Parse AVI stream numbers as decimal (#3603)

* Parse AVI stream numbers as decimal

Found while testing crates/avi/src/lib.rs:158

Co-Authored-By: GPT-6-Luna <noreply@openai.com>

* fix: support decimal and hexadecimal AVI stream IDs

Co-Authored-By: GPT-6-Luna <noreply@openai.com>

* avi: two decimal digits or a hex letter, never a sign, in a stream id

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: GPT-6-Luna <noreply@openai.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/avi/src/lib.rs

@@ -156,8 +156,12 @@ pub struct Stream {
 impl Stream {
     /// Stream index of a `movi` chunk id (`00dc`, `01wb`…): its first two characters.
     fn number(id: &[u8; 4]) -> Option<usize> {
-        let d = |b: u8| (b as char).to_digit(16).map(|v| v as usize);
-        Some(d(id[0])? * 16 + d(id[1])?)
+        // ffmpeg-style writers number streams in decimal ("10dc" = 10), Video for Windows in hex
+        // ("0adc" = 10): a hex letter means hex, two decimal digits mean decimal
+        let [a, b, ..] = *id;
+        let radix = if [a, b].iter().any(|c| matches!(c, b'a'..=b'f' | b'A'..=b'F')) { 16 } else { 10 };
+        let d = |c: u8| (c as char).to_digit(radix).map(|v| v as usize);
+        Some(d(a)? * radix as usize + d(b)?)
     }
 }
 

crates/avi/src/tests.rs

@@ -1,5 +1,17 @@
 use super::*;
 
+#[test]
+fn stream_number_supports_decimal_and_hex_ids() {
+    assert_eq!(Stream::number(b"10dc"), Some(10));
+    assert_eq!(Stream::number(b"0adc"), Some(10));
+    assert_eq!(Stream::number(b"00dc"), Some(0));
+    assert_eq!(Stream::number(b"09wb"), Some(9));
+    assert_eq!(Stream::number(b"0Fdc"), Some(15));
+    // `from_str_radix` would take a sign; a chunk id never has one
+    assert_eq!(Stream::number(b"+1dc"), None);
+    assert_eq!(Stream::number(b"ixdc"), None);
+}
+
 fn chunk(id: &[u8; 4], data: &[u8]) -> Vec<u8> {
     let mut v = id.to_vec();
     v.extend_from_slice(&(data.len() as u32).to_le_bytes());