Re: [FFmpeg-devel] [EXT] Re: [PATCH v4 2/3] avcodec/v4l2_context: resume the decoding process after source change event received.

[Andriy Gelman <andriy.gelman@gmail.com>]

Hi Ming,

On Tue, 04. Jan 07:51, Ming Qian wrote:
> 
> > -----Original Message-----
> > From: Andriy Gelman [mailto:andriy.gelman@gmail.com]
> > Sent: Monday, January 3, 2022 12:41 AM
> > To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
> > Cc: Ming Qian <ming.qian@nxp.com>
> > Subject: [EXT] Re: [FFmpeg-devel] [PATCH v4 2/3] avcodec/v4l2_context:
> > resume the decoding process after source change event received.
> > 
> > Caution: EXT Email
> > 
> > On Thu, 19. Aug 16:55, Ming Qian wrote:
> > > client need to resume the decoding process after it dequeues the
> > > source change event.
> > > no matter what's the return value of v4l2_resolution_changed().
> > > if the client doesn't resume the decoding process, the decoder may
> > > keep waiting
> > >
> > > in documentation of v4l2 stateful decoder, we can see the following
> > > description:
> > >       The client must continue the sequence as described below to
> > >       continue the decoding process.
> > >       1.  Dequeue the source change event.
> > >               Important
> > >               A source change triggers an implicit decoder drain,
> > >               similar to the explicit Drain sequence. The decoder is
> > >               stopped after it completes. The decoding process must be
> > >               resumed with either a pair of calls to
> > >               VIDIOC_STREAMOFF() and VIDIOC_STREAMON() on the
> > CAPTURE
> > >               queue, or a call to VIDIOC_DECODER_CMD() with the
> > >               V4L2_DEC_CMD_START command.
> > >       2.  Continue with the Capture Setup sequence.
> > 
> > Please also add that this fixes decoding of
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fstreams
> > .videolan.org%2Fffmpeg%2Fincoming%2F720p60.mp4&amp;data=04%7C01%
> > 7Cming.qian%40nxp.com%7Cea94a9c4cc0643b0a41f08d9ce0eadc5%7C686e
> > a1d3bc2b4c6fa92cd99c5c301635%7C0%7C1%7C637767384703207931%7CU
> > nknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6
> > Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=X4rKQX19MQg1gO3ILiBCQ
> > qSLIvqovZLA95KKiyoVNzI%3D&amp;reserved=0 on RPi4.
> > 

> 
> Hi Andriy,
>     What's wrong with this stream? Everything is normal on my side when I play it using ffplay.
> 

I couldn't decode the file on the Raspberry Pi4. After enqueuing the first few packets
there was a dynamic resolution change event, and the start decode command
was not sent. This is fixed by your patch.

Thanks,
-- 
Andriy
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