[FFmpeg-devel] MPEG-2 FLAGS2_FAST benchmarks

[Kieran Kunhya]

>
> > Also the speed benefits are tiny overall, sub-1%.
>
> This claim is not supported by the statistics you posted
>

For the overall decoding of MPEG-2 the VLC/dequant functions take up
roughly 30% of decoding time.
FAST vs normal is about 2% faster on the VLC/dequant functions, therefore
the total speed benefit of FAST is sub-1% for MPEG-2.


> > Removing it and some
> > other small changes to the existing code will make the existing code run
> at
> > the same speed.
>
> its a long time since we had mpeg1/2 optimizations
> iam very happy about this being speed up more.
> If you manage to make it as fast as fast mode i surely would be happy
> If you manage to make the difference shrink by half i too would be happy.
> Faster decoding of mainstream codecs is a good thing. It has many
> advantages ...
>

Part of the speed difference is the if(FLAGS2 & FAST) branch being gone on
each macroblock.
However, if you are not willing to remove FAST I don't see the point of
continuing.
You have free reign to "optimise" FAST to justify its existence as it
doesn't have to conform to any spec.

Kieran