Abstract base class for streamed audio sources
Unlike audio buffers (see
SF::SoundBuffer), audio streams
are never completely loaded in memory. Instead, the audio
data is acquired continuously while the stream is playing.
This behavior allows to play a sound with no loading delay,
and keeps the memory consumption very low.
Sound sources that need to be streamed are usually big files (compressed audio musics that would eat hundreds of MB in memory) or files that would take a lot of time to be received (sounds played over the network).
SF::SoundStream is a base class that doesn't care about the
stream source, which is left to the derived class. SFML provides
a built-in specialization for big files (see
No network stream source is provided, but you can write your own
by combining this class with the network module.
A derived class has to override two virtual functions:
- on_get_data fills a new chunk of audio data to be played
- on_seek changes the current playing position in the source
It is important to note that each SoundStream is played in its own separate thread, so that the streaming loop doesn't block the rest of the program. In particular, the OnGetData and OnSeek virtual functions may sometimes be called from this separate thread. It is important to keep this in mind, because you may have to take care of synchronization issues if you share data between threads.
class CustomStream < SF::SoundStream
def initialize(location : String)
# Open the source and get audio settings
# Initialize the stream -- important!
# Return a slice with audio data from the stream source
# (note: must not be empty if you want to continue playing)
# Change the current position in the stream source
stream = CustomStream.new("path/to/stream")
Direct known subclasses
NoLoop = -1#
"Invalid" end_seeks value, telling us to continue uninterrupted
.new(channel_count : Int, sample_rate : Int)#
Define the audio stream parameters
This function must be called by derived classes as soon as they know the audio settings of the stream to play. Any attempt to manipulate the stream (play(), ...) before calling this function will fail. It can be called multiple times if the settings of the audio stream change, but only when the stream is stopped.
- channel_count - Number of channels of the stream
- sample_rate - Sample rate, in samples per second
#channel_count : Int32#
Return the number of channels of the stream
1 channel means a mono sound, 2 means stereo, etc.
Returns: Number of channels
#loop : Bool#
Tell whether or not the stream is in loop mode
Returns: True if the stream is looping, false otherwise
#loop=(loop : Bool)#
Set whether or not the stream should loop after reaching the end
If set, the stream will restart from beginning after reaching the end and so on, until it is stopped or loop=(false) is called. The default looping state for streams is false.
- loop - True to play in loop, false to play once
#on_get_data : Slice(Int16) | ::Nil#
Request a new chunk of audio samples from the stream source
This function must be overridden by derived classes to provide the audio samples to play. It is called continuously by the streaming loop, in a separate thread. The source can choose to stop the streaming loop at any time, by returning false to the caller. If you return true (i.e. continue streaming) it is important that the returned array of samples is not empty; this would stop the stream due to an internal limitation.
- data - Chunk of data to fill
Returns: True to continue playback, false to stop
#on_loop : Int64#
Change the current playing position in the stream source to the beginning of the loop
This function can be overridden by derived classes to
allow implementation of custom loop points. Otherwise,
it just calls
on_seek(Time::Zero) and returns 0.
Returns: The seek position after looping (or -1 if there's no loop)
Change the current playing position in the stream source
This function must be overridden by derived classes to allow random seeking into the stream source.
- time_offset - New playing position, relative to the beginning of the stream
Pause the audio stream
This function pauses the stream if it was playing, otherwise (stream already paused or stopped) it has no effect.
Start or resume playing the audio stream
This function starts the stream if it was stopped, resumes it if it was paused, and restarts it from the beginning if it was already playing. This function uses its own thread so that it doesn't block the rest of the program while the stream is played.
#playing_offset : Time#
Get the current playing position of the stream
Returns: Current playing position, from the beginning of the stream
Change the current playing position of the stream
The playing position can be changed when the stream is either paused or playing. Changing the playing position when the stream is stopped has no effect, since playing the stream would reset its position.
- time_offset - New playing position, from the beginning of the stream
Set the processing interval
The processing interval controls the period at which the audio buffers are filled by calls to on_get_data. A smaller interval may be useful for low-latency streams. Note that the given period is only a hint and the actual period may vary. The default processing interval is 10 ms.
- interval - Processing interval
#sample_rate : Int32#
Get the stream sample rate of the stream
The sample rate is the number of audio samples played per second. The higher, the better the quality.
Returns: Sample rate, in number of samples per second
#status : SoundSource::Status#
Get the current status of the stream (stopped, paused, playing)
Returns: Current status