[Speex-dev] Decoding multiple encoded frames

[Darren Longhorn]

Keith Kyzivat wrote:
> Caveat: Take what I'm saying with a grain of salt -- I haven't actually
> written any code that decodes speex frames myself, though I have written
> code using Jean-Marc's Speexdsp lib.
> 
> Comments below inline
> 
> On Thu, Oct 9, 2008 at 9:28 AM, Darren Longhorn
> <darren.longhorn at redembedded.com
> <mailto:darren.longhorn at redembedded.com>> wrote:
> 
>     I think I still didn't fully understand. As a test I encoded some frames
>     (wideband, with quality set to 8), each were 70 bytes. I then did three
>     things:
> 
>      - passed half of it to the decoder
>      - passed exactly one frame to the decoder
>      - I passed two concatenated frames to the decoder.
> 
>     In all cases speex_decode_int returned 0.
> 
>     Unless I misunderstood what you say above, I think it should have
>     returned 0 only for the third test, -1 for the second test and perhaps
>     -2 for the first test?
> 
> 
> From what I can tell, here is what happens, and why (I think) you're
> receiving 0 for all three tests:
> 
>    1. You pass in half the samples as the 'bits' arg.  Speex looks at 1
>       frame worth of those bits and decodes them, decoded result in 'pcm'.
>    2. You pass in exactly 1 frame of data as the 'bits' arg.  Speex
>       looks at 1 frame worth of those bits (which is all there,
>       exactly), decodes them, stores decoded result in 'pcm'.
>    3. You pass in 2 frames of data as the 'bits' arg.  Speex looks at 1
>       frame worth of those bits (which, again, is all there), decodes
>       them, stores decoded result in 'pcm'.
> 
> When there is no more data to decode, then speex will return -1.  I'm
> also thinking that you'd need to somehow change what 'bits' points to
> (advancing the pointer to the next frame)... Or then again, I could be
> entirely wrong here -- I haven't actually written any speex_decode_int
> code myself (though I have maintained it, and the speex linkages for the
> project I've worked on). 

It sounds plausible, but doesn't seem to agree with what Jean-Marc said?

Cheers

Darren