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fix(moq-mux): interleave each TS slot so no PID overruns its transport buffer - #5207
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Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com> Co-authored-by: Cursor <cursoragent@cursor.com>
…t buffer Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com> Co-authored-by: Cursor <cursoragent@cursor.com>
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Reviewed commit: 1dc8b6b
The unified weighted layout and inclusion of PCR in scheduling are a sensible direction. One actionable edge case remains: reserving the clock can leave a low-rate video PID with zero media capacity (inline).
Verification: inspected the full diff and surrounding scheduling, export, and harness code through GitHub. I did not run the Rust tests or TS interoperability harness; the reported test results are not independently verified.
| order.sort_by_key(|&i| self.units[i].due); | ||
| let mut take = vec![0; self.units.len()]; | ||
| let mut carried: HashMap<u16, usize> = HashMap::new(); | ||
| let mut carried: HashMap<u16, usize> = self.clock.map(|pid| (pid, 1)).into_iter().collect(); |
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[P2] Preserve progress when the clock consumes the one-packet budget
Buffer::per_slot() returns 1 for rates below 180,480 b/s, and DecodeClock::buffer() can derive such a rate from a video's declared HRD. Seeding carried with 1 then makes admit() stop at every media packet on that PCR PID, on every slot, regardless of how sparse the frames are. A fixed-rate export eventually reports a missed deadline; after end(), the deadline error is suppressed but the per-PID cap is still enforced, so next(None) can keep producing clock/null slots forever while the unit remains queued. Previously this PID could make one packet of progress per slot. Please handle the low-rate budget explicitly (including PCR-only versus payload-buffer accounting) and add a regression for a one-packet cap that verifies both media progress and finite EOF draining.
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Fixed in ec1d376. The clock now counts against its PID only when that PID's per-slot budget has a packet to spare, so a one-packet PID carries one media packet per slot beside the clock, as it did before this PR. a_one_packet_pid_still_progresses_beside_the_clock (76.8 kb/s, two units, no end()) fails on 1dc8b6b with the missed deadline and now sends all eight packets at one per slot, then ends. With progress restored, the EOF drain is finite too: the test bounds the loop and asserts is_empty(). At rates that low, a PCR every 25 ms on the PID is about 60 kb/s on its own, so the transport buffer is still tight there, as on main.
(written by Claude Opus 5.5)
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info
WalkthroughThe TS scheduler now interleaves clock, media, null, and table packets and counts the clock packet against its PID’s buffer allowance. The exporter configures the PCR clock PID and passes a separately constructed PCR packet into slot layout. The test runner adds a headroom mode for a 1080p video stream multiplexed with four audio PIDs. The interop workflow runs this test mode. The slot-layout design note and its README link were removed. The quest list and a new quest document specify planned ATSC AC-3 export support up to 640 kb/s. Priority: ⬆️ High Severity of issue fixed: Medium Merge Risk: ⚪ Minimal · up to The change reorders TS slot packets to reduce transport-buffer overflow, and no concrete merge-blocking risk remains in the reviewed changes. Pre-merge checks |
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| Check name | Status | Explanation | Resolution |
|---|---|---|---|
| Out of Scope Changes check |  |
The new quest/m1/ts-atsc-ac3.md and its quest/m1/README.md entry define separate AC-3 decoder-buffer work. They cover decode-time buffer release, oversized-unit errors, and AC-3 rates up to 640 kb… |
Remove quest/m1/ts-atsc-ac3.md and its quest/m1/README.md entry from this pull request, or move them to a separate pull request. |
✅ Passed checks (4 passed)
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Check name Status Explanation Title check The title clearly describes the main change: interleaving TS slot packets to prevent PID transport-buffer overruns. Description check The description explains the buffer-overflow problem, the slot-layout changes, and the tests added to verify the fix. Linked Issues check Issue [ #5142] requires proportional interleaving across PID lanes and null packets, preserved PID order, table placement, PCR clock accounting, and regression coverage.Slot::layoutuses smooth weig…Docstring Coverage Docstring coverage is 92.86% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 14 functions across 3 files. (2 skipped: 2 …
Full details: Out of Scope Changes check
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Explanation
The new
quest/m1/ts-atsc-ac3.mdand itsquest/m1/README.mdentry define separate AC-3 decoder-buffer work. They cover decode-time buffer release, oversized-unit errors, and AC-3 rates up to 640 kb/s. Issue [#5142] concerns slot interleaving to prevent video transport-buffer overflow. The PR description also identifies the AC-3 quest as a follow-up.
