[FFmpeg-devel] [PATCH 2/3] lavc: add a framework to fix alignment problems.

[Marton Balint]

On Sat, 6 May 2017, Ronald S. Bultje wrote:

> Hi,
>
> On Sat, May 6, 2017 at 5:20 AM, Nicolas George <george at nsup.org> wrote:
>
>> +    /**
>> +     * Minimum alignment of frame data required by the codec.
>> +     * All frame data pointers must have the alignment lower bits cleared,
>> +     * i.e. be a multiple of 1<<alignment.
>> +     * - encoding: set by the encoder and used by the framework
>> +     * - decoding: unused
>> +     */
>> +    unsigned alignment;
>> +
>>  } AVCodecContext;
>
>
> I agree it's likely that one codec (e.g. h264) would need 32-byte alignment
> on a particular system (e.g. x86/haswell), whereas another codec on the
> same system (e.g. wmavoice) might not.
>
> However, I find it unlikely that one codec *instance* would need different
> alignment from another codec *instance* (for the same codec).

I can imagine a case where alignment requirements are dependant on pixel 
format. Not the best example, because it is not a "codec", and it is using 
bitpacked formats, but the Decklink output device would require 128 byte 
or even 256 byte alignment for 10/12 bit, according to the SDK.

Regards,
Marton