Kenneth Arnold (ken@arnoldnet.net) wrote :> On Mon, Oct 09, 2000 at 02:46:57PM -0700, Ralph Giles wrote:
> > Re minimal facilities, all the compressed stream can really do is
provide
> > timestamps (or ranges). It's easy enough to keep track of exactly
where
> > you are in the decoder (libvorbis provides sample-accurate seeking,
for
> > example).
What about sub-sample-accurate seeking ? ( that is not really seeking
any more, is it ? )
In certain surround sound setups the timings are very important
and only one-sample steps may not be enough.
> > In the trivial implementation, it's just a matter of lining up
> > the numbers.
>
> Right... more pains in decoders' butts. Ah well, I guess we're
going to
> have to live with it. It's not like there's much better, other than
> SMTPE-timecoding the whole system (which I think should be done possibly
> as metadata, because it's possible that the video should interface with
> systems that use SMTPE (e.g., broadcast).
>
> > A more sophisticated approach is to write some sort of scheduler that
> > works to (1) keep the audio buffer full (2) display video and text
frames
> > at the appropriate time (3) issue packets to the various decoders so
the
> > above can happen as smoothly as possible given available system
resources.
>
> True: some smarts there can get the same result.
>
> > Some suggested heuristics:
> >
> > maintaining audio is the most important thing. drop video frames as
> > necessary down to 1-per-5-seconds or so. then drop audio.
>
> But what about inter-frame coding? Wouldn't this totally mess up the 3d
> wavelets?
Is this about "keep audio and video ( and others ) in sync" or
"what to do if the CPU can't decode in real time" ?
Why would this mess up the wavelets ? The wavelet decoder spits out
the frames which are displayed or maybe not displayed. It is of no
concern
of the decoder engine.
> > Text (closed captions/subtitles) is better run 'fast-forward'
or displayed
> > in aggregate than dropped.
> yes.
>
Same for video. Speeding up and slowing down video is trivial, unless
you are running in sync with the hardware framerate ( which you aren't
on any display over 70 Hz of vertical sync ).
If you're outputting to a TV then you may have problems , but there
are solutions ( PAL on NTSC VCR's and DVD players use them for example )
--
David Balazic
--------------
"Be excellent to each other." - Bill & Ted
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