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video: saturate extreme H.264 picture order values

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Dylan M. Taylor committed 2026-11-13 00:44:21 +00:00
1 parent 409b0036f8
commit 6fa8323991
1 file changed
+25 -17
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crates/video/src/h264/decode/slice.rs
+25 -17
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@@ -462,21 +462,21 @@ impl PocState {
let (prev_msb, prev_lsb) = if sh.idr { (0, 0) } else { (self.prev_ref_msb, self.prev_ref_lsb) };
let max_lsb = 1i32 << sps.log2_max_poc_lsb;
let lsb = sh.pic_order_cnt_lsb as i32;
let msb = if lsb < prev_lsb && prev_lsb.wrapping_sub(lsb) >= max_lsb / 2 {
prev_msb.wrapping_add(max_lsb)
} else if lsb > prev_lsb && lsb.wrapping_sub(prev_lsb) > max_lsb / 2 {
prev_msb.wrapping_sub(max_lsb)
let msb = if lsb < prev_lsb && prev_lsb.saturating_sub(lsb) >= max_lsb / 2 {
prev_msb.saturating_add(max_lsb)
} else if lsb > prev_lsb && lsb.saturating_sub(prev_lsb) > max_lsb / 2 {
prev_msb.saturating_sub(max_lsb)
} else {
prev_msb
};
let top = msb.wrapping_add(lsb);
let bottom = top.wrapping_add(sh.delta_pic_order_cnt_bottom);
let top = msb.saturating_add(lsb);
let bottom = top.saturating_add(sh.delta_pic_order_cnt_bottom);
Poc { top, bottom, msb, frame_num_offset: 0 }
}
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.wrapping_add(sh.frame_num as i32) } else { 0 };
let mut abs_frame_num = if n != 0 { frame_num_offset.saturating_add(sh.frame_num as i32) } else { 0 };
if sh.nal_ref_idc == 0 && abs_frame_num > 0 {
abs_frame_num -= 1;
}
@@ -484,17 +484,17 @@ impl PocState {
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.wrapping_add(o));
expected = cycle_cnt.wrapping_mul(delta_cycle);
let delta_cycle = sps.offset_for_ref_frame.iter().fold(0i32, |a, &o| a.saturating_add(o));
expected = cycle_cnt.saturating_mul(delta_cycle);
for &o in &sps.offset_for_ref_frame[..=in_cycle as usize] {
expected = expected.wrapping_add(o);
expected = expected.saturating_add(o);
}
}
if sh.nal_ref_idc == 0 {
expected = expected.wrapping_add(sps.offset_for_non_ref_pic);
expected = expected.saturating_add(sps.offset_for_non_ref_pic);
}
let top = expected.wrapping_add(sh.delta_pic_order_cnt[0]);
let bottom = top.wrapping_add(sps.offset_for_top_to_bottom_field).wrapping_add(sh.delta_pic_order_cnt[1]);
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]);
Poc { top, bottom, msb: 0, frame_num_offset }
}
_ => {
@@ -502,9 +502,9 @@ impl PocState {
let temp = if sh.idr {
0
} else if sh.nal_ref_idc == 0 {
2i32.wrapping_mul(frame_num_offset.wrapping_add(sh.frame_num as i32)).wrapping_sub(1)
2i32.saturating_mul(frame_num_offset.saturating_add(sh.frame_num as i32)).saturating_sub(1)
} else {
2i32.wrapping_mul(frame_num_offset.wrapping_add(sh.frame_num as i32))
2i32.saturating_mul(frame_num_offset.saturating_add(sh.frame_num as i32))
};
Poc { top: temp, bottom: temp, msb: 0, frame_num_offset }
}
@@ -515,7 +515,7 @@ impl PocState {
if idr {
0
} else if self.prev_frame_num > frame_num {
self.prev_frame_num_offset.wrapping_add(sps.max_frame_num() as i32)
self.prev_frame_num_offset.saturating_add(sps.max_frame_num() as i32)
} else {
self.prev_frame_num_offset
}
@@ -528,7 +528,7 @@ impl PocState {
if sh.nal_ref_idc != 0 {
if mmco5 {
self.prev_ref_msb = 0;
self.prev_ref_lsb = poc.top.wrapping_sub(poc.frame());
self.prev_ref_lsb = poc.top.saturating_sub(poc.frame());
} else {
self.prev_ref_msb = poc.msb;
self.prev_ref_lsb = sh.pic_order_cnt_lsb as i32;
@@ -624,6 +624,14 @@ mod poc_tests {
}
}
#[test]
fn extreme_bottom_delta_saturates_instead_of_reversing_picture_order() {
let sps = sps(0);
let sh = header(0, 1, i32::MAX, [0, 0], 1);
let poc = PocState::default().compute(&sh, &sps);
assert_eq!((poc.top, poc.bottom), (1, i32::MAX));
}
/// Offsets and deltas are se(v) values that a stream may set anywhere in the i32 range.
#[test]
fn poc_does_not_overflow_on_extreme_deltas() {