Trying to fix MP4 audio playback in-browser

Author: wberube

src/media.c

@@ -490,7 +490,7 @@ int enable_mp4(void) {
 
         mp4_set_config(app_config.mp4_width, app_config.mp4_height, app_config.mp4_fps,
             app_config.audio_enable ? HAL_AUDCODEC_MP3 : HAL_AUDCODEC_UNSPEC, 
-            app_config.audio_bitrate, app_config.audio_srate);
+            app_config.audio_bitrate, 1, app_config.audio_srate);
     }
 
     if (ret = bind_channel(index, app_config.mp4_fps, 0))

src/mp4/moov.c

@@ -553,7 +553,7 @@ enum BufError write_btrt(struct BitBuf *ptr, const struct MoovInfo *moov_info) {
     chk_err; // 4 Buffer size
     err = put_u32_be(ptr, moov_info->audio_bitrate * 1000);
     chk_err; // 4 Max bitrate
-    err = put_u32_be(ptr, moov_info->audio_bitrate * 1000);
+    err = put_u32_be(ptr, moov_info->audio_bitrate * 1000 - 1);
     chk_err; // 4 Avg bitrate
     err = put_u32_be_to_offset(ptr, start_atom, ptr->offset - start_atom);
     chk_err;
@@ -619,7 +619,7 @@ enum BufError write_DecoderConfig(struct BitBuf *ptr, const struct MoovInfo *moo
     chk_err; // 3 bufferSize
     err = put_u32_be(ptr, moov_info->audio_bitrate * 1000);
     chk_err; // 4 Max bitrate
-    err = put_u32_be(ptr, moov_info->audio_bitrate * 1000);
+    err = put_u32_be(ptr, moov_info->audio_bitrate * 1000 - 1);
     chk_err; // 4 Avg bitrate
     err = put_u32_le_to_offset(ptr, var_len, varint32(ptr->offset - var_len - 4));
     chk_err;
@@ -675,7 +675,7 @@ enum BufError write_TagAudioSpecificConfig(
         bitstream |= moov_info->audio_samplerate;
         used_bits += 24;
     }
-    int channels = 1;
+    int channels = moov_info->audio_channels;
     bitstream <<= 4;
     bitstream |= channels;
     used_bits += 4;
@@ -768,7 +768,7 @@ enum BufError write_mp4a(struct BitBuf *ptr, const struct MoovInfo *moov_info) {
     chk_err; // 1 dataref index
     err = put_skip(ptr, 8);
     chk_err; // 8 reserved
-    err = put_u16_be(ptr, 2);
+    err = put_u16_be(ptr, moov_info->audio_channels);
     chk_err; // 2 channel count
     err = put_u16_be(ptr, 16);
     chk_err; // 2 sample size

src/mp4/moov.h

@@ -5,6 +5,7 @@
 struct MoovInfo {
     char audio_codec;
     unsigned short audio_bitrate;
+    unsigned char audio_channels;
     unsigned int audio_samplerate;
     char is_h265;
     uint8_t profile_idc;

src/mp4/mp4.c

@@ -8,6 +8,7 @@ uint32_t default_sample_size = 40000;
 
 unsigned int aud_samplerate = 0;
 unsigned short aud_bitrate = 0;
+char aud_channels = 0;
 short vid_width = 1920, vid_height = 1080;
 char aud_codec = 0, vid_framerate = 30;
 
@@ -35,6 +36,8 @@ enum BufError create_header(char is_h265) {
     struct MoovInfo moov_info;
     memset(&moov_info, 0, sizeof(struct MoovInfo));
     moov_info.audio_codec = aud_codec;
+    moov_info.audio_bitrate = aud_bitrate;
+    moov_info.audio_channels = aud_channels;
     moov_info.audio_samplerate = aud_samplerate;
     moov_info.is_h265 = is_h265 & 1;
     moov_info.profile_idc = 100;
@@ -59,13 +62,14 @@ enum BufError create_header(char is_h265) {
     chk_err return BUF_OK;
 }
 
-void mp4_set_config(short width, short height, char framerate,
-    char acodec, unsigned short bitrate, unsigned int srate) {
+void mp4_set_config(short width, short height, char framerate, char acodec,
+    unsigned short bitrate, char channels, unsigned int srate) {
     vid_width = width;
     vid_height = height;
     vid_framerate = framerate;
     aud_codec = acodec;
     aud_bitrate = bitrate;
+    aud_channels = channels;
     aud_samplerate = srate;
 }
 

src/mp4/mp4.h

@@ -25,8 +25,8 @@ struct Mp4State {
     uint32_t nals_count;
 };
 
-void mp4_set_config(short width, short height, char framerate,
-    char acodec, unsigned short bitrate, unsigned int srate);
+void mp4_set_config(short width, short height, char framerate, char acodec,
+    unsigned short bitrate, char channels, unsigned int srate);
 
 void mp4_set_sps(const char *nal_data, const uint32_t nal_len, char is_h265);
 void mp4_set_pps(const char *nal_data, const uint32_t nal_len, char is_h265);