[Nouveau] Video Hardware Decoding: Jittery Rectangles on Nvidia GT218 NVA8 VP4.

[Ilia Mirkin]

On Sat, Jul 27, 2019 at 7:37 AM Ralph Corderoy <ralph at inputplus.co.uk> wrote:
> The video plays, CPU load is less (my aim), but there's ‘tearing’ of the
> picture as if small rectangles that are updates are appearing in the
> wrong location, off by a little.  If I step through the frames with
> mpv's ‘.’ and ‘,’ then I've found a pattern: one frame's picture is
> good, followed by N bad ones where N is 3 or 7, i.e. every 4th or 8th
> frame is okay.  Don't know if that's a clue or helps someone here
> recognise a known problem.
>
> I know X well, but Mesa, etc., below it are unknown to me, even to the
> extent of knowing quite how all the bits fit together.  I'd appreciate a
> pointer or two as to how to tackle the problem, even if it's a ‘You've
> come to the wrong place, go over there’.  :-)

Unfortunately I've never tracked down the cause for this.
https://nouveau.freedesktop.org/wiki/VideoAcceleration/ - see note #4.

I have, over time, collected some sample videos where this happens in
the first few frames. The plan was to do mmt traces of the blob
driver, and figure out what it was doing differently. If this is
something you're interested in, I'd be happy to provide some guidance.
However my past efforts to work this out were fruitless. Hopefully
it's just something dumb we're doing in reference frame management, or
a missing bit in the info structures, or something else entirely since
I've scoured quite heavily for those two.

If you'd like to dedicate some of your time to working this out, you
can join us at #nouveau on freenode.

Cheers,

  -ilia