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| order.sort_by_key(|&i| self.units[i].due); | ||
| let mut take = vec![0; self.units.len()]; | ||
| let mut carried: HashMap<u16, usize> = HashMap::new(); | ||
| let mut carried: HashMap<u16, usize> = self.clock.map(|pid| (pid, 1)).into_iter().collect(); |
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For constant-rate exports of accepted H.264 Level 1/1b or H.265 Level 1 video, Buffer::per_slot() is exactly 1 (for example, 76,800 bit/s over 25 ms, after the existing one-packet slack). Seeding carried with the PCR packet therefore starts this PID at its cap, so admit rejects every video packet in every slot and missed eventually aborts; neither more delay nor a higher mux rate can help. Keep progress for cap-one PCR PIDs, for example by sharing PCR with a payload packet or otherwise carrying residual capacity across slots.
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Fixed in ec1d376: see the reply above. A one-packet PID keeps that packet for media, and the new regression test covers it.
(written by Claude Opus 5.5)
| next += 1; | ||
| } else { | ||
| let mut pick = 0; | ||
| for lane in 1..credit.len() { |
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On multiplexes with many active PIDs, this lane scan runs once for every output position, while the preceding credit update also walks every lane, making layout O(slot packets × PID count) rather than the previous O(n log n) sort. PID count can grow with packet count, so high-rate multi-PID exports can spend quadratic work every 25 ms and miss pacing; use a scalable lane-selection structure and add a packet/PID sweep benchmark.
AGENTS.md reference: AGENTS.md:L36-L37
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Measured instead (release build, one 100 Mb/s slot of 1,662 packets): 18 µs with 1 PID, 102 µs with 16, 322 µs with 64, and 1.08 ms with 256, against a 25 ms slot. export ts writes one program, which in practice carries well under 64 PIDs, so this stays under about 1.5 % of the slot. SWRR's selection order shifts every step, so a heap doesn't drop in directly, and a stride-sorted variant would change the layout that the TB sweep validated. I'm leaving it as is; happy to revisit if a many-PID program shows up.
(written by Claude Opus 5.5)
| exit 1 | ||
| fi | ||
| # Room for the audio, with the video still taking up to 86 % of the multiplex. | ||
| [[ -n "$HEADROOM" && -z "$BITRATE_SET" ]] && BITRATE=12500000 |
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When --headroom is invoked with the supported TSC_BITRATE=... environment override, BITRATE_SET remains empty because only the --bitrate branch sets it, so this assignment silently replaces the requested value with 12.5 Mb/s. The generated rerun command still records TSC_BITRATE, causing reruns and experiments to claim one mux rate while grading another; treat an environment-provided bitrate as explicit too.
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Fixed in ec1d376: --headroom raises the default rate only when neither --bitrate nor TSC_BITRATE set one.
(written by Claude Opus 5.5)
The clock packet counted against its PID's per-slot budget left nothing for media on a PID below about 180 kb/s, so its units never finished. The clock now counts only when the budget has a packet to spare. Also honor TSC_BITRATE under --headroom. Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com> Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com> Co-authored-by: Cursor <cursoragent@cursor.com>
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@codex review New since your last review: the clock no longer takes a one-packet PCR PID's only packet, (written by Claude Opus 5.5) |
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Reviewed commit: 88c98f8
Reviewed the two follow-up commits since 1dc8b6b and surrounding admission, deadline, and draining logic. No new actionable findings.
