T2: realtime capture tail trimming

Auto/Manual/Off tail handling for realtime track-tap capture. Auto scans
recorded PCM backward for last frame above -72 dB and truncates the wav
header-aware (8 s cap); Manual pads a fixed tail; Off is byte-identical.
wav_trim rejects WAVE_FORMAT_EXTENSIBLE with non-float SubFormat GUID.
This commit is contained in:
2026-07-23 18:25:45 -04:00
parent 81fa37fe94
commit f2bfe466ec
12 changed files with 1053 additions and 10 deletions
+182 -5
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@@ -71,13 +71,18 @@
#include <chrono>
#include <cstdint>
#include <cstring>
#include <ctime>
#include <filesystem>
#include <fstream>
#include <string>
#include <vector>
#include "capture_paths.h"
#include "peaks.h" // lastFrameAboveThreshold, AudioSample
#include "realtime_record.h"
#include "render_settings.h" // autoTrimEndRatio, realtimeRecordWindowEnd
#include "wav_trim.h" // parseWavLayout, extractFloatFrames, planWavTruncate
#define REAPERAPI_MINIMAL
#define REAPERAPI_WANT_EnumProjects
@@ -178,6 +183,12 @@ public:
BankPaths paths_;
std::string uniqueTag_;
// The RECORDED window end in project seconds (>= request_.endSeconds). For a tail
// mode the transport runs PAST the range end (Auto: +8 s cap; Manual: +the set
// length), so this — not request_.endSeconds — is the end the completion state
// machine waits for. Equals request_.endSeconds for TailMode::None (exact bounds).
double recordWindowEnd_ = 0.0;
// The transient sink. The sends we create (from each selected source track INTO
// temp_) live on those source tracks pointing AT temp_, and are removed automatically
// when temp_ is deleted — REAPER cannot leave a send dangling to a deleted
@@ -311,6 +322,128 @@ private:
namespace {
// Reads the whole file into a byte buffer. Empty vector on any I/O failure — the
// caller treats an unreadable file as "skip the trim" (keep the untrimmed window),
// never as a corruption of the recorded audio.
std::vector<std::uint8_t> readAllBytes(const std::string& path) {
std::ifstream f(path, std::ios::binary | std::ios::ate);
if (!f) return {};
const std::streamoff size = f.tellg();
if (size <= 0) return {};
std::vector<std::uint8_t> bytes(static_cast<std::size_t>(size));
f.seekg(0);
f.read(reinterpret_cast<char*>(bytes.data()), size);
if (!f) return {};
return bytes;
}
// Patches a little-endian uint32 into a byte buffer at `off` (the header size fields).
void writeU32LE(std::vector<std::uint8_t>& bytes, std::size_t off, std::uint32_t v) {
bytes[off + 0] = static_cast<std::uint8_t>(v & 0xFF);
bytes[off + 1] = static_cast<std::uint8_t>((v >> 8) & 0xFF);
bytes[off + 2] = static_cast<std::uint8_t>((v >> 16) & 0xFF);
bytes[off + 3] = static_cast<std::uint8_t>((v >> 24) & 0xFF);
}
// ============================================================================
// §TAIL — Auto-mode PCM decay-scan trim (docs/product/capture-tail.md §realtime)
// ============================================================================
// After the recorded file is stable and moved into the bank (the file we OWN — never
// the project), Auto mode trims the trailing decay: read the WAV, scan the tail
// region (frames AFTER the original range end) backward for the last frame above
// -72 dB, and truncate the file there. Rules (spec):
// * no frame in the tail window above -72 dB -> trim back to the original range end
// * signal never falls below -72 dB in window -> keep the full window (cap did its job)
// * otherwise -> trim one frame past the last audible
//
// Returns the trimmed length in SECONDS (for the Sample), or a negative value to
// signal "no trim applied" (caller keeps the pre-trim length). Best-effort and
// non-fatal: any unreadable/unknown/short file skips the trim (keeps the full window)
// rather than risk corrupting the capture — realtime tail is a convenience path.
