* protect data structures that it accesses by calling SDL_LockAudio()
* and SDL_UnlockAudio() in your code. Alternately, you may pass a NULL
* pointer here, and call SDL_QueueAudio() with some frequency, to queue
- * more audio samples to be played.
+ * more audio samples to be played (or for capture devices, call
+ * SDL_DequeueAudio() with some frequency, to obtain audio samples).
* - \c desired->userdata is passed as the first parameter to your callback
* function. If you passed a NULL callback, this value is ignored.
*
/**
* Queue more audio on non-callback devices.
*
+ * (If you are looking to retrieve queued audio from a non-callback capture
+ * device, you want SDL_DequeueAudio() instead. This will return -1 to
+ * signify an error if you use it with capture devices.)
+ *
* SDL offers two ways to feed audio to the device: you can either supply a
* callback that SDL triggers with some frequency to obtain more audio
* (pull method), or you can supply no callback, and then SDL will expect
*/
extern DECLSPEC int SDLCALL SDL_QueueAudio(SDL_AudioDeviceID dev, const void *data, Uint32 len);
+/**
+ * Dequeue more audio on non-callback devices.
+ *
+ * (If you are looking to queue audio for output on a non-callback playback
+ * device, you want SDL_QueueAudio() instead. This will always return 0
+ * if you use it with playback devices.)
+ *
+ * SDL offers two ways to retrieve audio from a capture device: you can
+ * either supply a callback that SDL triggers with some frequency as the
+ * device records more audio data, (push method), or you can supply no
+ * callback, and then SDL will expect you to retrieve data at regular
+ * intervals (pull method) with this function.
+ *
+ * There are no limits on the amount of data you can queue, short of
+ * exhaustion of address space. Data from the device will keep queuing as
+ * necessary without further intervention from you. This means you will
+ * eventually run out of memory if you aren't routinely dequeueing data.
+ *
+ * Capture devices will not queue data when paused; if you are expecting
+ * to not need captured audio for some length of time, use
+ * SDL_PauseAudioDevice() to stop the capture device from queueing more
+ * data. This can be useful during, say, level loading times. When
+ * unpaused, capture devices will start queueing data from that point,
+ * having flushed any capturable data available while paused.
+ *
+ * This function is thread-safe, but dequeueing from the same device from
+ * two threads at once does not promise which thread will dequeued data
+ * first.
+ *
+ * You may not dequeue audio from a device that is using an
+ * application-supplied callback; doing so returns an error. You have to use
+ * the audio callback, or dequeue audio with this function, but not both.
+ *
+ * You should not call SDL_LockAudio() on the device before queueing; SDL
+ * handles locking internally for this function.
+ *
+ * \param dev The device ID from which we will dequeue audio.
+ * \param data A pointer into where audio data should be copied.
+ * \param len The number of bytes (not samples!) to which (data) points.
+ * \return number of bytes dequeued, which could be less than requested.
+ *
+ * \sa SDL_GetQueuedAudioSize
+ * \sa SDL_ClearQueuedAudio
+ */
+extern DECLSPEC Uint32 SDLCALL SDL_DequeueAudio(SDL_AudioDeviceID dev, void *data, Uint32 len);
+
/**
* Get the number of bytes of still-queued audio.
*
- * This is the number of bytes that have been queued for playback with
- * SDL_QueueAudio(), but have not yet been sent to the hardware.
+ * For playback device:
+ *
+ * This is the number of bytes that have been queued for playback with
+ * SDL_QueueAudio(), but have not yet been sent to the hardware. This
+ * number may shrink at any time, so this only informs of pending data.
+ *
+ * Once we've sent it to the hardware, this function can not decide the
+ * exact byte boundary of what has been played. It's possible that we just
+ * gave the hardware several kilobytes right before you called this
+ * function, but it hasn't played any of it yet, or maybe half of it, etc.
+ *
+ * For capture devices:
*
- * Once we've sent it to the hardware, this function can not decide the exact
- * byte boundary of what has been played. It's possible that we just gave the
- * hardware several kilobytes right before you called this function, but it
- * hasn't played any of it yet, or maybe half of it, etc.
+ * This is the number of bytes that have been captured by the device and
+ * are waiting for you to dequeue. This number may grow at any time, so
+ * this only informs of the lower-bound of available data.
*
* You may not queue audio on a device that is using an application-supplied
* callback; calling this function on such a device always returns 0.
- * You have to use the audio callback or queue audio with SDL_QueueAudio(),
- * but not both.
+ * You have to queue audio with SDL_QueueAudio()/SDL_DequeueAudio(), or use
+ * the audio callback, but not both.
*
* You should not call SDL_LockAudio() on the device before querying; SDL
* handles locking internally for this function.
extern DECLSPEC Uint32 SDLCALL SDL_GetQueuedAudioSize(SDL_AudioDeviceID dev);
/**
- * Drop any queued audio data waiting to be sent to the hardware.
+ * Drop any queued audio data. For playback devices, this is any queued data
+ * still waiting to be submitted to the hardware. For capture devices, this
+ * is any data that was queued by the device that hasn't yet been dequeued by
+ * the application.
*
- * Immediately after this call, SDL_GetQueuedAudioSize() will return 0 and
- * the hardware will start playing silence if more audio isn't queued.
+ * Immediately after this call, SDL_GetQueuedAudioSize() will return 0. For
+ * playback devices, the hardware will start playing silence if more audio
+ * isn't queued. Unpaused capture devices will start filling the queue again
+ * as soon as they have more data available (which, depending on the state
+ * of the hardware and the thread, could be before this function call
+ * returns!).
*
* This will not prevent playback of queued audio that's already been sent
* to the hardware, as we can not undo that, so expect there to be some
*
* You may not queue audio on a device that is using an application-supplied
* callback; calling this function on such a device is always a no-op.
- * You have to use the audio callback or queue audio with SDL_QueueAudio(),
- * but not both.
+ * You have to queue audio with SDL_QueueAudio()/SDL_DequeueAudio(), or use
+ * the audio callback, but not both.
*
* You should not call SDL_LockAudio() on the device before clearing the
* queue; SDL handles locking internally for this function.
projects / xonotic / xonotic.git / blobdiff