al_create_audio_stream - Allegro 5 API
#include <allegro5/allegro_audio.h> ALLEGRO_AUDIO_STREAM *al_create_audio_stream(size_t fragment_count,
unsigned int frag_samples, unsigned int freq, ALLEGRO_AUDIO_DEPTH depth,
Creates an ALLEGRO_AUDIO_STREAM(3). The stream will be set to play by default. It will feed audio data from a buffer, which is split into a number of fragments.
- fragment_count - How many fragments to use for the audio stream. Usually only two fragments are required - splitting the audio buffer in two halves. But it means that the only time when new data can be supplied is whenever one half has finished playing. When using many fragments, you usually will use fewer samples for one, so there always will be (small) fragments available to be filled with new data.
- frag_samples - The size of a fragment in samples. See note and explanation below.
- freq - The frequency, in Hertz.
- depth - Must be one of the values listed for ALLEGRO_AUDIO_DEPTH(3).
- chan_conf - Must be one of the values listed for ALLEGRO_CHANNEL_CONF(3).
A sample that is referred to by the frag_samples parameter refers to a sequence channel intensities. E.g. if you’re making a stereo stream with the frag_samples set to 4, then the layout of the data in the fragment will be:
Where L and R are the intensities for the left and right channels respectively. A single sample, then, refers to the LR pair in this example.
The choice of fragment_count, frag_samples and freq directly influences the audio delay. The delay in seconds can be expressed as:
delay = fragment_count * frag_samples / freq
This is only the delay due to Allegro’s streaming, there may be additional delay caused by sound drivers and/or hardware.
Note: If you know the fragment size in bytes, you can get the size in samples like this:
sample_size = al_get_channel_count(chan_conf) * al_get_audio_depth_size(depth); samples = bytes_per_fragment / sample_size;
The size of the complete buffer is:
buffer_size = bytes_per_fragment * fragment_count
Note: Unlike many Allegro objects, audio streams are not implicitly destroyed when Allegro is shut down. You must destroy them manually with al_destroy_audio_stream(3) before the audio system is shut down.
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