//
// FORMAT / FLUSH ASSUMPTIONS (DAW-verify): the recorded file is a canonical 32-bit
// float WAV (REAPER project record format — the manual procedure sets it) and is fully
// flushed/closed before this runs (the tick() Finalizing size-stable wait guarantees
// that for the normal path; abort()'s best-effort finalize races it, documented).
double trimAutoTailInPlace(const std::string& path,
double rangeStartSeconds,
double rangeEndSeconds) {
constexpr double kNoTrim = -1.0;
std::vector<std::uint8_t> bytes = readAllBytes(path);
if (bytes.empty()) return kNoTrim;
const reasampler::WavLayout layout = parseWavLayout(bytes);
if (!layout.valid || layout.sampleRate == 0) return kNoTrim; // not a WAV we trim
const std::size_t totalFrames = layout.frameCount();
if (totalFrames == 0) return kNoTrim;
// The original range end as a frame index within the file (frame 0 == start). Use
// the FILE's own sample rate (authoritative) — the request rate may be 0 (=follow
// project). Clamp to the file so a rounding overshoot cannot exceed it.
const double rangeSeconds = rangeEndSeconds - rangeStartSeconds;
if (rangeSeconds <= 0.0) return kNoTrim;
std::size_t rangeEndFrame = static_cast<std::size_t>(
rangeSeconds * static_cast<double>(layout.sampleRate) + 0.5);
if (rangeEndFrame > totalFrames) rangeEndFrame = totalFrames;
// Nothing recorded past the range end (the tail window was empty) -> nothing to
// trim; keep as-is. (Shouldn't happen for Auto, but total by construction.)
if (rangeEndFrame >= totalFrames) return kNoTrim;
// Scan ONLY the tail region (frames after the original range end). The trim never
// eats into the range body — the scan starts at rangeEndFrame.
const std::size_t tailFrames = totalFrames - rangeEndFrame;
const std::vector<reasampler::AudioSample> tailPcm =
extractFloatFrames(bytes, layout, rangeEndFrame, tailFrames);
if (tailPcm.empty()) return kNoTrim;
const float threshold = static_cast<float>(reasampler::autoTrimEndRatio());
const std::size_t lastAbove = reasampler::lastFrameAboveThreshold(
tailPcm, layout.channelCount, tailFrames, threshold);
// keptFrames: the total frame count the trimmed file retains.
// no audible tail frame -> trim back to the range end (rangeEndFrame frames)
// an audible frame at idx -> keep range body + up to and including that frame
// The "signal never falls below threshold" case falls out naturally: lastAbove is
// the final tail frame, so keptFrames == totalFrames (the full window is kept).
std::size_t keptFrames;
if (lastAbove == reasampler::kNoFrameAboveThreshold) {
keptFrames = rangeEndFrame;
} else {
keptFrames = rangeEndFrame + (lastAbove + 1);
}
if (keptFrames >= totalFrames) return kNoTrim; // full window kept -> no truncate
const reasampler::WavTruncatePlan plan = planWavTruncate(layout, keptFrames);
if (!plan.valid) return kNoTrim;
// Patch the RIFF + data size fields in the in-memory buffer so they describe the
// kept frame count, then rewrite the file as exactly the first newFileByteLength
// bytes (header + patched sizes + retained PCM). A single truncating write is the
// simplest correct truncate — no separate resize step, no partial-write window
// where the on-disk sizes and length disagree. The result is a valid, playable WAV
// of the kept frames (verified by the wav_trim re-parse test).
writeU32LE(bytes, plan.dataSizeFieldOffset, plan.newDataSize);
writeU32LE(bytes, plan.riffSizeFieldOffset, plan.newRiffSize);
// NOTE (DAW-verify, best-effort): a truncating write that fails MID-write (a full
// disk, a yanked drive) would leave a short file while we return kNoTrim, so the
// Sample length would overstate the file. Vanishingly unlikely for a just-recorded
// local bank file, and realtime tail is a convenience path, so a temp-file+atomic-
// rename is not warranted here; flagged rather than built.