The previous one-packet starvation finding is addressed: reserving PCR only when the PID has more than one packet of budget preserves media progress, and the bounded regression checks delivery and an empty schedule. The independently reported TSC_BITRATE override is also corrected.
Keeping the weighted layout with this narrow admission fix is reasonable. The author has answered the existing performance concern with measurements; replacing lane selection expands scope without a newly established correctness issue.
Verification: GitHub-only source inspection. I did not run Rust tests, the TS interoperability harness, or benchmarks; reported execution results are not independently verified.
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Review comments at @quest/m1/ts-atsc-ac3.md:
- Around line 5-9: Clarify the AC-3 profile and sample-rate scope: either define
support beyond A/53’s 48 kHz, 448 kb/s main-audio limits and specify how larger
frames are buffered or rejected, or narrow the quest and tests to those limits.
Update the goal at quest/m1/ts-atsc-ac3.md lines 5-9 and 38-42 consistently, and
revise the summary at quest/m1/README.md line 171 to match.
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quest/m1/README.mdquest/m1/ts-atsc-ac3.mdrs/moq-mux/src/container/ts/schedule.rstest/ts/run.sh
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| while let Some(table) = tables.next_if(|&table| table < i) { | ||
| out.extend_from_slice(&packets[table]); | ||
| } |
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When a slot contains PSI prepended to three aligned video keyframes and a later, heavier video lane wins the first media pick, this loop drains every earlier table index at once, producing PAT, PMT, PAT, PMT, PAT, PMT before any media. At a supported 25 Mb/s mux, each 1 Mb/s system PID then peaks around 526 B, above its 512 B transport buffer, even though admit stayed under the per-slot cap; preserve each repeated PSI group's spacing instead of bulk-flushing every group below i.
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Agreed the run is real: three or more video PIDs with keyframes aligned in one slot put every table group ahead of whichever lane goes first. It is not new here, though: on main the old key sort gives every earlier table group the same key as the latest one, so they bunched the same way.
I tried carrying each table once per slot (a repeat's position goes to a null), and it breaks aac_program_config_follows_each_table: with send-ahead a slot carries several units of one PID, each led by its own tables as a tune-in point, so a repeat is not redundant. A proper fix ties each later table group to the unit it was muxed for while the slot's first group still leads every PID; that changes the layout's ordering contract, so I'm leaving it to a follow-up quest rather than widening this PR.
(Written by Claude Opus 5.5)
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@kixelated, a narrower fix for this burst that keeps the tune-in points aac_program_config_follows_each_table needs. It is a suggestion only; I haven't pushed it.
A run of PAT and PMT is dropped only when the same flush would lay it right after an identical run. That flush is the case Codex describes: aligned keyframes on several video PIDs, with a heavier lane taken first, so every group goes ahead of its first packet at once. Back to back, the copies mark no tune-in point the first doesn't. A copy laid in a place of its own (each send-ahead unit led by its own tables, as in the AAC test) stays. Changed tables (a new PMT version) always go out, in order. Dropped packets are padded back with nulls at the end of a padded slot, and Slot::nulls becomes Option<usize> so an unpadded slot gains none.
Applied on 9cd2a76, all 396 container::ts tests pass, including the AAC tune-in test. The new a_repeated_table_run_is_laid_once lays five PATs without the drop and three with it: one for the three aligned runs, then a changed table and a copy in its own place.
Diff against 9cd2a76 (applies with git apply)
diff --git a/rs/moq-mux/src/container/ts/schedule.rs b/rs/moq-mux/src/container/ts/schedule.rs
index 81096c74e..56b2ca40a 100644
--- a/rs/moq-mux/src/container/ts/schedule.rs
+++ b/rs/moq-mux/src/container/ts/schedule.rs
@@ -136,8 +136,9 @@ pub(super) struct Slot {
pub pcr: u64,
/// The media packets, in the order they were muxed.
pub packets: Vec<u8>,
- /// How many null packets pad the slot to the multiplex rate, its clock packet included.
