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

From: Ming Qian <ming.qian@nxp.com>
To: Andriy Gelman <andriy.gelman@gmail.com>
Cc: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [EXT] Re: [PATCH v4 2/3] avcodec/v4l2_context: resume the decoding process after source change event received.
Date: Wed, 5 Jan 2022 02:02:02 +0000
Message-ID: <AM6PR04MB63411F3C3CF3FB9464135535E74B9@AM6PR04MB6341.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <20220104225802.btiwwikprkeaqf2e@jackie>

> -----Original Message-----
> From: Andriy Gelman [mailto:andriy.gelman@gmail.com]
> Sent: Wednesday, January 5, 2022 6:58 AM
> To: Ming Qian <ming.qian@nxp.com>
> Cc: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
> Subject: Re: [EXT] Re: [FFmpeg-devel] [PATCH v4 2/3] avcodec/v4l2_context:
> resume the decoding process after source change event received.
> 
> Caution: EXT Email
> 
> On Tue, 04. Jan 17:48, Andriy Gelman wrote:
> > 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%2F
> > > > streams
> > > > .videolan.org%2Fffmpeg%2Fincoming%2F720p60.mp4&amp;data=04%7
> C01%
> > > >
> 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.
> 
> Also you may have to upgrade kernel to reproduce. It may have been working
> fine before this commit:
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.
> com%2Fraspberrypi%2Flinux%2Fcommit%2Fb7e6b495eff31298ba4665f71b2
> 414cc9a8f99c2%23diff-93defb6da917ce9bb43cb195d0e61f81673c5183ac75
> d631f3e1ee475a810dd6&amp;data=04%7C01%7Cming.qian%40nxp.com%7C
> 64fa84ae1325497b2b4408d9cfd5aabd%7C686ea1d3bc2b4c6fa92cd99c5c301
> 635%7C0%7C1%7C637769338865335050%7CUnknown%7CTWFpbGZsb3d8e
> yJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%
> 7C3000&amp;sdata=ZCuu2FL5EusXxilM%2BkdpLjQDXnvVhFIXsKeIVHPKWHY%
> 3D&amp;reserved=0
> 

I got it, but I didn't have a Raspberry Pi4 on hand right now, maybe I can test it again after I get one.
I make this patch according the v4l2 decoder specification and test it on NXP i.MX 8Q and i.MX8M

> --
> Andriy
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