Streaming audio from memory

[foo0]

Keep in mind that, if you pass love.audio.newSource "static" as a second argument, the sound file will be expanded into memory, so if you load a 5MB compressed .ogg file that way, it would consume ~50MB RAM when fully decompressed. Consider not using "static" in such cases.

Why not load that 5MB file into memory as it is, and stream from there, instead of hard drive? Or is it doable already? That would seem like an optimal way of doing it, as opposed to "stream from disk" (disk reads in the main loop) or "uncompress to memory" (excessive memory usage).

[slime]

That's what love.audio.newSource(filename, "stream") does right now.

[foo0]

Ah, my bad then for not checking it more thoroughly. The wiki is kind of misleading, it gives the impression that with "stream" parameter audio is streamed from disk, not loaded to memory and streamed from there.

[slime]

Yeah, I guess one reason it's ambiguously defined is so that can be added in the future if it's proven to be useful, without affecting the API.
One way to guarantee that it will always be streamed from RAM rather than the disk (although the internal implementation always does this right now anyway) is to load the file as FileData first. Something like this:

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local filedata = love.filesystem.newFileData("myaudio.ogg") -- Loads the whole file into memory.
source = love.audio.newSource(filedata, "stream")

[jjmafiae]

Is this for avoiding drive bottlenecking ?

[foo0]

@jjmafiae: In my case it's about avoiding HDD reads, analogically to why you don't usually read textures from HDD in main game loop.

Just to clarify things already said in this thread:
To play the same sound file multiple times simultaneously, each play needs its own copy of the file? E.g.:

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-- This will result in one time read of "myaudio.ogg" from disk, and 4 copies in memory?
local filedata = love.filesystem.newFileData("myaudio.ogg")
source1 = love.audio.newSource(filedata, "stream")
source2 = love.audio.newSource(filedata, "stream")
source3 = love.audio.newSource(filedata, "stream")

-- This will result in 3 times read of "myaudio.ogg" from disk, and 3 copies in memory?
source1 = love.audio.newSource("myaudio.ogg", "stream")
source2 = love.audio.newSource("myaudio.ogg", "stream")
source3 = love.audio.newSource("myaudio.ogg", "stream")

-- Example use:
love.audio.play(source1)
-- wait 1 sec
love.audio.play(source2)
-- wait 1 sec
love.audio.play(source3)

[slime]

If you do this, you will have 3 copies of the mp3 data loaded in RAM, 3 decoders (which only reference the mp3 data and allocate a small buffer of their own when streaming), and 3 unique Sources:

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source1 = love.audio.newSource("myaudio.ogg", "stream")
source2 = love.audio.newSource("myaudio.ogg", "stream")
source3 = love.audio.newSource("myaudio.ogg", "stream")

If you do this, you will have 1 copy of the mp3 data loaded in RAM, 3 decoders (which all reference the same un-decoded mp3 data), and 3 unique sources:

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local filedata = love.filesystem.newFileData("myaudio.ogg")
source1 = love.audio.newSource(filedata, "stream")
source2 = love.audio.newSource(filedata, "stream")
source3 = love.audio.newSource(filedata, "stream")

In general there aren't a lot of reasons to have multiple copies of the same streaming source. If you have a short sound file that will be played many times, you should create a static source. Static sources only decode the audio once per source (when it's initially loaded), whereas streaming sources will decode the same thing every time, if you play it back several times.

As of LÖVE 0.9.1, you can use [wiki]Source:clone[/wiki], which will be as efficient as method #2 above for streaming sources, and more efficient than that for static sources - it won't create a separate copy of the decoded (raw PCM) data with static sources, so it uses less RAM.

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source1 = love.audio.newSource("myaudio.ogg", "static")
source2 = source1:clone()
source3 = source1:clone()

[jjmafiae]

can textures be streamed from memory too ?

[slime]

You can use Image:getData to get the ImageData which was used to create the Image. If you modify that ImageData, you can use Image:refresh to apply the changes.

[foo0]

Thanks for detailed explanation. This clone() mechanics seems to be the way.

Is it possible to check the length (duration) of a sound source (either stream or static)?