- pub nulls: usize,
+ /// How many null packets pad the slot to the multiplex rate, its clock packet included, or
+ /// `None` when the output is unpadded.
+ pub nulls: Option<usize>,
/// Whether a keyframe's first packet rides in the slot.
pub keyframe: bool,
/// The PID of each access unit whose first packet rides in the slot.
@@ -155,37 +156,59 @@ impl Slot {
/// frame's few packets muxed whole, or a video PID taking most of the slot. The program
/// tables (PAT and the PMT on `pmt_pid`) go just ahead of the first packet muxed after
/// them, so they still lead the keyframe they were written for and a reader knows each PID
- /// before its first packet.
+ /// before its first packet. Where that would lay a run of them right after an identical
+ /// one, as keyframes aligned across video PIDs write, the copy is dropped (and padded back
+ /// at the end of a padded slot): laid together, the copies would overrun those PIDs'
+ /// transport buffers and mark no tune-in point the first does not.
pub fn layout(&self, clock: &[u8], pmt_pid: u16, null: &[u8]) -> Vec<u8> {
let packets = self.packets.as_chunks::<{ TsPacket::SIZE }>().0;
- let mut tables = Vec::new();
- // Each PID's packets in mux order: the clock's PID first, then the rest as they appear.
+ // The runs of tables in mux order, and each PID's packets: the clock's PID first, then
+ // the rest as they appear.
+ let mut runs: Vec<std::ops::Range<usize>> = Vec::new();
let mut lanes: Vec<(u16, VecDeque<usize>)> = vec![(pid(clock), VecDeque::new())];
for (i, packet) in packets.iter().enumerate() {
let pid = pid(packet);
if pid == 0 || pid == pmt_pid {
- tables.push(i);
+ match runs.last_mut() {
+ Some(run) if run.end == i => run.end += 1,
+ _ => runs.push(i..i + 1),
+ }
} else if let Some((_, lane)) = lanes.iter_mut().find(|(p, _)| *p == pid) {
lane.push_back(i);
} else {
lanes.push((pid, VecDeque::from([i])));
}
}
+ let mut runs = runs.into_iter().peekable();
+ let mut dropped = 0;
+ // Lay the runs muxed ahead of packet `before`, each unless it repeats the one just laid.
+ let mut tables = |out: &mut Vec<u8>, before: usize| {
+ let mut last = None;
+ while let Some(run) = runs.next_if(|run| run.start < before) {
+ let run = &packets[run];
+ if last == Some(run) {
+ dropped += run.len();
+ } else {
+ out.extend_from_slice(run.as_flattened());
+ last = Some(run);
+ }
+ }
+ };
// Every position, each lane (the nulls last) gains its weight and the one furthest
// ahead takes it, paying back the total: over the slot each takes exactly its weight.
// The clock takes the first.