std::ofstream out(path, std::ios::binary | std::ios::trunc);
if (!out) return kNoTrim; // could not reopen to rewrite — leave the full file
out.write(reinterpret_cast<const char*>(bytes.data()),
static_cast<std::streamsize>(plan.newFileByteLength));
if (!out) return kNoTrim;
out.close();
// The trimmed length in seconds for the Sample metadata.
return static_cast<double>(keptFrames) / static_cast<double>(layout.sampleRate);
}
// Builds a CaptureResult for a finalized recording: discover the recorded file,
// move it into the bank, populate the Sample via the pure mapping. Returns Ok +
// Sample on success, or a RenderFailed result. Does NOT restore — the caller
@@ -347,6 +480,19 @@ CaptureResult finalizeRecording(RealtimeCaptureState& st) {
std::filesystem::remove(recorded, rmEc); // best-effort
}
// TAIL (Auto): trim the trailing decay of the recorded window in place — on the
// BANK file we now own (destPath), never the project. Best-effort: an unreadable /
// unknown-format / short file skips the trim (keeps the full window) rather than
// corrupt the capture. Only Auto trims; None recorded exact bounds and Manual is a
// fixed window (spec §The realtime path). Returns the trimmed length in seconds,
// or < 0 for "no trim applied".
double trimmedLenSeconds = -1.0;
if (st.request_.tailMode == TailMode::Auto) {
trimmedLenSeconds = trimAutoTailInPlace(destPath,
st.request_.startSeconds,
st.request_.endSeconds);
}
RecordedCapture cap;
cap.relativePath = st.paths_.relativePath;
cap.uniqueTag = st.uniqueTag_;
@@ -365,9 +511,25 @@ CaptureResult finalizeRecording(RealtimeCaptureState& st) {
result.status = CaptureStatus::Ok;
result.sample = sampleFromRecordedCapture(cap);
// The recorded file's true length differs from the request range when a tail was
// recorded, so the Sample length must reflect the FILE, not the range:
// Auto with a trim applied -> the trimmed length trimAutoTailInPlace returned.
// Auto with no trim, or Manual -> the full recorded window (end - start).
// None -> the exact range (unchanged; recordWindowEnd_ == endSeconds).
// sampleFromRecordedCapture already set lengthSeconds = end - start; override it
// to the recorded/trimmed length so downstream (thumbnail, placement) matches disk.
if (trimmedLenSeconds >= 0.0) {
result.sample.lengthSeconds = trimmedLenSeconds;
} else {
result.sample.lengthSeconds =
st.recordWindowEnd_ - st.request_.startSeconds;
}
result.message = "Realtime-captured [" +
std::to_string(st.request_.startSeconds) + "s, " +
std::to_string(st.request_.endSeconds) + "s] -> " +
std::to_string(st.request_.endSeconds) + "s] (recorded " +
std::to_string(result.sample.lengthSeconds) + "s) -> " +
st.paths_.relativePath;
return result;
}
@@ -448,6 +610,14 @@ RealtimeRecordBackend::begin(const CaptureRequest& request,
st->uniqueTag_ = makeUniqueTag();
st->paths_ = deriveBankPaths(projectDir, request.baseName, st->uniqueTag_);
// The recorded window end: extended past the range end for a tail mode (Auto/Manual),
// exact for None. This — not request.endSeconds — is what the completion machine
// waits for; the extra window past the range end is trimmed later (Auto) or kept
// (Manual). Pure mapping (render_settings), shared caps with the offline tail.
st->recordWindowEnd_ = realtimeRecordWindowEnd(request.tailMode,
request.endSeconds,
request.tailMs);
// DELIBERATE: the transient temp-track / arm / send / transport mutations are NOT
// wrapped in an Undo_BeginBlock/Undo_EndBlock — divergence from the insert/view
// shells is intentional. This backend fully restores its own state across every
@@ -514,9 +684,12 @@ RealtimeRecordBackend::begin(const CaptureRequest& request,
SetMediaTrackInfo_Value(st->temp_, "I_RECARM", 1.0); // arm ONLY the sink
SetMediaTrackInfo_Value(st->temp_, "I_RECMON", 0.0); // no input monitoring
// Record range: time selection over [start,end], play cursor at start. Both were
// snapshotted and will be restored by restore().
double rs = request.startSeconds, re = request.endSeconds;
// Record range: time selection over [start, recordWindowEnd], play cursor at start.
