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

[Paul B Mahol <onemda@gmail.com>]

On 10/2/23, Anton Khirnov <anton@khirnov.net> wrote:
> 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.

But that would break SDR seeking.
And also break bunch of avdevice, and make Nicolas sad.

>
> --
> Anton Khirnov
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