[Theora-dev] Re: PC-based video server

Timothy B. Terriberry tterribe at vt.edu
Wed Jan 26 21:43:29 PST 2005

> So what do you think with the above said - no loop filtering. Will it
> really be faster?

Hmm, yeah, if you keep quality high enough to avoid loop filtering, then 
drift artifacts should be eliminated. So that'll give you more memory 
bandwidth savings and fewer multiplies in the IDCT (Theora already uses 
a simpler IDCT implementation when all the non-zero coefficients are in 
the first 10 zig-zag positions, so this is relatively easy to adapt the 
software to).

> What I need for this project is not direct Theora -> MJPEG, but
> Theora->MJPEG with "digital PTZ" (zoom - probably just 1/2/4/8). And that
> PTZ over full-resolution Theora data will be needed even without
> transcoding - we already ran into similar problem working with multiple

I had been interpreting your use of PTZ to mean decoding a small, 
rectangular region of the full frame at a possibly reduced resolution. 
If you mean simulating a _real_ PTZ camera, as in recovering depth from 
multiple views and actually re-projecting the geometry, this is another 
problem altogether.

But mostly what I was talking about with transcoding is operating 
directly on the DCT coefficients, without ever going back to the spatial 
domain. Obviously, to me at least, this is no different whether your 
doing this over a small ROI or over the full frame, aside from the 
number of blocks you need to operate on. My familiarity with the 
internal workings of JPEG, however, is much smaller than those of Theora 
(since I haven't written a JPEG encoder/decoder, nor written its 
specification... or actually even read its specification), but in theory 
it seems like it'd be doable.

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