// recordWindowEnd extends past the request's range end for a tail mode so the
// transport captures the decaying tail; it equals the range end for None (exact
// bounds). Both cursor + time selection were snapshotted and are restored by
// restore().
double rs = request.startSeconds, re = st->recordWindowEnd_;
GetSet_LoopTimeRange(true, false, &rs, &re, false);
SetEditCurPos(request.startSeconds, false, false);
@@ -567,9 +740,13 @@ RealtimeTickResult RealtimeRecordBackend::tick(RealtimeCaptureState& state) {
state.lastFileSize_ = sz;
}
// Wait for the transport to reach the RECORDED window end (extended past the
// range end for a tail mode), not the request's range end — the extra tail window
// is part of the record. The record safety ceiling scales with it (window - start
// + margin) inside the pure machine.
state.phase_ = advanceRecordPhase(state.phase_, inputs,
state.request_.startSeconds,
state.request_.endSeconds);
state.recordWindowEnd_);
// On the Recording -> Finalizing edge, stop OUR project's transport ONCE so REAPER
// begins closing/flushing the recorded take. Project-scoped (OnStopButtonEx(proj_))
+18 -4
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@@ -596,13 +596,20 @@ static void RunCaptureRealtimeTrack()
return;
}
// The tail mode is the SAME panel setting the offline capture actions read (the
// docked bank panel's toggle). Realtime honors it via a parallel path: the backend
// records a generous window past the range end, then trims by PCM decay-scan (T2 /
// capture-tail.md §The realtime path) — it does NOT drive RENDER_*. Default None
// keeps realtime exact-bounds / byte-identical to today.
const reasampler::TailSetting tail = reasampler::bankPanelTailSetting();
reasampler::CaptureRequest req;
req.sourceMode = reasampler::SourceMode::SelectedTracks; // realtime track scope
req.startSeconds = src.startSeconds; // exact bounds — no rounding
req.endSeconds = src.endSeconds;
req.wetDry = 1.0; // fully wet (post-fader tap)
req.tailMode = reasampler::TailMode::None; // realtime tail is T2; exact bounds here
req.tailMs = 0.0;
req.tailMode = tail.mode; // None / Auto / Manual, from the panel toggle
req.tailMs = tail.manualMs; // Manual-only (pre-clamped); ignored for None/Auto
req.sampleRate = 0; // follow project rate
req.channelCount = 2;
req.bitDepth = reasampler::WavBitDepth::Float32;
@@ -623,8 +630,15 @@ static void RunCaptureRealtimeTrack()
// completion across ticks (UI stays responsive).
g_rtCaptureProject = EnumProjects(-1, nullptr, 0);
g_rtCapture = std::move(st);
ShowConsoleMsg("ReaSampler: realtime capture started — recording in the "
"background; the bank updates when it reaches the range end.\n");
// With a tail mode the recorded window runs PAST the range end (Auto: +8 s then
// decay-trim; Manual: +the set length), so the completion note names the window,
// not just the range end.
const char* doneWhen =
(tail.mode == reasampler::TailMode::None)
? "the bank updates when it reaches the range end."
: "the bank updates after the extra tail window (past the range end).";
ShowConsoleMsg((std::string("ReaSampler: realtime capture started — recording in "
"the background; ") + doneWhen + "\n").c_str());
}
// Cancels the in-flight realtime capture on demand (bindable action). Force-terminates
+28
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@@ -2,6 +2,7 @@
#include <algorithm>
#include <climits>
#include <cmath>
// peaks implementation.
