From: James Courtier-Dutton <J<ames@su...> - 2001-08-28 21:39:06
I wanted to start a discussion on how reverse play might be achieved with
There are three types of pictures that use different coding methods:
1) an Intra-coded (I) picture is coded using information only from itself;
2) a Predictive-coded (P) picture is a picture which is coded using motion
compensated prediction from a
past reference frame or past reference field;
3) a Bidirectionally predictive-coded (B) picture is a picture which is
coded using motion compensated
prediction from a past and/or future reference frame(s).
So, it seems to me that we could put the as yet not decoded frames in an
This order would be in the order in which they would be displayed if playing
I am assuming here that a single frame (I, P, or B) maps to an actual frame
to be displayed on the screen.
This ordered list would then label each frame, 1,2,3 etc.
The xine engine would then request a frame number, and the mpeg2 decoder
would only then do the decoding, and display the frame.
So, for normal play, the xine engine would request frame 1, then 2, then 3
For reverse play, the xine engine would request from 3, then 2, then 1 etc.
For double speed, the xine engine would request 1, then 3, then 5 etc.
For faster speed, the xine engine would request 1, then 4, then 7 etc.
Is there something in the current mpeg2 decoder which would make this too
I know reverse play should be possible, because DVD players can do it.
Nothing in this world is exactly what it appears to be.
On Tue, 28 Aug 2001, James Courtier-Dutton wrote:
> I wanted to start a discussion on how reverse play might be
> achieved with xine.
who needs reverse playback?
> So, it seems to me that we could put the as yet not decoded frames in an
> ordered list.
> This order would be in the order in which they would be displayed if playing
you really want to build an index of the complete stream? A complete 2h
movie is 180000 frames and you'd have to seek through approx. 5 GB of
mpeg2-data to compute that list (which is only possible for seekable
> The xine engine would then request a frame number, and the mpeg2 decoder
> would only then do the decoding, and display the frame.
hum, the question is _how_ the mpeg2 decoder could decode an arbitrary
selected frame - reverse motion compensation or something like that?
time is a funny concept
Sorry, didn't have time to cover up lately...
> > I wanted to start a discussion on how reverse play might be
> > achieved with xine.
> who needs reverse playback?
I need it occassionally. And I would like to have it as well :^)
Just for you, Guenther, to see that there actually are people out there
that would love that one. And won't know exactly, how to implement it either
Matthias Hopf - Visualization and Interactive Systems Group \ | | /--
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