[mythtv] FFmpeg mediacodec problem

[Peter Bennett]

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.

So I think I have a working solution.
Thank you.

Peter

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