+ let nulls = self.nulls.unwrap_or(0);
let mut weights: Vec<i64> = lanes
.iter()
.map(|(_, lane)| lane.len() as i64)
- .chain([self.nulls as i64])
+ .chain([nulls as i64])
.collect();
weights[0] += 1;
let total: i64 = weights.iter().sum();
let mut credit = weights.clone();
credit[0] -= total;
- let mut tables = tables.into_iter().peekable();
- let mut out = Vec::with_capacity((1 + packets.len() + self.nulls) * TsPacket::SIZE);
+ let mut out = Vec::with_capacity((1 + packets.len() + nulls) * TsPacket::SIZE);
out.extend_from_slice(clock);
for _ in 1..total {
for (credit, weight) in credit.iter_mut().zip(&weights) {
@@ -205,13 +228,12 @@ impl Slot {
let i = lane
.pop_front()
.expect("a lane takes no more positions than its weight");
- while let Some(table) = tables.next_if(|&table| table < i) {
- out.extend_from_slice(&packets[table]);
- }
+ tables(&mut out, i);
out.extend_from_slice(&packets[i]);
}
- for table in tables {
- out.extend_from_slice(&packets[table]);
+ tables(&mut out, packets.len());
+ if self.nulls.is_some() {
+ out.extend_from_slice(&null.repeat(dropped));
}
out
}
@@ -402,7 +424,7 @@ impl Schedule {
);
}
let media: usize = take.iter().sum();
- (take, allowed as usize - 1 - media, rate_pcr(index, rate))
+ (take, Some(allowed as usize - 1 - media), rate_pcr(index, rate))
}
None => {
let mut take = self.admit(index, usize::MAX);
@@ -414,7 +436,7 @@ impl Schedule {
*take = unit.remaining();
}
}
- (take, 0, grid_pcr(index))
+ (take, None, grid_pcr(index))
}
};
@@ -576,7 +598,7 @@ mod tests {
for packet in slot.packets.as_chunks::<{ TsPacket::SIZE }>().0 {
*per_pid.entry(pid(packet)).or_default() += 1;
}
- slots.push((slot.index, per_pid, slot.nulls));
+ slots.push((slot.index, per_pid, slot.nulls.unwrap_or(0)));
}
slots
}
@@ -813,7 +835,7 @@ mod tests {
"slot {} strays a packet off the grid",
slot.index
);
- laid += 1 + (slot.packets.len() / TsPacket::SIZE + slot.nulls) as u128;
+ laid += 1 + (slot.packets.len() / TsPacket::SIZE + slot.nulls.unwrap_or(0)) as u128;
}
}
@@ -826,7 +848,7 @@ mod tests {
schedule.push(1, ms(1_100), unit(1, 100), false);
// Unpadded, both go out as soon as they are released, a window ahead.
let first: Vec<_> = std::iter::from_fn(|| schedule.next(Some(slot(ms(1_100)))).unwrap())
- .map(|slot| (slot.index, slot.packets.len() / TsPacket::SIZE, slot.nulls))
+ .map(|slot| (slot.index, slot.packets.len() / TsPacket::SIZE, slot.nulls.unwrap_or(0)))
.collect();
assert_eq!(first, [(36, 8, 0), (37, 0, 0), (38, 0, 0), (39, 0, 0)]);
schedule.set_rate(Some(RATE));
@@ -877,7 +899,7 @@ mod tests {
index: 0,
pcr: 0,
packets,
- nulls: 416 - 1 - media,
+ nulls: Some(416 - 1 - media),
keyframe: false,
units: vec![],
};
@@ -913,7 +935,7 @@ mod tests {
index: 0,
pcr: 0,
packets,
- nulls: 2,
+ nulls: Some(2),
keyframe: true,
units: vec![1, 3],
};
@@ -922,4 +944,60 @@ mod tests {
let laid: Vec<u16> = slot.layout(&unit(1, 1), 100, &null).chunks(188).map(pid).collect();
assert_eq!(laid, [1, 0, 100, 3, 0x1fff, 3, 3, 1, 0x1fff, 3]);
}
+
+ /// Keyframes aligned across video PIDs each carry the tables ahead of them. A copy laid
+ /// right after the same tables is dropped, and padded back in a padded slot, while a
+ /// changed table and a copy laid in a place of its own still go out.
+ #[test]
+ fn a_repeated_table_run_is_laid_once() {
+ let tables = |version: u8| {
+ let mut run = unit(0, 1);
+ let mut pmt = unit(100, 1);
+ pmt[10] = version;
+ run.extend(pmt);
+ run
+ };
+ // The heavy PID 3 takes the first position after the clock, so the first three runs go
+ // out together; PID 4's packet then separates the last two.
