craft-audio: review fixes, round 6 (#443)

Two tests from round 1 failed on ffmpeg before 9, including CI's 8.0. Neither was
a decoding fault:
- ffmpeg 9 ends an MP4 with no edit list at its sample durations and earlier
  versions present the whole last packet, so the length is checked against the
  file's known duration, not ffmpeg's decode.
- The order ffmpeg gives channels with -aac_pce differs by version, so each decoded
  channel must match a different one of ffmpeg's, whatever the order.

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

crates/audio/tests/codecs/routing_oracle.rs

@@ -469,14 +469,28 @@ fn adts_with_a_program_config_element_decodes() {
     assert_eq!((info.container, info.codec, buf.channels.len()), (c.container, c.codec, c.channels));
     assert_eq!(info.layout, c.layout);
     assert_eq!(buf.frames(), reference(&ff, &path).len() / c.channels);
-    // Decoded order (C, L, R, surrounds, LFE) against ffmpeg's (L, R, C, LFE, surrounds).
-    let wav: Vec<Vec<f32>> = [1, 2, 0, 5, 3, 4].iter().map(|&i| buf.channels[i].clone()).collect();
-    let s = snr(&wav, &reference(&ff, &path));
-    assert!(s >= c.min_snr, "SNR {s:.1} dB");
+    // A program config's channels come in its own order, and which order ffmpeg writes differs by
+    // version: each of ours must match a different one of ffmpeg's.
+    let refr = reference(&ff, &path);
+    let mut matched = Vec::new();
+    for plane in &buf.channels {
+        let (best, s) = (0..c.channels)
+            .map(|r| {
+                let other: Vec<f32> = refr.iter().skip(r).step_by(c.channels).copied().collect();
+                (r, snr(std::slice::from_ref(plane), &other))
+            })
+            .max_by(|a, b| a.1.total_cmp(&b.1))
+            .unwrap();
+        assert!(s >= c.min_snr, "channel {} matches ffmpeg's {best} at only {s:.1} dB", matched.len());
+        matched.push(best);
+    }
+    matched.sort_unstable();
+    assert_eq!(matched, (0..c.channels).collect::<Vec<_>>());
 }
 
 /// `probe` and `decode` agree on an MP4's length when no single edit gives it: the samples'
-/// durations end the track, as they do for ffmpeg.
+/// durations end the track. ffmpeg 9 does the same, but earlier versions present the whole last
+/// packet, so the length is not compared with its decode.
 #[test]
 fn mp4_without_an_edit_list_ends_with_its_sample_durations() {
     let ff = require_ffmpeg!();
@@ -498,7 +512,8 @@ fn mp4_without_an_edit_list_ends_with_its_sample_durations() {
     let (info, buf) = decode(&bytes, None).unwrap();
     assert_eq!(probe(&bytes, None).unwrap().frames, buf.frames() as u64);
     assert_eq!(info.frames, buf.frames() as u64);
-    assert_eq!(buf.frames(), reference(&ff, &path).len() / c.channels);
+    // 5 s, and 1024 frames of priming with no edit list to skip them.
+    assert_eq!(buf.frames(), 5 * 44_100 + 1024);
 }
 
 /// The big-endian `u32` at each of `offsets` after the first `box_name` in `file`, changed by `edit`.