[FFmpeg-devel] [RFC] avcodec: Add native DCA decoder based on libdcadec.

[Andreas Cadhalpun]

On 06.01.2016 18:32, foo86 wrote:
> On Tue, Jan 05, 2016 at 10:46:19PM +0100, Andreas Cadhalpun wrote:
>> OK. This decoder seems to be quite robust in handling fuzzed samples,
>> so from a security point of view it should be fine to replace the
>> old dca decoder with this one.
> 
> Out of interest, did you disable CRC checks in the decoder while fuzzing?

No, I tested it as is.

> Otherwise testing coverage will be decreased somewhat. The easiest way to do
> this is to modify ff_dca2_check_crc() to always return 0.

I tried this (comment out everything in ff_dca2_check_crc except 'return 0')
and there doesn't seem to be much difference.

>> Out of curiosity: Can you post a few benchmarks comparing the performance
>> of the old and the new decoder?
> 
> Here are some benchmarks I did with 3 available decoders on 3 different
> systems: (1) x86_64 desktop, (2) ancient i386 laptop, (3) Raspberry Pi Model
> B+.
> 
> Measuring how much time it takes to loop 2000 times over a short 5.1
> channel core sample (for a total duration of 00:51:56.22) yields the
> following results:
> 
>             dca         dca2        libdcadec
> System 1:   0:11.90     0:11.16     0:19.73
> System 2:   0:57.00     0:55.23     1:21.33
> System 3:   7:41.31     7:00.84     13:16.70
> 
> The new decoder appears slightly faster than dca even though it doesn't
> use any assembly optimized code for dcadsp (besides synth_filter).

Thanks for sharing these benchmarks. They look quite nice. ;-)

Best regards,
Andreas