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

[belcampo]

belcampo wrote:
> 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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> 
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In PAL-land we have I-frame/Key-frame every 12th frame. The max you need 
to enable back-stepping is the info of 12frames at DVD-quality that 
needs ((9000kb/25)*12)/8 about .54MB of memory. There will some more for 
overhead but you won't need that much "I think".
PS. I only have a small head with no so much brains in it.