[FFmpeg-devel] [PATCH]Implement max_lowres

[compn]

On Wed, 7 Jul 2010 15:11:58 +0200, Michael Niedermayer wrote:
>On Wed, Jul 07, 2010 at 03:56:22PM +0300, Ivan Kalvachev wrote:
>> On 7/6/10, Michael Niedermayer <michaelni at gmx.at> wrote:
>> > On Tue, Jul 06, 2010 at 12:01:26AM +0200, Carl Eugen Hoyos wrote:
>> >> Hi!
>> >>
>> >> On Monday 05 July 2010 04:40:59 pm Michael Niedermayer wrote:
>> >>
>> >> > > First version attached. Is there an API-change or Changelog entry
>> >> > > needed?
>> >> > > Note that this should not be held back because of the obvious
>> >> > > regressions: ffmpeg -lowres is currently broken for default configure
>> >> > > anyway;-)
>> >>
>> >> > i dont think mpeg1/2 are the only that support lowres
>> >>
>> >> As I said, this should currently be no reason to delay this patch.
>> >
>> > i disagre
>> > only codecs that are confirmed to fail / not support it should be limited
>> > not limit by default and loose feature in all untested codecs
>> 
>> I don't like the whole lowres thing.
>> Long time ago a friend wanted to use cheap Pentium166 laptop to play
>> some mpeg4 videos.
>> 
>> In my tests lowres=3 (that is resolution decreases by 8x8, or 1 pixel
>> per mpeg1/2/4 block) gives just 30% speedup (that is, 70% of the
>> normal full resolution playback). The same amount of speedup is much
>> easier achieved by gray only decoding (skip color planes), that also
>> gives image of much higher quality - full resolution and no
>> accumulation of decoding artifacts.
>> 
>> Indeed lowres was clever idea and intriguing experiment, but I
>> consider that it is practically useless.
>> 
>> So I would like to ask, would you consider removing lowres altogether?
>
>you want a feature to be removed?
>anyway, the amount of speedup depends on the file and where the bottleneck
>is. With very very high bitrate videos the gain from lowres is small
>also as long as we only support sdl, its absolutely needed as workaround
>for ffplay to be useable because sdl fails randomly above some resolution with
>some hardware
>
>besides i wouldnt expect much meassureable gain for the normal case by
>removing it.
>
>that said, i wont approve lowres being removed, make it compile time optional
>if you like but its usefull for other people, i am one of these people btw.

i like lowres, i havent used it in a while tho. if gray is so much
better you might want to put it in the docs or faq so people know to
use that instead.

-compn