Re: [Mlt-devel] Compiler options/optimisation

[Paul F. <pa...@fl...>]

Actually, ignore this - I can see it *should* be there but for some 
reason it's disappeared locally

On 04/02/11 17:16, Paul Flinders wrote:
> Unless I've missed something the build scripts and Makefiles do not 
> enable compiler optimisation when building MLT.
>
> For the most part this probably isn't going to impact on performance 
> all that much - a lot of MLT is glue code which is using other 
> libraries to do the work.
>
> However MLT does do some video processing of its own - notably 
> dissolves and composites. For this code enabling optimisation does 
> make a significant impact. For example dissolve_yuv runs about 3x 
> faster when compiled with -O3 (though it would benefit massively from 
> an SIMD implementation).
>
> The impact in overall rendering time isn't huge - in a rather 
> contrived example of two 30 second AVCHD clips slowly (30 secs) 
> dissolving from one to the other the rendering time fell from 1:14 to 
> 1:07 (output using H.264 lossless_fast), just a 7 second improvement. 
> Whilst this is just under 10% for this example I suspect a lot of 
> productions don't accumulate 30 seconds of time dissolving one clip to 
> another.
>
> Having said that one area where I think it does make a difference is 
> when using editing software. I'm tending to use Kdenlive at present 
> and while AVHCD clips play fine in the project monitor as soon as you 
> hit a dissolve things start to stutter badly - enabling optimisation 
> doesn't quite make things pay smoothly but it does improve things 
> quite a lot (on a 4GHZ core i7 - YMMV).
>
> The attached patch adds -O3 to the default compiler options and 
> provides a switch to disable optimisation if required.