[FFmpeg-devel] [PATCH] ac3enc: add num_rematrixing_bands to AC3EncodeContext and use it instead of the hardcoded value.

[Justin Ruggles]

On 03/05/2011 06:24 AM, Reimar D?ffinger wrote:

> On Fri, Mar 04, 2011 at 04:47:14PM -0500, Justin Ruggles wrote:
>>
>> Currently it is always 4, but this change will allow it to be adjusted when
>> bandwidth-related features are added such as channel coupling, enhanced
>> channel coupling, and spectral extension.
> 
> Did you benchmark? If the compiler could do loop unrolling before it
> might be significant.

I can benchmark it, but it will have to be changed eventually anyway.

>> @@ -1304,7 +1307,7 @@ static void output_audio_block(AC3EncodeContext *s, int blk)
>>          put_bits(&s->pb, 1, block->new_rematrixing_strategy);
>>          if (block->new_rematrixing_strategy) {
>>              /* rematrixing flags */
>> -            for (rbnd = 0; rbnd < 4; rbnd++)
>> +            for (rbnd = 0; rbnd < s->num_rematrixing_bands; rbnd++)
>>                  put_bits(&s->pb, 1, block->rematrixing_flags[rbnd]);
> 
> Also it seems a bad idea to me to replace the constant 4 in the loop
> bounds while not doing so in the rematrixing_flags declaration.
> E.g. an assert that s->num_rematrixing_bands is not larger than
> the rematrixing_flags size might make sense to add somewhere.


It never will be greater than 4.  An assert() could certainly be added
later, but even when it's calculated during each frame encode it will be
a simple equation that is obviously always between 0 and 4.

-Justin