[Speex-dev] Decoding only a certain frame results in different values than when decoding the entire file

Steve Checkoway s at pahtak.org
Fri Dec 23 10:17:41 PST 2011

On Dec 23, 2011, at 10:03 , Hermann Weber wrote:

> I found out something:
> The more frames I decode before the frame that I actually want to
> decode, the better the quality becomes.
> For example when I basically want to decode frame #100, I read frame  
> #80
> to #100, and then frame 100 has the quality that I need.
> Why? Is there any information on this behaviour?

Speex is a stateful encoder. As it encodes the audio, the state  
changes. As it decodes, the state changes. You're trying to start  
somewhere in the middle with the initial state rather than with the  
state it would have if you started from the beginning and decoded it  
all. As you've noticed, it can recover from lost frames over time.

This is just repeating what Lakhdar Bourokba already said though.

As for your question about the header, it really depends on how you're  
saving the encoded file.

Steve Checkoway

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