[FFmpeg-devel] [PATCH] avdevice/v4l2: add limited support for multiplanar API

[Ramiro Polla]

On Tue, Jun 25, 2024 at 1:56 PM Ramiro Polla <ramiro.polla at gmail.com> wrote:
> On Tue, Jun 25, 2024 at 11:19 AM Anton Khirnov <anton at khirnov.net> wrote:
> > Quoting Ramiro Polla (2024-06-20 17:40:39)
> > > This commit adds support for V4L2's multiplanar API, but only when the
> > > number of planes is 1.
> > >
> > > Adding full support for the multiplanar API would require a device that
> > > actually uses more than 1 plane, which I have not found yet.
> >
> > Out of curiosity, what's the point of a multiplanar API when the plane
> > count is always one?
>
> Good question, and I wish I knew the answer. Some SBCs are providing
> HDMI input through v4l2, and they decided to use the multiplanar API,
> even though the count is always one.
>
> I couldn't find many examples on how to use this API correctly, with a
> couple of implementations being buggy to a point where they will only
> work when the count is one.
>
> I wish I could find a device that uses the multiplanar API and
> actually provides more than one buffer so that I could properly test,
> but by looking at the kernel source code I couldn't find a device that
> I could easily obtain yet.

Is anyone fundamentally opposed to this approach to implement limited
support for multiplanar API? I figure it could still be useful even
when full multiplanar API support is implemented, because multiple
memory buffers per packet will likely mean memcpy()s, which can be
avoided if the plane count is one.