//
@@ -63,4 +64,31 @@ Envelope computeEnvelope(const std::vector<AudioSample>& interleaved,
return envelope;
}
std::size_t lastFrameAboveThreshold(const std::vector<AudioSample>& interleaved,
std::size_t channelCount,
std::size_t frameCount,
AudioSample linearThreshold) {
if (channelCount == 0) return kNoFrameAboveThreshold;
// Clamp to what the buffer actually holds — a caller frameCount that overstates
// the buffer must never read past the end (mirror of computeEnvelope's guard).
const std::size_t availableFrames = interleaved.size() / channelCount;
const std::size_t frames = std::min(frameCount, availableFrames);
if (frames == 0) return kNoFrameAboveThreshold;
// Scan backward: the first frame (from the end) whose loudest channel exceeds the
// threshold is the last audible frame. `f` runs frames..1 so `f-1` never wraps.
for (std::size_t f = frames; f > 0; --f) {
const std::size_t frame = f - 1;
const std::size_t base = frame * channelCount;
AudioSample peak = 0.0f;
for (std::size_t c = 0; c < channelCount; ++c) {
const AudioSample a = std::fabs(interleaved[base + c]);
peak = std::max(peak, a);
}
if (peak > linearThreshold) return frame;
}
return kNoFrameAboveThreshold;
}
} // namespace reasampler
+38
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@@ -66,4 +66,42 @@ Envelope computeEnvelope(const std::vector<AudioSample>& interleaved,
std::size_t frameCount,
std::size_t binCount);
// Sentinel returned by lastFrameAboveThreshold when NO frame in the scanned range
// peaks above the threshold (pure silence at that level). SIZE_MAX is unambiguous:
// no valid frame index can equal it (a real index is < frameCount <= SIZE_MAX for
// any allocatable buffer), so the caller tests `== kNoFrameAboveThreshold` cleanly.
inline constexpr std::size_t kNoFrameAboveThreshold =
static_cast<std::size_t>(-1);
// Scans interleaved PCM BACKWARD for the last frame whose per-frame peak (the max
// absolute value across all channels of that frame — NO stereo fold, just the
// loudest channel that frame) exceeds `linearThreshold`, returning that frame index.
// Returns kNoFrameAboveThreshold if no frame exceeds it (or on degenerate input).
//
// This is the boundary primitive behind the realtime tail's decay-scan trim
// (docs/product/capture-tail.md §The realtime path): the recorded tail window is
// scanned back from the end for the last frame still above -72 dB, and the file is
// truncated one frame past it. Deliberately a separate primitive from
// computeEnvelope — that answers "the min/max envelope over bins" (a thumbnail),
// this answers "the last frame above a level" (a boundary). Bending the bin-oriented
// envelope to a frame-exact boundary question is a worse fit (spec §option a).
//
// interleaved frame-interleaved samples: [f0c0, f0c1, ..., f1c0, f1c1, ...].
// Must hold >= frameCount * channelCount; extra is ignored, and a
// short buffer is clamped to what it actually holds (no OOB read).
// channelCount channels per frame (the stride). The per-frame test is the max
// |sample| over these channels — the frame is "above" if its
// loudest channel is above the threshold.
// frameCount frames to consider (the scan starts at the last of these).
// linearThreshold the comparison level as a LINEAR amplitude ratio (e.g. the
// -72 dB ratio from render_settings::autoTrimEndRatio), NOT dB.
// A frame counts as above when its peak is STRICTLY > this.
//
// Pure, stdlib-only, unit-tested (a synthetic decaying ramp, silence, all-above,
// and degenerate inputs) so the trim boundary math is locked outside the DAW.
std::size_t lastFrameAboveThreshold(const std::vector<AudioSample>& interleaved,
std::size_t channelCount,
std::size_t frameCount,
AudioSample linearThreshold);
} // namespace reasampler
+18
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@@ -56,6 +56,24 @@ TailRenderSettings tailRenderSettingsFor(TailMode mode, double manualTailMs) {
return t;
}
double realtimeRecordWindowEnd(TailMode mode, double rangeEndSeconds,
double manualTailMs) {
switch (mode) {
case TailMode::None:
// Exact — no extra recording (byte-identical to today's realtime capture).
return rangeEndSeconds;
case TailMode::Auto:
// The 8 s runaway cap past the range end; the decay-trim shortens it later.
