Fix channel reading for non-native playback

This patch fixes the playback issues in stereo file played in multichannel setup.

Now channel count is always passed as mediafile's STREAMINFO channel count. In the next steps upmixing and downmixing handled by browser side.

vlc_patches/aug/0080-fix-playback-issue-where-media-ch-different-than-out.patch

+From bcef74b8c798ccf7705b2c82fb134db84247e95f Mon Sep 17 00:00:00 2001
+From: metehan-arslan <99metehanarslan@gmail.com>
+Date: Fri, 9 Sep 2022 00:18:08 +0300
+Subject: [PATCH] fix playback issue where media ch different than output ch
+
+---
+ modules/audio_output/emscripten.c         | 15 ++++++---------
+ modules/audio_output/webaudio/webaudio.js |  1 -
+ 2 files changed, 6 insertions(+), 10 deletions(-)
+
+diff --git a/modules/audio_output/emscripten.c b/modules/audio_output/emscripten.c
+index 3317c3eb84..fc1bda1914 100644
+--- a/modules/audio_output/emscripten.c
++++ b/modules/audio_output/emscripten.c
+@@ -126,7 +126,6 @@ static void Close(vlc_object_t *obj)
+ {
+     audio_output_t *aout = (audio_output_t *) obj;
+     aout_sys_t *sys = (aout_sys_t *) aout->sys;
+-
+     free(sys->sab);
+     free(sys);
+ }
+@@ -168,27 +167,25 @@ static void Init(void *userData)
+ 
+     if (rate != sys->sample_rate)
+         sys->sample_rate = rate;
+-    if (channels != sys->channels)
+-        sys->channels = channels;
+ }
+ 
+ static int Start(audio_output_t *aout, audio_sample_format_t *restrict fmt)
+ {
+     aout_sys_t *sys = (aout_sys_t *) aout->sys;
+-    unsigned nbChannels = aout_FormatNbChannels(fmt);
+-
++    sys->channels = aout_FormatNbChannels(fmt);
+     aout_SoftVolumeStart(aout);
+-    if (( nbChannels == 0 ) || !AOUT_FMT_LINEAR(fmt))
++    if (( sys->channels == 0 ) || !AOUT_FMT_LINEAR(fmt))
+         return VLC_EGENERIC;
+     fmt->i_format = VLC_CODEC_FL32;
++    
+     if (sys->init == 0) {
+-        sys->channels = nbChannels;
+         sys->sample_rate = fmt->i_rate;
+-
++        
+         int ret = emscripten_dispatch_to_thread(
+             emscripten_main_browser_thread_id(),
+             EM_FUNC_SIG_VI,
+             Init, 0, aout );
++            
+         if (ret != 0) {
+             msg_Err(aout, "error: could not dispatch Init to main thread!");
+             return VLC_EGENERIC;
+@@ -231,7 +228,7 @@ static int Open(vlc_object_t *obj)
+     atomic_init(&sys->sab->tail, 0);
+     atomic_init(&sys->sab->can_write, 0);
+     if (unlikely (!sys->sab))
+-        return VLC_ENOMEM;    
++        return VLC_ENOMEM;
+ 
+     memset(sys->sab, 0, sizeof(webaudio_buffer_t));
+     /*
+diff --git a/modules/audio_output/webaudio/webaudio.js b/modules/audio_output/webaudio/webaudio.js
+index f291470478..4980de6399 100644
+--- a/modules/audio_output/webaudio/webaudio.js
++++ b/modules/audio_output/webaudio/webaudio.js
+@@ -84,7 +84,6 @@ mergeInto(LibraryManager.library, {
+         
+         if (audioCtx.destination.maxChannelCount < channels) {
+             console.error("Max number of channels of the browser is ", audioCtx.destination.maxChannelCount)
+-            channels = audioCtx.destination.maxChannelCount;
+         }
+ 
+         try {
+-- 
+2.37.2
+