On Wednesday 03 June 2009 11:33:27 pm Mik Fig wrote:
> I have a question inspired by qartar's problem with streaming to the
> buffers. I was wondering what kind of performance benefits might result
> from streaming blocks of data rather than uploading the entire sound file.
> In what cases might such a solution have great benefit and in what
> situations might it just be useless?
Streaming is mostly helpful for when the sound is large (at least a few
megabytes uncompressed), since it doesn't have to hold the whole uncompressed
file in memory, or read/decompress the whole file at once before playback can
start. Hardware devices can have memory restrictions, too.
Some implementations may also have restrictions that can cause integer
overflows.. eg. if the current position of a sound is tracked using a 22.10
fixed-point integer, that only leaves 22 bits to represent the whole-sample
position. 22 bits can hold a value up to 4,194,304, so a buffer that has more
than a couple million samples may risk having the position value overflow and
wrap around back to 0 before it can finish.. or the end point itself can wrap
around, so only part of the beginning is played before stopping.
Shorter sounds won't really benefit from streaming though, and may actually be
a detriment, if the overhead of buffer queues and such are more costly than
simply loading it all at once. Streaming is also detrimental because the
buffers can't be as easily reused and shared among multiple sources.
IMO, most regular sound effects would be better not streamed, so they can be
cached in an OpenAL buffer for quick reuse. Music and long dialog may be
better streamed, since they're going to be larger and more unique (they won't
be reused as often for caching to be any real benefit).
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