Re: [FFmpeg-devel] [PATCH] avdevice/v4l2: Switch to wrapped AVFrames and implement strides

[Anton Khirnov <anton@khirnov.net>]

Quoting Asahi Lina via ffmpeg-devel (2023-09-29 09:52:23)
> V4L2 provides a line stride to the client for hardware that has
> alignment requirements. rawvideo cannot represent this, so switch to
> wrapped_avframe for raw video formats and calculate the plane strides
> manually.
> 
> This is slightly messy because the existing helper APIs expect
> dimensions and an alignment value, while v4l2 provides the stride of
> plane 0 and the subsequent plane strides are implied, so we need to
> open-code the logic to calculate the plane strides.
> 
> This makes vertical video work properly on Apple Macs with "1080p"
> cameras, which are actually square and can support resolutions like
> 1080x1920, which require stride padding to a multiple of 64 bytes.
> 
> In principle, this could be extended to support the V4L2 multiplanar
> API, though there seem to be practically no capture (not M2M) drivers
> that support this, so it's not terribly useful right now.
> 
> Signed-off-by: Asahi Lina <lina@asahilina.net>
> ---
>  libavdevice/v4l2-common.c |  68 +++++++++++------------
>  libavdevice/v4l2.c        | 138 +++++++++++++++++++++++++++++++++++++++-------
>  2 files changed, 151 insertions(+), 55 deletions(-)

Wrapped AVFrames is an abominable hack that should be going away, not
spread to new places. The correct approach is move v4l2 rawvideo to a
lavfi source filter, then none of these hacks are needed.

-- 
Anton Khirnov
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