SDL2 ，clear the queue data?

[MrJokerBoy]

In the SDL2 version, when playing through callback, is there a way to clear the queue data?

[slouken]

No, the callback function is called on demand, there is no queue involved.

[MrJokerBoy]

@slouken Now there is a problem. After the queue data is filled, after pausing and doing some seek operations, the previously stored queue data will be played back when playing again. I hope that the data will be cleared and the new data that is passed in will be played directly. .

[slouken]

Are you talking about SDL2 or SDL3?

[MrJokerBoy]

@slouken SDL2 version 2.28.3

[slouken]

What operating system and SDL audio driver are you using?

[MrJokerBoy]

iOS version of SDL used

[slouken]

@icculus, do we have an issue on iOS where we pause the device but don't flush the audio in SDL2?

[icculus]

As far as I know, it should be requesting audio on demand; it's possible it's buffering a little bit for resampling...?

So to be clear, is the problem:

• The audio callback runs, you feed it data, then
• you pause the device with SDL_PauseAudioDevice
• sometime later you unpause it
• it then plays old audio from before the pause

?

(And if this is correct, how much old audio does it play?)

[icculus]

Actually, I can see that the comment I made about resampling is obviously going to cause this problem, so I've pushed a fix for that. If this doesn't fix your actual problem, please let me know!

[icculus]

(This specific fix doesn't need to be cherry-picked to SDL3, since it works differently here and shouldn't have this bug.)

[MrJokerBoy]

@icculus Hello, I have tried it and the problem still exists. I will add the screen recording file. The steps are as follows:

1. Play normally to a certain position
2. seek the head
3. Play again
   Some data at the end of the last queue will be played, and sometimes the sound will be loud.

RPReplay_Final1699323725.MP4

[icculus]

This is working here. I modified SDL/test/loopwave.c like this:

diff --git a/test/loopwave.c b/test/loopwave.c
index 18bb0ad74..aec352807 100644
--- a/test/loopwave.c
+++ b/test/loopwave.c
@@ -120,11 +120,13 @@ int main(int argc, char *argv[])
     SDL_LogSetPriority(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_INFO);

     /* Load the SDL library */
-    if (SDL_Init(SDL_INIT_AUDIO | SDL_INIT_EVENTS) < 0) {
+    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_EVENTS) < 0) {
         SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "Couldn't initialize SDL: %s\n", SDL_GetError());
         return 1;
     }

+SDL_CreateWindow("Hello SDL", 100, 100, 100, 100, 0);
+
     filename = GetResourceFilename(argc > 1 ? argv[1] : NULL, "sample.wav");

     if (!filename) {
@@ -166,6 +168,15 @@ int main(int argc, char *argv[])
                 (event.type == SDL_AUDIODEVICEREMOVED && !event.adevice.iscapture && event.adevice.which == device)) {
                 reopen_audio();
             }
+
+            if ((event.type == SDL_KEYDOWN) && (event.key.keysym.sym == SDLK_SPACE)) {
+                if (SDL_GetAudioDeviceStatus(device) == SDL_AUDIO_PAUSED) {
+                    SDL_PauseAudioDevice(device, 0);
+                } else {
+                    SDL_PauseAudioDevice(device, 1);
+                    wave.soundpos = 0;  /* reset to start */
+                }
+            }
         }
         SDL_Delay(100);
     }

So the app starts and you can press the spacebar to pause/unpause. After pausing, it resets the position of the .wav file it's playing to the beginning, so we can hear clearly if an old buffer is still pending. It works.

Granted, this on macOS, not iOS, so it uses the same audio code but it's possible something else is different, but it seems unlikely.

My current assumption is that the app is holding a buffer after pausing and sending it on to SDL, incorrectly, the next time the callback runs after unpausing. If your app has source code available, I can take a look to see if I can debug this further, but at this moment, I don't think there's a further issue in SDL itself.

(Closing this issue, but we can reopen it if necessary!)