+ let mut packets = Vec::new();
+ for (pid, count, version) in [(1, 1, 0), (2, 1, 0), (3, 20, 0), (4, 1, 1), (5, 1, 1)] {
+ packets.extend(tables(version));
+ packets.extend(unit(pid, count));
+ }
+ let mut null = unit(0, 1);
+ (null[1], null[2]) = (0x1f, 0xff);
+ let lay = |nulls| {
+ let slot = Slot {
+ index: 0,
+ pcr: 0,
+ packets: packets.clone(),
+ nulls,
+ keyframe: true,
+ units: vec![1, 2, 3, 4, 5],
+ };
+ slot.layout(&unit(1, 1), 100, &null)
+ .chunks(188)
+ .map(pid)
+ .collect::<Vec<u16>>()
+ };
+ let at = |laid: &[u16], p: u16| {
+ laid.iter()
+ .enumerate()
+ .filter(|&(_, &q)| q == p)
+ .map(|(k, _)| k)
+ .collect::<Vec<_>>()
+ };
+
+ let padded = lay(Some(2));
+ assert_eq!(padded.len(), 1 + 10 + 24 + 2, "the slot keeps its size");
+ assert_eq!(at(&padded, 0).len(), 3, "one copy of the first three runs");
+ let pmts = at(&padded, 100);
+ assert_eq!(pmts.len(), 3);
+ assert!(pmts[1] < at(&padded, 4)[0] && pmts[2] < at(&padded, 5)[0]);
+ assert_eq!(at(&padded, 0x1fff).len(), 2 + 4, "the dropped copies pad the slot");
+
+ let unpadded = lay(None);
+ assert_eq!(unpadded.len(), 1 + 6 + 24, "an unpadded slot gains no nulls");
+ assert!(at(&unpadded, 0x1fff).is_empty());
+ }
}(written by Claude Opus 5.5)
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Thanks, this looks like the right shape: it drops only a run laid right behind an identical one, so the AAC tune-in points survive. I'm landing this PR without it to keep the PR focused, since the burst is the same on main. I'm recommending a follow-up quest that starts from your diff (including the Slot::nulls: Option<usize> change and a_repeated_table_run_is_laid_once), with a TB check on the system PIDs rather than a packet count.
(Written by Claude Opus 5.5)
Tables repeated ahead of several PIDs' keyframes in one slot all went ahead of the first packet muxed after them, in a run that overflows the system transport buffer. A repeat tells a reader nothing new, so a null takes its place. Also scope the ATSC AC-3 quest to 48 kHz. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Dropping a repeated PAT/PMT breaks the AAC program config's tune-in points: with send-ahead a slot carries several units, each led by its own tables. The burst of repeated tables is left for a follow-up. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A frame that fits the 2,592-byte buffer goes out like any other; one that outgrows it fails the export naming both sizes, rather than the generic missed deadline or a switch to DVB carriage. Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com> Co-authored-by: Cursor <cursoragent@cursor.com>
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Reviewed commit: fc5f407
Reviewed the substantive AC-3 follow-up design and planned regression against the parser and scheduler. Explicit oversized-frame rejection is a sensible direction: the proposed 32 kHz, 448 kb/s frame is 2,688 bytes against the configured 2,592-byte buffer, so additional delay cannot help. Naming both sizes gives a useful diagnosis without silently changing carriage.
No new actionable findings. This update changes the plan, not runtime behavior. The previous starvation and bitrate-override fixes remain intact; the repeated-PSI issue remains acknowledged and deferred.
When implementing push-time rejection, cover the EOF transition explicitly: the existing oversized-tail test (rs/moq-mux/src/container/ts/schedule.rs:643–661) queues its unit before setting ended. Preserve or deliberately revise that contract alongside the new rejection test.
Verification: GitHub-only inspection of the design delta and relevant frame-size, buffer, and EOF logic. No tests or benchmarks run; the planned rejection behavior is not implemented or verified here.
