[FFmpeg-devel] [PATCH] avcodec.h: document padding requirements for get_buffer() callback.

[James Almer]

On 1/2/2025 7:39 PM, Ronald S. Bultje wrote:
> ---
>   libavcodec/avcodec.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
> index 12e6e8749f..7ecb819dae 100644
> --- a/libavcodec/avcodec.h
> +++ b/libavcodec/avcodec.h
> @@ -1199,7 +1199,8 @@ typedef struct AVCodecContext {
>        * some other means.
>        *
>        * Each data plane must be aligned to the maximum required by the target
> -     * CPU.
> +     * CPU. In addition, each data plane must be padded by that same amount
> +     * plus 15 bytes.

IMO, remove the 15 bytes part. Even if the default allocator adds those, 
asking for max_cpu_align padding bytes should be more than enough.

And for that matter, see fuzz_video_get_buffer() in 
tools/target_dec_fuzzer.c, where no such thing is done precisely to 
simulate what a user reading this doxy might do with their own custom 
callback. This padding should in theory not be a requirement when 
avcodec_align_dimensions2() is documented as handling this stuff.

Maybe avcodec_align_dimensions2() should be updated for VP9 to 
overallocate? I see it does for h264, vp6 and many other codecs where 
the native decoder overreads for different reasons.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: OpenPGP_signature.asc
Type: application/pgp-signature
Size: 495 bytes
Desc: OpenPGP digital signature
URL: <https://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20250102/82f24fda/attachment.sig>