SDL_mixer 1.2: fix Mix_PlayChannel audio 'leaking'; fix onended callback to correctly update audio status (#22581)

### Mix_PlayChannel audio 'leaking'
Hi, I found a bug while using builtin SDL_mixer 1.2. 
You can play many sounds on same channel in case if you do not manuall
halt it before.

Reagrding to
[documentation](https://wiki.libsdl.org/SDL2_mixer/Mix_PlayChannel) of
SDL:
> If a specific channel was requested, and there is a chunk already
playing there, that chunk will be halted and the new chunk will take its
place.


So, when you call
```
Mix_PlayChannel(channel, sound, loops);
```

It shoud internally halt the channel. Current emscripten implemntation
is wrong, the previously runned chunk on that channel continue to play.

You can easily reporoduce this with code:

```c++
/* 
compile with:
emcc main.cpp -o main.html --preload-file "./@"
*/   
#include <SDL/SDL_mixer.h>
#include <chrono>
#include <emscripten.h>

Mix_Chunk* chunk = nullptr;
uint64_t lastRun = 0;

void loop() {
    using namespace std::chrono;
    uint64_t now = duration_cast<milliseconds>(system_clock::now().time_since_epoch()).count();
    if (now - lastRun > 5000) {
        Mix_PlayChannel(0, chunk, -1);
        lastRun = now;
    }
}

int main(int argc, char** argv) {
    if ((Mix_Init(MIX_INIT_OGG) & MIX_INIT_OGG) != MIX_INIT_OGG) {
      printf("ERR! Mix_Init: Failed to init with required flags support!\n");
      printf("ERR! Mix_Init: %s\n", Mix_GetError());
      return -1;
    }

    if (Mix_OpenAudio(MIX_DEFAULT_FREQUENCY, MIX_DEFAULT_FORMAT, 1, 1024) == -1) {
      printf("ERR! Mix_OpenAudio: %s\n", Mix_GetError());
      return -1;
    }

    Mix_AllocateChannels(1);
    chunk = Mix_LoadWAV("/music.ogg");
    emscripten_set_main_loop(loop, 0, false);
    return 0;
}
```

If you compile and run it then you will hear infinite looping of
music.ogg, and every 5 sec new one is started.

I fixed this by calling Mix_HaltChannel if channel is playing audio.

### fix onended callback to correctly update audio status

Found another issue in SDL_mixer implementation. Current implementation
does not detect playing status of sounds correctly (`Mix_Playing`,
`Mix_PlayingMusic`). This happens because in on `onended` callback
comparsion with `this` works only for case when audio created by cloning
audio node, otherwise comparsion should be against audio.webAudioNode.

Author: caiiiycuk

src/library_sdl.js

@@ -2821,6 +2821,7 @@ var LibrarySDL = {
   Mix_ReserveChannels: (num) => {
     SDL.channelMinimumNumber = num;
   },
+  Mix_PlayChannelTimed__deps: ['Mix_HaltChannel'],
   Mix_PlayChannelTimed__proxy: 'sync',
   Mix_PlayChannelTimed: (channel, id, loops, ticks) => {
     // TODO: handle fixed amount of N loops. Currently loops either 0 or infinite times.
@@ -2864,9 +2865,14 @@ var LibrarySDL = {
       audio.frequency = info.audio.frequency;
     }
     audio['onended'] = function() { // TODO: cache these
-      if (channelInfo.audio == this) { channelInfo.audio.paused = true; channelInfo.audio = null; }
+      if (channelInfo.audio === this || channelInfo.audio.webAudioNode === this) { 
+        channelInfo.audio.paused = true; channelInfo.audio = null; 
+      }
       if (SDL.channelFinished)  {{{ makeDynCall('vi', 'SDL.channelFinished') }}}(channel);
     }
+    if (channelInfo.audio) {
+      _Mix_HaltChannel(channel);
+    }
     channelInfo.audio = audio;
     // TODO: handle N loops. Behavior matches Mix_PlayMusic
     audio.loop = loops != 0;
@@ -2946,7 +2952,11 @@ var LibrarySDL = {
     } else if (info.audio) { // Play via the <audio> element
       audio = info.audio;
     }
-    audio['onended'] = function() { if (SDL.music.audio == this) _Mix_HaltMusic(); } // will send callback
+    audio['onended'] = function() { 
+      if (SDL.music.audio === this || SDL.music.audio?.webAudioNode === this) {
+        _Mix_HaltMusic(); // will send callback
+      }
+    }
     audio.loop = loops != 0 && loops != 1; // TODO: handle N loops for finite N
     audio.volume = SDL.music.volume;
     SDL.music.audio = audio;

