[SDL] Loading data as background process

[Stephane Marchesin]

David Olofson wrote:

>>I'll
>>probably have to implement a separate thread for Ogg music
>>streaming as well though.
>>
>
>That won't be much of a problem, I think, as the decoding doesn't have 
>anything to do with SDL directly. I'd suggest using a lock-free FIFO 
>or buffer ring between the decoder thread and the audio callback.
>
Here's my 2 cents worth of music streaming with SDL :

I have done mp3 music streaming for a game. Contrary to all sane advice, 
I do decoding directly inside the callback function :)
I use an optimized mmx mp3 decoder (mpglib, to which I backported mmx 
optimizations from mpg123) and a 4096 samples buffer (this is with 44Khz 
16 bit stereo sound, I found 4096 was the minimum on windows to avoid 
sound skips with that quality, whatever I do). I know that's quite 
unreasonable but it happens to works fine on windows and linux.

The trick in all this is that the mp3 decoding time is not that big if 
you compare it to the time it takes to do a memory copy in the threaded 
decoding approach. In fact, a big part of the computation time is spent 
waiting for cache misses in both cases. It'll probably work with ogg 
too, although I couldn't find any ogg decoder that I could drop in in my 
code that was as easy to integrate as mpglib (I wanted to integrate it 
in my code to be able to add in my optimizations).

Stephane