[mythtv] Seg Fault in mediacodec

[David Engel]

On Thu, Jul 05, 2018 at 12:48:52PM -0400, Peter Bennett wrote:
> On 07/05/2018 12:34 PM, David Engel wrote:
> > On Wed, Jul 04, 2018 at 02:51:31PM -0400, Peter Bennett wrote:
> > > On 07/04/2018 11:27 AM, Aman Gupta wrote:
> > > > You can also try setting the ffmpeg loglevel to trace which will show
> > > > much more detailed info about each output buffer being returned from the
> > > > decoder. A segv in memcpy is pretty low level so it's unclear if this is
> > > > something we would be able to fix in ffmpeg ourselves.
> > > > 
> > > The output is attached. From it we can see that 18 packets were sent in,
> > > then 8 frames were retrieved and it seg faulted on retrieving the ninth. In
> > > the code it is trying to memcpy the frame from the buffer returned by
> > > mediacodec to the buffer allocated by ffmpeg when it hits the seg fault.
> > On the unlikely chance the problem is specific to copying decorded
> > frames from graphics memory, I disabled the Surface support in Kodi so
> > it uses OpenGL for rendering like we currently do.  It still worked
> > which reinforces the problem is with us or ffmpeg.
> > 
> > David
> I reduced the number of buffers so that it displays a couple of frames
> before crashing. I see a fat green line along the bottom. I suspect that it
> is trying to use a frame size of 1920x1088 instead of 1920x1080 (see the
> trace I sent, it shows slice-height 1088). I plan to step through the ffmpeg
> code and see if perhaps it is copying 8 rows more than it should. I don't
> know what the slice-height refers to, but it looks suspicious.
> 
> It may be that the problem is associated with 1080 rows. Of the resolutions
> I have tried, only 1080 is not divisible by 16. I have tried 480, 720, 2160
> - all work without seg fault.

You could be on to something.  The a/v side of things is not an area
with which I'm intimately familier, however, I vaguely recall various
issues with 1080 vs. 1088 popping up in the past.  Where's Mike Dean
when we need him? :)

David
-- 
David Engel
david at istwok.net