test/browser/test_sdl_audio_mix_channels_halt.c

@@ -0,0 +1,42 @@
+#include <SDL/SDL_mixer.h>
+#include <emscripten.h>
+
+Mix_Chunk* chunk = 0;
+uint64_t started = 0;
+uint64_t lastRun = 0;
+
+void loop() {
+  uint64_t now = emscripten_get_now();
+  if (now - lastRun > 300) {
+    Mix_PlayChannel(0, chunk, -1);
+    lastRun = now;
+  }
+  if (now - started > 3000) {
+    emscripten_force_exit(0);
+  }
+}
+
+int main(int argc, char** argv) {
+  if ((Mix_Init(MIX_INIT_OGG) & MIX_INIT_OGG) != MIX_INIT_OGG) {
+    printf("ERR! Mix_Init: Failed to init with required flags support!\n");
+    printf("ERR! Mix_Init: %s\n", Mix_GetError());
+    return 1;
+  }
+
+  if (Mix_OpenAudio(MIX_DEFAULT_FREQUENCY, MIX_DEFAULT_FORMAT, 1, 1024) == -1) {
+    printf("ERR! Mix_OpenAudio: %s\n", Mix_GetError());
+    return 1;
+  }
+
+  Mix_AllocateChannels(1);
+  chunk = Mix_LoadWAV("/the_entertainer.ogg");
+  if (!chunk) {
+    printf("ERR! Mix_LoadWAV: %s\n", Mix_GetError());
+    return 1;
+  }
+
+  printf("The sound should reset to start every 300ms, if you hear overapplied music then the test has failed.\n");
+  started =  emscripten_get_now();
+  emscripten_set_main_loop(loop, 0, 0);
+  return 0;
+}

test/browser/test_sdl_audio_mix_playing.c

@@ -0,0 +1,42 @@
+#include <SDL/SDL_mixer.h>
+#include <emscripten.h>
+
+Mix_Chunk* chunk = 0;
+uint64_t started = 0;
+
+void loop() {
+  uint64_t now = emscripten_get_now();
+  if (now - started > 2000) {
+    // length of sound is 1sec
+    printf("isPlaying? %s\n", Mix_Playing(0) ? "yes" : "no");
+    emscripten_force_exit(Mix_Playing(0) ? 1 : 0);
+  }
+}
+
+int main(int argc, char** argv) {
+  if ((Mix_Init(MIX_INIT_OGG) & MIX_INIT_OGG) != MIX_INIT_OGG) {
+    printf("ERR! Mix_Init: Failed to init with required flags support!\n");
+    printf("ERR! Mix_Init: %s\n", Mix_GetError());
+    return 1;
+  }
+
+  if (Mix_OpenAudio(MIX_DEFAULT_FREQUENCY, MIX_DEFAULT_FORMAT, 1, 1024) == -1) {
+    printf("ERR! Mix_OpenAudio: %s\n", Mix_GetError());
+    return 1;
+  }
+
+  Mix_AllocateChannels(1);
+  chunk = Mix_LoadWAV("/noise.ogg");
+  if (!chunk) {
+    printf("ERR! Mix_LoadWAV: %s\n", Mix_GetError());
+    return 1;
+  }
+  Mix_PlayChannel(0, chunk, 0);
+  if (!Mix_Playing(0)) {
+    printf("ERR! Channel is not playing\n");
+    return 1;
+  }
+  started = emscripten_get_now();
+  emscripten_set_main_loop(loop, 0, 0);
+  return 0;
+}

test/test_interactive.py

@@ -82,6 +82,16 @@ def test_sdl_audio_mix_channels(self, args):
 
     self.btest_exit('test_sdl_audio_mix_channels.c', args=['-O2', '--minify=0', '--preload-file', 'sound.ogg'] + args)
 
+  def test_sdl_audio_mix_channels_halt(self):
+    shutil.copy(test_file('sounds/the_entertainer.ogg'), '.')
+
+    self.btest_exit('test_sdl_audio_mix_channels_halt.c', args=['-O2', '--minify=0', '--preload-file', 'the_entertainer.ogg'])
+
+  def test_sdl_audio_mix_playing(self):
+    shutil.copy(test_file('sounds/noise.ogg'), '.')
+
+    self.btest_exit('test_sdl_audio_mix_playing.c', args=['-O2', '--minify=0', '--preload-file', 'noise.ogg'])
+
   @parameterized({
     '': ([],),
     'wasmfs': (['-sWASMFS'],),