SDL Audio: playing audio in strict mode using audio element results in error when ended

[sk-1982]

Version of emscripten/emsdk:

emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.59 (0e4c5994eb5b8defd38367a416d0703fd506ad81)
clang version 19.0.0git (https:/github.com/llvm/llvm-project df762a1643bb5b0b3c907611d118c82d4b68a39d)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: F:\Code\emsdk\upstream\bin

When emscripten is run in javascript strict mode (such as when STRICT_JS is enabled), and SDL audio is played using an audio element (such as preloaded audio with --use-preload-plugins), then the audio onended event attempts to set the read-only property paused of the audio element. This is not allowed in strict mode, and results in an error. As a result, the audio is not cleaned up and SDL will run out of channels.

Example code:

#include <SDL.h>
#include <SDL_mixer.h>
#include <emscripten/emscripten.h>

Mix_Chunk* chunk;

EMSCRIPTEN_KEEPALIVE void play_audio() {
	Mix_PlayChannel(-1, chunk, 0);
}

int main() {
	SDL_Init(SDL_INIT_AUDIO);
	Mix_OpenAudio(48000, MIX_DEFAULT_FORMAT, 1, 1024);
	chunk = Mix_LoadWAV("test.wav");
	EM_ASM(document.querySelector('#canvas').addEventListener('click', () => Module._play_audio()));
}

Compiling with emcc main.c -s USE_SDL=1 --use-preload-plugins --preload-file=test.wav -o main.html and clicking the canvas does not result in an error, as emscripten is not in strict mode.

Compiling with emcc main.c -s USE_SDL=1 -s STRICT_JS --use-preload-plugins --preload-file=test.wav -o main.html and clicking the canvas results in Uncaught TypeError: setting getter-only property "paused" when the audio ends. Clicking enough times will eventually result in the error All 32 channels in use! being logged and no further audio can be played.