[mythtv] FFmpeg mediacodec problem

[David Engel]

On Thu, Jun 14, 2018 at 03:42:14PM -0400, Peter Bennett wrote:
> 
> 
> On 06/14/2018 03:04 PM, Aman Gupta wrote:
> > 
> > 
> > On Thu, Jun 14, 2018 at 11:59 AM Peter Bennett <pb.mythtv at gmail.com
> > <mailto:pb.mythtv at gmail.com>> wrote:
> > 
> >     Hi Aman
> > 
> >     mediacodec playback is working quite well now in mythfrontend, but I
> >     have a problem with ffmpeg as follows:
> > 
> >     When decoding 3840x2160 content, there is pixellation caused by
> >     dropped
> >     frames. The frames are being dropped because of apparent inconsistent
> >     behavior in ffmpeg.
> > 
> >     MythTV calls avcodec_send_packet to send the next packet. It receives
> >     -11 return code (EAGAIN) indicating it must call
> >     avcodec_receive_frame
> >     and then try to send again. We call avcodec_receive_frame and it
> >     is also
> >     getting a -11 return code indicating it must send a packet before
> >     it can
> >     receive. According to the documentation this will never happen.
> >     MythTV
> >     then reports an error, drops the packet and moves on to the next one.
> >     This is happening many times. eventually the avcodec_receive_frame
> >     works
> >     and we receive a frame, but later the pattern repeats.
> > 
> > 
> > This is a known issue, cause by an incompatibility between how
> > MediaCodec's APIs work vs how FFmpeg's abstraction works.
> > 
> > Ideally MediaCodec would provide a way for us to know whether it needs
> > to wait on input or output. But no reliable way to do this exists, so
> > the FFmpeg wrapper has to make a guess. And sometimes that guess is
> > wrong. I'm aware that we're breaking the API contract as defined by
> > libavcodec, but I haven't been able to find a solution.
> > 
> > The only workaround for now is to retry sending the original packet
> > instead of dropping it. The second time you call avcodec_send_packet it
> > should block instead of returning EAGAIN.
> > 
> > Aman
> > 
> > 
> >     I tried turning on ffmpeg debug logging but I did not see any message
> >     from that.
> > 
> >     Please advise what should be done. Let me know if you need more
> >     information.
> > 
> >     Peter
> > 
> 
> Hi Aman
> 
> Thanks for the info. I tried it and the second call to avcodec_send_packet
> does not block, it also returns -11.
> 
> So what I have done is, sleep 10 milliseconds, then try the receive and the
> send again. Continue like this until it works. Now the video is perfect :).
> 
> FYI - what I see is - at the start of playback:
> 10 packets sent
> 9 fails and retries to send next packet (above condition)
> 4 packets sent
> 1 frame received
> 
> After this it sends and receives ok, with one fail and retry every 10 frames
> or so.

Whateve you wind up with, you probably want to add some overall
timeout.  For example, if returns EAGAIN for 10 seconds, it's probably
time to give up.

> So I think I have a working solution.

I'm looking forward to trying this this weekend. :)

David

> Thank you.
> 
> Peter
> 

-- 
David Engel
david at istwok.net