return rangeEndSeconds + kMaxTailSeconds;
case TailMode::Manual:
// Fixed window: range + the set length, clamped to the 8 s cap (the same
// runaway guard the offline Manual path applies). Negative floors to 0.
return rangeEndSeconds + std::clamp(manualTailMs, 0.0, kMaxTailMs) / 1000.0;
}
// Unreachable for a valid enum; fail closed to exact bounds (never a stray tail).
return rangeEndSeconds;
}
RenderSettingsChoice renderSettingsFor(SourceMode mode, double /*wetDry*/) {
// `wetDry` is accepted so CaptureRequest.wetDry remains the seam for future
// dry work (M10 null test), but it does not affect this mapping. FX scoping is
+14
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@@ -114,6 +114,20 @@ struct TailRenderSettings {
// the Auto default or an explicit request (spec §Manual override). Pure + tested.
TailRenderSettings tailRenderSettingsFor(TailMode mode, double manualTailMs);
// The REALTIME record-window end (in project seconds) a tail mode records to, given
// the request's exact range end (docs/product/capture-tail.md §The realtime path).
// Realtime does NOT drive RENDER_*; it records a generous window and trims later, so
// the window end is where the transport actually stops:
// None -> rangeEndSeconds (exact — no extra recording).
// Auto -> rangeEndSeconds + kMaxTailSeconds (the 8 s runaway cap; trimmed later).
// Manual -> rangeEndSeconds + clamp(manualTailMs, kMaxTailMs)/1000 (fixed, no trim).
// `manualTailMs` is used ONLY for Manual. Pure so the mode->window arithmetic (and
// the Manual clamp) is unit-tested outside the DAW; the backend applies the returned
// end to the record time selection. Shared -72 dB / 8 s constants are the same ones
// the offline tail uses (single source of truth).
double realtimeRecordWindowEnd(TailMode mode, double rangeEndSeconds,
double manualTailMs);
// The RENDER_SETTINGS value for a given source mode. `supported` is false only
// for SourceMode::Realtime (that is the M8 backend, not offline render).
struct RenderSettingsChoice {
+160
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@@ -0,0 +1,160 @@
// wav_trim — pure implementation. See wav_trim.h. NO REAPER / SWELL / vendor.
#include "wav_trim.h"
#include <cstring> // std::memcpy, std::memcmp
namespace reasampler {
namespace {
// Little-endian readers. Bounds are checked by the caller before each read; these
// assume `off + N <= bytes.size()`. memcpy avoids alignment/aliasing UB.
std::uint16_t readU16LE(const std::vector<std::uint8_t>& b, std::size_t off) {
return static_cast<std::uint16_t>(b[off] | (b[off + 1] << 8));
}
std::uint32_t readU32LE(const std::vector<std::uint8_t>& b, std::size_t off) {
return static_cast<std::uint32_t>(b[off]) |
(static_cast<std::uint32_t>(b[off + 1]) << 8) |
(static_cast<std::uint32_t>(b[off + 2]) << 16) |
(static_cast<std::uint32_t>(b[off + 3]) << 24);
}
bool tagEquals(const std::vector<std::uint8_t>& b, std::size_t off, const char* tag) {
return off + 4 <= b.size() && std::memcmp(b.data() + off, tag, 4) == 0;
}
// WAVE format tags we accept as 32-bit float (see wav_trim.h FORMAT ASSUMPTION).
constexpr std::uint16_t kWaveFormatIeeeFloat = 0x0003;
constexpr std::uint16_t kWaveFormatExtensible = 0xFFFE;
} // namespace
WavLayout parseWavLayout(const std::vector<std::uint8_t>& bytes) {
WavLayout out;
// Minimum viable RIFF/WAVE: "RIFF"(4) size(4) "WAVE"(4) = 12 bytes.
