sound-streaming.md

title	brief
Sound Streaming in Defold	This manual explains how to stream sounds into the Defold game engine

Sound Streaming

While the default behaviour is to load sound data in full, it may also be beneficial to load the data in chunks, prior to their use. This is often called "streaming".

One benefit of sound streaming is that less runtime memory is required, another is if you are streaming content from e.g. a http url, you can update the content at any time, and also avoid the initial download.

Example

There is an example project showcasing this setup: https://github.com/defold/example-sound-streaming

How to enable streaming sounds

Easy way

The simplest way to use sound streaming, is by enabling the sound.stream_enabled setting in game.project. When this option is enabled the engine will start streaming the sounds.

Note: If you have lots of sound files loaded at the same time, you may need to increase the sound.stream_cache_size value (see below).

Runtime resources

You can also create a new sound data resource, and set it to a sound component.

You do this by:

• Load the initial part of the sound file data
  • Note: This is the raw sound file, including the ogg/wav header
• Create a new sound data resource by calling resource.create_sound_data().
• Set the new sound data resource to the sound component using go.set()

Here is an excerpt from the example project, using a http.request() to get the initial sound file.

::: sidenote The web server you're loading content from has to support HTTP range requests. :::

local function play_sound(self, hash)
    go.set(self.component, "sound", hash) -- override the resource data on the component
    sound.play(self.component)            -- start playing the sound
end

local function parse_range(s)
    local _, _, rstart, rend, size = string.find(s, "(%d+)-(%d+)/(%d+)") -- "bytes 0-16383/103277"
    return rstart, rend, size
end

-- Callback for the http response.
local function http_result(self, _id, response, extra)
    if response.status == 200 or response.status == 206 then
        -- Successful request
        local relative_path = self.filename
        local range = response.headers['content-range'] -- content-range = "bytes 0-16383/103277"
        local rstart, rend, filesize = parse_range(range)
        -- Create the Defold resource
        --   "partial" will enable the streaming mode
        print("Creating resource", relative_path)
        local hash = resource.create_sound_data(relative_path, { data = response.response, filesize = filesize, partial = true })
        -- send "play_sound" to the component
        play_sound(self, hash)
    end
end

local function load_web_sound(base_url, relative_path)
    local url = base_url .. "/" .. relative_path
    local headers = {}
    headers['Range'] = string.format("bytes=%d-%d", 0, 16384-1)

    http.request(url, "GET", http_result, headers, nil, { ignore_cache = true })
end

Resource providers

You can use other means to load the initial chunk of the sound file. The important thing to remember is that the rest of the chunks are loaded from the resource system and its resource providers. In this example, we add a new (http) file provider by adding a live update mount, by calling using liveupdate.add_mount().

You can find a working example in https://github.com/defold/example-sound-streaming.

-- See http_result() from above example

local function load_web_sound(base_url, relative_path)
    local url = base_url .. "/" .. relative_path
    local headers = {}
    -- Request the initial part of the file
    headers['Range'] = string.format("bytes=%d-%d", 0, 16384-1)

    http.request(url, "GET", http_result, headers, nil, { ignore_cache = true })
end

function init(self)
    self.base_url = "http://my.server.com"
    self.filename = "/path/to/sound.ogg"

    liveupdate.add_mount("webmount", self.base_url, 100, function ()
                    -- once the mount is ready, we can start our request for downloading the first chunk
                    load_web_sound(self.base_url, self.filename)
                end)
end

function final(self)
    liveupdate.remove_mount("webmount")
end

Sound chunk cache

The amount of memory consumed by the sounds at runtime is controlled by the sound.stream_cache_size setting in game.project. Given this limit, the loaded sound data will never exceed this limit.

The initial chunk of each sound file cannot be evicted and they will occupy the cache for as long as the resources are loaded. The size of the initial chunk is controlled by the sound.stream_preload_size setting in game.project.

You can also control the size of each sound chunk by changing the sound.stream_chunk_size setting in game.project. This may help you get the sound cache size down even further if you have many sound files loaded at the same time. Sound files smaller than the sound chunk size, aren't streamed and if a new chunk doesn't fit into the cache, the oldest chunk is evicted

::: important The total size of the sound chunk cache should be larger than the number of loaded sound files times the stream chunk size. Otherwise, you risk evicting new chunks each frame and sounds won't play properly :::