lavf/isom: support for demuxing and remuxing of MPEG-H 3D Audio in MP4

Implemented according to the specification at https://www.iso.org/standard/69561.html
The 'mhm1' sample entry is registered with MP4RA, which is defined as MHAS encapsulated single stream MPEG-H 3D Audio.
'MHAS' stands for MPEG-H audio stream, which contains encoded audio data and corresponds metadata for decoding.
This patch enables extracting the MHAS bitstream from MP4 and remuxing into MP4.
Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/isom.c

@@ -371,6 +371,7 @@ const AVCodecTag ff_codec_movaudio_tags[] = {
     { AV_CODEC_ID_FLAC,            MKTAG('f', 'L', 'a', 'C') }, /* nonstandard */
     { AV_CODEC_ID_TRUEHD,          MKTAG('m', 'l', 'p', 'a') }, /* mp4ra.org */
     { AV_CODEC_ID_OPUS,            MKTAG('O', 'p', 'u', 's') }, /* mp4ra.org */
+    { AV_CODEC_ID_MPEGH_3D_AUDIO,  MKTAG('m', 'h', 'm', '1') }, /* MPEG-H 3D Audio bitstream */
     { AV_CODEC_ID_NONE, 0 },
 };
 

libavformat/movenc.c

@@ -2493,6 +2493,7 @@ static int mov_write_stbl_tag(AVFormatContext *s, AVIOContext *pb, MOVMuxContext
     mov_write_stts_tag(pb, track);
     if ((track->par->codec_type == AVMEDIA_TYPE_VIDEO ||
          track->par->codec_id == AV_CODEC_ID_TRUEHD ||
+         track->par->codec_id == AV_CODEC_ID_MPEGH_3D_AUDIO ||
          track->par->codec_tag == MKTAG('r','t','p',' ')) &&
         track->has_keyframes && track->has_keyframes < track->entry)
         mov_write_stss_tag(pb, track, MOV_SYNC_SAMPLE);
@@ -6875,6 +6876,7 @@ const AVCodecTag codec_mp4_tags[] = {
     { AV_CODEC_ID_DVD_SUBTITLE, MKTAG('m', 'p', '4', 's') },
     { AV_CODEC_ID_MOV_TEXT    , MKTAG('t', 'x', '3', 'g') },
     { AV_CODEC_ID_BIN_DATA    , MKTAG('g', 'p', 'm', 'd') },
+    { AV_CODEC_ID_MPEGH_3D_AUDIO, MKTAG('m', 'h', 'm', '1') },
     { AV_CODEC_ID_NONE        ,    0 },
 };