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

[Lynne]

On 03/01/2025 07:47, James Almer wrote:
> 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.

Yeah, avcodec_align_dimensions2() should be used to control padding. 
Users are supposed to call it.
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