[MEncoder-users] Adding harddup as an afterthought?

[Loren Merritt]

On Thu, 27 Sep 2007, Rich Felker wrote:

> On Thu, Sep 27, 2007 at 05:42:28AM +0000, Ilya Zakharevich wrote:
>>> In principle you could drop-in zero-change frames, but the presence of
>>> B frames would make it a lot more complicated.
>>
>> Why?  I do not know the precise details of ASP, but why would the
>> following not work:
>>
>>   a) if the preceding frame is I or P, drop in a zero-change frame;
>
> I think the motion vectors in P frames might be predicted from the
> vectors of the previous frame, in which case this would break
> subsequent frames. But I'm not familiar with the details so I may be
> wrong about this.

P frames' motion vectors do not depend on other frames, so a zero-change 
P-frame would work.

>>   b) if the preceding frame is B, duplicate it?
>>
>> (Of course, it could overload the maximal count of B-frames supported
>> by the player; but I do not think the probability of this mattering is
>> high...)

I don't know of any players that have any limit on the number of B-frames
(except maybe Quicktime, which is broken in too many ways to count)

> This would probably work decently, albeit wasting some space.

B-frames' mvs are predicted from the following P-frame's mvs.
And the prediction formula depends on the relative frame numbers, so 
inserting a new B-frame would break any existing adjacent B-frames even 
if you got the new frame to work.

--Loren Merritt