn't for MPEG-4. This is an issue for AMD as well
as NVidia hardware and pretty much everybody which sticks close to an
elementary stream.
What we do in this hack is just searching the bytes *before* the pointer and
size we got from the application for the stuff that's missing. E.g. we
access memory the application didn't told us to access.
This is rather speculative, but works surprisingly well with a lot of
applications.
Hm, that is a little dodgy indeed. But making user-selectable options
(provided via env var) for correct decoding... doesn't seem ideal
either. Is there some "correct" way to resolve this without changing
the va api?
Unfortunately no. I wasn't involved in everything but we had a couple of
people working on this which have more knowledge about MPEG-4 part 2
than me.
A couple of month back somebody from a different team at AMD even tried
to convince Intel to fix this, but as far as I know without success.
The over all conclusion is that the interface definition of VA-API for
MPEG-4 part 2 is just a bloody mess.
Regards,
Christian.
-ilia
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