[MPlayer-users] how to "step backforward" ?

[belcampo]

Oliver Seitz wrote:
>> My feeling is that the full frame caching is certainly more general and
>> probably easier to implement, and would mean consistent behaviour
>> regardless of source. People will scream about the massive memory
>> footprint, but it seems like a reasonable application of RAM to me.
> 
> I've thought about that, but the method lacks of inflexibility. You then
> can only step back to frames you've recently played. I think if there is a
> feature for stepping back one frame it should do that, regardless if the
> part was played before. If the cache of decoded frames has to be extended
> backwards you get almost the behavior of VirtualDub, just a bit more
> complex and memory consuming.
> 
> I am quite unfamiliar with video file formats. Is it true that frames are
> accessed via some sort of "linked list" and is therefore difficult to find
> the start of a certain frame? Implementing a cache storing the entry
> points of every frame may help. If not the file position but the length of
> each frame is stored, 32bit should suffice. 1MB of cache would hold enough
> frame lengths for 2.5 hours of video. This "extended index" could be
> generated on request by command line switch.
> 
> Sorry, I'm dreaming ;-)
AAASSSS FFFFAAAAAARRRRRR AAAAAASSSSS  IIIIIII KKKKKNNNNNOOOOOOWWWWWW !!!

I-Frames/Key-Frames are 'a whole picture' following frames are more or 
less 'former-frame plus/minus the difference'.
following frames are calculated from those origin and differences. So 
stepping forward is rather simple, it is 'normal'play at non-standard speed.
Going back is difficult in the sense you have to calculate several 
frames plus/minus the differences to 'know' how that former frame has 
looked.
> 
> Greets,
> Kiste
> 
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