AUDIO: Clarify required parameters for mixCallback.

Also, add an assert() to make invalid lengths obvious.

2 files changed, 4 insertions, 0 deletions

diff --git a/audio/mixer.cpp b/audio/mixer.cpp
index 3482bd30c9..fb4fffb8d8 100644
--- a/audio/mixer.cpp
+++ b/audio/mixer.cpp
@@ -257,6 +257,8 @@ int MixerImpl::mixCallback(byte *samples, uint len) {
 	Common::StackLock lock(_mutex);
 
 	int16 *buf = (int16 *)samples;
+	// we store stereo, 16-bit samples
+	assert(len % 4 == 0);
 	len >>= 2;
 
 	// Since the mixer callback has been called, the mixer must be ready...
diff --git a/audio/mixer_intern.h b/audio/mixer_intern.h
index 05e519c64c..a04eb55c5b 100644
--- a/audio/mixer_intern.h
+++ b/audio/mixer_intern.h
@@ -126,6 +126,8 @@ public:
 	 * the backend (e.g. from an audio mixing thread). All the actual mixing
 	 * work is done from here.
 	 *
+	 * @param samples Sample buffer, in which stereo 16-bit samples will be stored.
+	 * @param len Length of the provided buffer to fill (in bytes, should be divisible by 4).
 	 * @return number of sample pairs processed (which can still be silence!)
 	 */
 	int mixCallback(byte *samples, uint len);