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Avoid premature saturation in H264 type 1 POC

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Dylan M. Taylor committed 2026-11-13 07:11:12 +00:00
1 parent 80731087bf
commit 56a1f2b7c4
1 file changed
+19 -9
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crates/video/src/h264/decode/slice.rs
+19 -9
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@@ -475,26 +475,27 @@ impl PocState {
}
1 => {
let frame_num_offset = self.frame_num_offset(sh.idr, sh.frame_num, sps);
let n = sps.offset_for_ref_frame.len() as i32;
let mut abs_frame_num = if n != 0 { frame_num_offset.saturating_add(sh.frame_num as i32) } else { 0 };
let n = sps.offset_for_ref_frame.len() as i64;
let mut abs_frame_num = if n != 0 { i64::from(frame_num_offset) + i64::from(sh.frame_num) } else { 0 };
if sh.nal_ref_idc == 0 && abs_frame_num > 0 {
abs_frame_num -= 1;
}
let mut expected = 0i32;
let mut expected = 0i64;
if abs_frame_num > 0 {
let cycle_cnt = (abs_frame_num - 1) / n;
let in_cycle = (abs_frame_num - 1) % n;
let delta_cycle = sps.offset_for_ref_frame.iter().fold(0i32, |a, &o| a.saturating_add(o));
expected = cycle_cnt.saturating_mul(delta_cycle);
let delta_cycle = sps.offset_for_ref_frame.iter().map(|&o| i64::from(o)).sum::<i64>();
expected = cycle_cnt * delta_cycle;
for &o in &sps.offset_for_ref_frame[..=in_cycle as usize] {
expected = expected.saturating_add(o);
expected += i64::from(o);
}
}
if sh.nal_ref_idc == 0 {
expected = expected.saturating_add(sps.offset_for_non_ref_pic);
expected += i64::from(sps.offset_for_non_ref_pic);
}
let top = expected.saturating_add(sh.delta_pic_order_cnt[0]);
let bottom = top.saturating_add(sps.offset_for_top_to_bottom_field).saturating_add(sh.delta_pic_order_cnt[1]);
let top = (expected + i64::from(sh.delta_pic_order_cnt[0])).clamp(i64::from(i32::MIN), i64::from(i32::MAX)) as i32;
let bottom = (i64::from(top) + i64::from(sps.offset_for_top_to_bottom_field) + i64::from(sh.delta_pic_order_cnt[1]))
.clamp(i64::from(i32::MIN), i64::from(i32::MAX)) as i32;
Poc { top, bottom, msb: 0, frame_num_offset }
}
_ => {
@@ -662,4 +663,13 @@ mod poc_tests {
let _ = poc.frame();
state.update(&sh, &poc);
}
#[test]
fn poc_type1_cancellation_happens_before_clamping() {
let sps = sps(1);
let sh = header(0, 0, 0, [-i32::MAX, 0], 1);
let state = PocState { prev_frame_num_offset: 2, ..PocState::default() };
let poc = state.compute(&sh, &sps);
assert_eq!(poc.top, i32::MAX);
}
}