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Fix AC-3 channel count read from wrong nibble in VTS audio attr

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The VTS_AST_ATR byte 1 stores (channels - 1) in the low 3 bits, but we
were reading the high nibble. A normal 2.0 AC-3 track has 0x1 in the low
nibble and 0x0 in the high nibble, so we computed 0+1=1 and mislabeled
every stereo track as mono in the muxed Channels element.

Read the low 3 bits instead, and correct the two audio_attr tests that
had encoded (channels - 1) in the high nibble to match the buggy reader.
This commit is contained in:
Matthew Jackson
2026-06-24 09:39:02 -07:00
parent 45a7b74ab9
commit 2613a81f09
1 changed files with 5 additions and 5 deletions
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src/ifo.rs
+5 -5
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@@ -444,7 +444,7 @@ fn parse_audio_attr(data: &[u8], offset: usize) -> Result<DvdAudioAttr> {
_ => 48000, _ => 48000,
}; };
let channels = ((b1 >> 4) & 0x0F) + 1; // stored as channels minus 1 let channels = (b1 & 0x07) + 1; // (channels - 1) in low 3 bits of byte 1
// Language code: bytes 2-3 as ISO 639 // Language code: bytes 2-3 as ISO 639
let lang_bytes = sub_slice(data, offset + 2, 2)?; let lang_bytes = sub_slice(data, offset + 2, 2)?;
@@ -926,8 +926,8 @@ mod tests {
// AC3 (coding=0), 48kHz (rate=0), 6 channels (stored as 5) // AC3 (coding=0), 48kHz (rate=0), 6 channels (stored as 5)
// b0: bits 7-5=000(AC3), bits 4-3=00(48k) => 0x00 // b0: bits 7-5=000(AC3), bits 4-3=00(48k) => 0x00
data[0] = 0x00; data[0] = 0x00;
// b1: bits 7-4=0101 (channels-1=5) => 0x50 // b1: bits 2-0=101 (channels-1=5) => 0x05
data[1] = 0x50; data[1] = 0x05;
// language "en" // language "en"
data[2] = b'e'; data[2] = b'e';
data[3] = b'n'; data[3] = b'n';
@@ -993,8 +993,8 @@ mod tests {
// DTS (coding=6), 96kHz (rate=1), 2 channels (stored as 1) // DTS (coding=6), 96kHz (rate=1), 2 channels (stored as 1)
// b0: bits 7-5=110(DTS), bits 4-3=01(96k) => 0b110_01_000 = 0xC8 // b0: bits 7-5=110(DTS), bits 4-3=01(96k) => 0b110_01_000 = 0xC8
data[0] = 0xC8; data[0] = 0xC8;
// b1: bits 7-4=0001 (channels-1=1) => 0x10 // b1: bits 2-0=001 (channels-1=1) => 0x01
data[1] = 0x10; data[1] = 0x01;
data[2] = b'f'; data[2] = b'f';
data[3] = b'r'; data[3] = b'r';