Add a configuration option Module.SDL_numSimultaneouslyQueuedBuffers to allow user code to configure how many SDL audio buffers to keep simultaneously queued up for the audio backend. More buffers means less change of starving (and cracking audio), but increases latency. Fewer buffers lower the latency at the risk of playback glitches. Make minimum audio buffer size 128, which should be way below anything reasonable already. Clean up commented out code.

1 files changed, 13 insertions, 9 deletions

diff --git a/src/library_sdl.js b/src/library_sdl.js
index e69009af..e2ad82d6 100644
--- a/src/library_sdl.js
+++ b/src/library_sdl.js
@@ -1469,7 +1469,7 @@ var LibrarySDL = {
       } else if (SDL.audio.channels != 1 && SDL.audio.channels != 2) { // Unsure what SDL audio spec supports. Web Audio spec supports up to 32 channels.
         console.log('Warning: Using untested number of audio channels ' + SDL.audio.channels);
       }
-      if (SDL.audio.samples < 512 || SDL.audio.samples > 524288 /* arbitrary cap */) {
+      if (SDL.audio.samples < 128 || SDL.audio.samples > 524288 /* arbitrary cap */) {
         throw 'Unsupported audio callback buffer size ' + SDL.audio.samples + '!';
       } else if ((SDL.audio.samples & (SDL.audio.samples-1)) != 0) {
         throw 'Audio callback buffer size ' + SDL.audio.samples + ' must be a power-of-two!';
@@ -1482,7 +1482,7 @@ var LibrarySDL = {
       
       // To account for jittering in frametimes, always have multiple audio buffers queued up for the audio output device.
       // This helps that we won't starve that easily if a frame takes long to complete.
-      SDL.audio.numSimultaneouslyQueuedBuffers = 3;
+      SDL.audio.numSimultaneouslyQueuedBuffers = Module['SDL_numSimultaneouslyQueuedBuffers'] || 3;
       
       // Create a callback function that will be routinely called to ask more audio data from the user application.
       SDL.audio.caller = function SDL_audio_caller() {
@@ -1519,9 +1519,11 @@ var LibrarySDL = {
           
           // Compute when the next audio callback should be called.
           var curtime = Date.now() / 1000.0 - SDL.audio.startTime;
-//          if (curtime > SDL.audio.nextPlayTime && SDL.audio.nextPlayTime != 0) {
-//            console.log('warning: Audio callback had starved sending audio by ' + (curtime - SDL.audio.nextPlayTime) + ' seconds.');
-//          }
+#if ASSERTIONS
+          if (curtime > SDL.audio.nextPlayTime && SDL.audio.nextPlayTime != 0) {
+            console.log('warning: Audio callback had starved sending audio by ' + (curtime - SDL.audio.nextPlayTime) + ' seconds.');
+          }
+#endif
           var playtime = Math.max(curtime, SDL.audio.nextPlayTime);
           var buffer_duration = SDL.audio.samples / SDL.audio.freq;
           SDL.audio.nextPlayTime = playtime + buffer_duration;
@@ -1533,7 +1535,7 @@ var LibrarySDL = {
             ++SDL.audio.numAudioTimersPending;
             Browser.safeSetTimeout(SDL.audio.caller, 1.0);
           }
-       }
+        }
       } else {
         // Initialize Web Audio API if we haven't done so yet. Note: Only initialize Web Audio context ever once on the web page,
         // since initializing multiple times fails on Chrome saying 'audio resources have been exhausted'.
@@ -1595,9 +1597,11 @@ var LibrarySDL = {
             // Schedule the generated sample buffer to be played out at the correct time right after the previously scheduled
             // sample buffer has finished.
             var curtime = SDL.audioContext['currentTime'];
-//            if (curtime > SDL.audio.nextPlayTime && SDL.audio.nextPlayTime != 0) {
-//              console.log('warning: Audio callback had starved sending audio by ' + (curtime - SDL.audio.nextPlayTime) + ' seconds.');
-//            }
+#if ASSERTIONS
+            if (curtime > SDL.audio.nextPlayTime && SDL.audio.nextPlayTime != 0) {
+              console.log('warning: Audio callback had starved sending audio by ' + (curtime - SDL.audio.nextPlayTime) + ' seconds.');
+            }
+#endif
             var playtime = Math.max(curtime, SDL.audio.nextPlayTime);
             SDL.audio.soundSource[SDL.audio.nextSoundSource]['start'](playtime);
             var buffer_duration = sizeSamplesPerChannel / SDL.audio.freq;