David,

I guess I don't quite understand what it is you are trying to do. In 
general, you cannot play audio faster without dropping any frames unless 
you change the pitch. So something's gotta give -- total number of samples 
or pitch.

If it is OK to change pitch, try opening the audio device at a higher rate 
than advertised, i.e. open it at 44, but make the core believe that it was 
opened at 22. In that case, the core will resample the audio to 22 kHz, but 
it will be played back at 44 (thus shifting the pitch by an octave), and 
twice as fast.

(Now, if this actually will work as expected, I don't know -- for example, 
you have just doubled the bitrate without letting the core know. It might 
work for local playback, but probably not streaming).

- Wolfgang

At 01:32 PM 5/13/2003 -0400, wg - drs wrote:
>Hi Eric,
>
>
>I've tried playing a littlle bit with faster than real time playback but
>haven't had any success.  Can you or someone explain how the mechanism works
>in greater detail?
>
>I tried dividing my granularity by  a speed factor and scheduling my
>callback to my audio device based on that ms time value (99ms went to 71 ms)
>but that didn't appear to have any change on the play back speed.
>
>David
>
>----- Original Message -----
>From: "Eric Hyche" <ehyche at real.com>
>To: "wg - drs" <drs at duneram.com>; <dev at helix-client.helixcommunity.org>
>Sent: Tuesday, May 06, 2003 11:01 AM
>Subject: Re: [hxclidev] client sdk -- speeding up playback
>
>
> >
> > At a high level, the way folks have done this in the past is
> > to replace the audio device classes with their own. Since the
> > timing of the media engine is driven from the audio device,
> > then if you have your own audio device you control the clock.
> > I think a company called Enounce (http://www.enounce.com/)
> > sells a product that does this. However, from helping them
> > with issues in the past, I remember this being a very involved
> > task.
> >
> > I don't know of a turnkey way to play a file backwards
> > using the SDK.
> >
> > Eric
> >
> > At 10:37 AM 5/6/2003 -0400, wg - drs wrote:
> > >Hi,
> > >
> > >Is there a way in the client sdk to speed up the playback of a media
> > >'file'  and not drop any video or audio frames?
> > >
> > >I'd like to be able to playback at 2x or higher.
> > >
> > >Also not as pressing but still have interest, is there a way to play a
> > >file backwards through the SDK?
> > >
> > >Thanks
> > >
> > >David
> >
> >
> >
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> >
>
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-
- Wolfgang Schildbach, Principal Codec Engineer, RealNetworks Codec Group
- email wschildbach at helixcommunity.org



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