avformat/iamf: byteswap values in OpusHeader

Clause 3.11.1 of IAMF[1] states the values are stored in big endian, in
contrast to the Ogg Encapsulation for Opus[2] where they are in little endian.

[1]https://aomediacodec.github.io/iamf/v1.0.0-errata.html#opus-specific
[2]https://datatracker.ietf.org/doc/html/rfc7845#section-5.1

Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/iamf_parse.c

@@ -272,6 +272,9 @@ static int update_extradata(AVCodecParameters *codecpar)
     switch(codecpar->codec_id) {
     case AV_CODEC_ID_OPUS:
         AV_WB8(codecpar->extradata + 9, codecpar->ch_layout.nb_channels);
+        AV_WL16(codecpar->extradata + 10, AV_RB16(codecpar->extradata + 10)); // Byte swap pre-skip
+        AV_WL32(codecpar->extradata + 12, AV_RB32(codecpar->extradata + 12)); // Byte swap sample rate
+        AV_WL16(codecpar->extradata + 16, AV_RB16(codecpar->extradata + 16)); // Byte swap Output Gain
         break;
     case AV_CODEC_ID_AAC: {
         uint8_t buf[5];

libavformat/iamf_writer.c

@@ -42,8 +42,12 @@ static int update_extradata(IAMFCodecConfig *codec_config)
         if (codec_config->extradata_size < 19)
             return AVERROR_INVALIDDATA;
         codec_config->extradata_size -= 8;
-        memmove(codec_config->extradata, codec_config->extradata + 8, codec_config->extradata_size);
-        AV_WB8(codec_config->extradata + 1, 2); // set channels to stereo
+        AV_WB8(codec_config->extradata  + 0, AV_RL8(codec_config->extradata + 8)); // version
+        AV_WB8(codec_config->extradata  + 1, 2); // set channels to stereo
+        AV_WB16(codec_config->extradata + 2, AV_RL16(codec_config->extradata + 10)); // Byte swap pre-skip
+        AV_WB32(codec_config->extradata + 4, AV_RL32(codec_config->extradata + 12)); // Byte swap sample rate
+        AV_WB16(codec_config->extradata + 8, 0); // set Output Gain to 0
+        AV_WB8(codec_config->extradata + 10, AV_RL8(codec_config->extradata + 18)); // Mapping family
         break;
     case AV_CODEC_ID_FLAC: {
         uint8_t buf[13];

tests/ref/fate/iamf-5_1-copy

@@ -1,7 +1,7 @@
-#extradata 0:       19, 0x379c0490
-#extradata 1:       19, 0x379c0490
-#extradata 2:       19, 0x3792048f
-#extradata 3:       19, 0x3792048f
+#extradata 0:       19, 0x3a0e0490
+#extradata 1:       19, 0x3a0e0490
+#extradata 2:       19, 0x3a04048f
+#extradata 3:       19, 0x3a04048f
 #tb 0: 1/48000
 #media_type 0: audio
 #codec_id 0: opus

tests/ref/fate/iamf-5_1-demux

@@ -1,7 +1,7 @@
-#extradata 0:       19, 0x379c0490
-#extradata 1:       19, 0x379c0490
-#extradata 2:       19, 0x3792048f
-#extradata 3:       19, 0x3792048f
+#extradata 0:       19, 0x3a0e0490
+#extradata 1:       19, 0x3a0e0490
+#extradata 2:       19, 0x3a04048f
+#extradata 3:       19, 0x3a04048f
 #tb 0: 1/48000
 #media_type 0: audio
 #codec_id 0: opus