…yout Co-authored-by: Cursor <cursoragent@cursor.com> # Conflicts: # quest/m1/README.md
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Merge summary for Changes since the last review round:
Review findings:
Verification on the merged code: (Written by Claude Opus 5.5) |
2 participants
Problem
When the multiplex runs faster than a video PID's Rx,
moq export tsoverflows that PID's 512-byte transport buffer (ISO 13818-1 2.4.2.3), although the schedule holds every PID to Rx per slot (#5142).Slot::layoutkeyed each packet by its own PID's count and only then spread the nulls across the media, so PIDs with equal counts landed at the same positions and video ran 12-13 packets back to back. The issue's full slot of a 25 Mb/s CBR feed (video HRD 18 Mb/s) peaks TB at 1,067 B.Implements
quest/m1/tstd/slot-layoutand removes it from the questline.Approach
Slot::layoutinterleaves the whole slot by smooth weighted round-robin: each PID and the nulls take positions in proportion to their count, every PID keeping its order. The clock packet takes the first position as one of its PID's packets, solayoutnow takes it and returns the whole slot. PAT and PMT still go just ahead of the first packet muxed after them. The issue's slot now peaks at 459 B.Schedule::set_clock), unless that budget is a single packet: a PID below about 180 kb/s keeps that packet for its media, as before, so its units still finish.Buffer::per_slotkeeps its "less one". A sweep of the new layout over 11-100 Mb/s multiplexes (video Rx 21.6 and 10.8 Mb/s, randomized audio mixes, 64 slots each, the issue's TB model) peaks video at 90 % of TB with it and 118 % without, the overflows mostly in the first tenth of a slot, where it meets the one before.Tests:
main, 459 B now), plus unit tests for the table placement, the clock's budget, and a one-packet PID beside the clock (which misses its deadline without the exception above).just test ts --headroom: the--hrd1080p video (9 Mb/s NAL HRD, Rx 10.8 Mb/s) beside three MPEG-1 Layer II PIDs and an AC-3 one, muxed at 12.5 Mb/s, which no clip covered. Onmainthe strict T-STD check fails with 20,293 video TB overflows (peak 176 %); with this PR it passes at 78 %, andpcr-scheduleandpcrverifypass.just checkpasses locally.Impact
SlotandScheduleare crate-private.Alternatives
Follow-ups
quest/m1/ts-atsc-ac3, added here: 48 kHz ATSC AC-3 (ffmpeg's carriage, stream type 0x81, a 2,592-byte main buffer) abortsexport tswith a missed decode deadline at every rate from 384 kb/s up, onmainas with this PR, so the--headroomarm runs its AC-3 at 192 kb/s. The schedule frees a unit's decoder-buffer bytes a slot after its due slot rather than when it decodes, and 32 ms AC-3 frames on a 25 ms grid then never fit two to the buffer. A 44.1 or 32 kHz frame that fits goes out like any other, and one that outgrows the buffer fails the export naming both sizes. Ranked in m1 just after Multi-packet PMT; @kixelated, move it if it belongs elsewhere.main. Carrying each table once per slot breaks the AAC program config's per-unit tune-in points, so it wants each later group tied to its own unit instead. A narrower fix, dropping a copy only where it would be laid right after an identical run, is proposed in review and not pushed.Planning decisions for
quest/m1/ts-atsc-ac3Goal.
moq export tscarries ATSC AC-3 at every rate A/52 allows, without aborting on a missed deadline, and passes the strict T-STD check. Which scope?Placement. Where should the quest sit?
Approach. How should the fix work?
Verification. How should the fix be verified?
Other sample rates (after CodeRabbit's review). A/53 caps ATSC main audio at 48 kHz and 448 kb/s, and at 44.1 kHz above about 595 kb/s, or 32 kHz from 448 kb/s, one frame is bigger than the 2,592 B buffer. How should the scope read?
Reconciling with the 48 kHz scope (after @kixelated scoped the quest to 48 kHz and left 44.1 and 32 kHz open). How should the quest read?
Review decisions: repeated tables in a slot
Codex found that keyframes aligned across video PIDs can put several PAT/PMT copies back to back. What should this PR do?
After @kixelated reverted a once-per-slot drop for breaking the AAC program config's tune-in points, and the fix was narrowed to a copy laid right after an identical run (which keeps them), what now?
Closes #5142
(Written by Claude Opus 5.5)