[x264-devel] The size of search area in reference frames

[Radek Czyz]

On 14/06/2010 3:48 PM, john sisi wrote:
> Thanks for the reply. Since moving objects can move further over a
> larger interval of time, so a larger search area must be used for
> motion estimation. The larger the search area, the higher the
> computational complexity.

Yes, but only in case of full search.
Any sane motion search algorithm doesn't have a concept of "search area" 
at all. It can only have a maximum vector size allowed but increasing 
this value has no effect on complexity (for values large enough).

 > But as you mentioned, x264 always uses a fixed window size (or maximum
 > search range or vector size) on all reference frames which I think is
 > not an efficient strategy. But am I right?

Full search could be the definition of inefficiency :) so of course. But 
nobody uses it so it doesn't matter.

Regards


  In other words, assuming that the size of
> the search window (for either fullpel or quarterpel motion estimation)
> in the first reference frame is 32x32, this size in the second
> reference frame must be about 64x64 (assuming that objects has a
> linear speed) and so on.
>
> But as you mentioned, x264 always uses a fixed window size (or maximum
> search range or vector size) on all reference frames which I think is
> not an efficient strategy. But am I right?
>
> John
>
> On Sun, Jun 13, 2010 at 11:15 PM, Jason Garrett-Glaser
> <darkshikari at gmail.com>  wrote:
>> On Sun, Jun 13, 2010 at 10:54 PM, Radek Czyz<radoslaw at syskin.cjb.net>  wrote:
>>> On 14/06/2010 2:45 PM, john sisi wrote:
>>>>
>>>> Hi All,
>>>>
>>>> As you may know better, due to the movement of objects, the search
>>>> area for motion estimation in reference frames must be increased in
>>>> order to achieve better PSNR performance. But it seems that x264
>>>> doesn't increase the size of the search area in the reference frames
>>>> and it always uses the same size. But am I right? If not, please
>>>> correct me by showing where this issue is handled. Thanks,
>>>>
>>>> John
>>>
>>> Hi,
>>>
>>> Since you're asking for details of x264, can you describe your question more
>>> in terms of x264's workings?
>>>
>>> Particularly, what is this "search area" (do you mean during fullsearch
>>> only?) and from what it should be increased (that is, why was "it" decreased
>>> in the first place).
>>>
>>> x264 has maximum vector size as part of its configuration but, as its name
>>> suggests, it's already a maximum allowed, and it's up to the user to
>>> increase it if he wants to allow more.
>>
>> x264 by default uses the maximum allowed by the spec (for maximum
>> vector size).  The user can't ask for more.
>>
>> Dark Shikari
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