if (bytes.size() < 12) return out;
if (!tagEquals(bytes, 0, "RIFF")) return out;
if (!tagEquals(bytes, 8, "WAVE")) return out;
bool haveFmt = false;
std::uint16_t fmtTag = 0, channels = 0, bitsPerSample = 0;
std::uint32_t sampleRate = 0;
std::uint16_t extensibleSubFormatTag = 0; // set only when fmtTag == kWaveFormatExtensible
// Walk the sub-chunks after "WAVE" (offset 12). Each is: id(4) size(4) body(size),
// body padded to an even byte count (RIFF word alignment). Stop cleanly if a
// header would run past the buffer — a malformed/truncated file is "invalid",
// never an OOB read.
std::size_t pos = 12;
while (pos + 8 <= bytes.size()) {
const std::size_t bodyOffset = pos + 8;
const std::uint32_t bodySize = readU32LE(bytes, pos + 4);
if (tagEquals(bytes, pos, "fmt ")) {
// fmt body: at least 16 bytes (PCM/float common fields).
if (bodyOffset + 16 > bytes.size() || bodySize < 16) return out;
fmtTag = readU16LE(bytes, bodyOffset + 0);
channels = readU16LE(bytes, bodyOffset + 2);
sampleRate = readU32LE(bytes, bodyOffset + 4);
bitsPerSample = readU16LE(bytes, bodyOffset + 14);
// For WAVE_FORMAT_EXTENSIBLE (0xFFFE), read the SubFormat GUID's leading
// 2-byte tag at body offset 24 to distinguish float (0x0003) from PCM
// integer (0x0001) and all other sub-formats. Body must be >= 40 bytes to
// reach GUID offset 24 + 16 bytes of GUID, and the full GUID must fit in
// the buffer; otherwise we leave extensibleSubFormatTag at 0 (rejected).
if (fmtTag == kWaveFormatExtensible) {
if (bodySize >= 40 && bodyOffset + 40 <= bytes.size()) {
extensibleSubFormatTag = readU16LE(bytes, bodyOffset + 24);
}
}
haveFmt = true;
} else if (tagEquals(bytes, pos, "data")) {
// The data chunk: PCM starts at bodyOffset, declared length bodySize.
// Reject if it runs past the buffer (truncated / lying header).
if (bodyOffset + bodySize > bytes.size()) return out;
if (!haveFmt) return out; // data before fmt — not a WAV we parse
// Plain IEEE-float tag (0x0003): accept as-is.
// Extensible tag (0xFFFE): accept only when the SubFormat tag read from
// the GUID at body offset 24 is also 0x0003 (IEEE float). SubFormat tag
// 0x0001 (PCM integer) or anything else with bitsPerSample==32 is NOT
// float and must be rejected to prevent mis-decoding as float.
const bool floatTag = (fmtTag == kWaveFormatIeeeFloat) ||
(fmtTag == kWaveFormatExtensible &&
extensibleSubFormatTag == kWaveFormatIeeeFloat);
if (!floatTag || bitsPerSample != 32 || channels == 0) return out;
out.valid = true;
out.channelCount = channels;
out.sampleRate = sampleRate;
out.dataByteOffset = bodyOffset;
out.dataByteLength = bodySize;
out.riffSizeFieldOffset = 4;
out.dataSizeFieldOffset = pos + 4; // the `data` size field (LE uint32)
return out;
}
// Advance past this chunk's body, honoring RIFF even-byte padding. Guard the
// additions against size_t overflow (a hostile bodySize near SIZE_MAX).
std::size_t advance = bodySize;
if (advance & 1u) ++advance; // pad byte
if (advance > bytes.size() - bodyOffset) break; // would overrun -> stop
pos = bodyOffset + advance;
}
return out; // no data chunk found -> invalid
}
std::vector<AudioSample> extractFloatFrames(const std::vector<std::uint8_t>& bytes,
const WavLayout& layout,
std::size_t startFrame,
std::size_t frameCount) {
std::vector<AudioSample> out;
if (!layout.valid) return out;
const std::size_t bytesPerFrame =
static_cast<std::size_t>(layout.channelCount) * 4u;
const std::size_t totalFrames = layout.frameCount();
if (startFrame >= totalFrames) return out;
// Clamp the requested span to the frames that actually exist.
const std::size_t avail = totalFrames - startFrame;
const std::size_t frames = (frameCount < avail) ? frameCount : avail;
if (frames == 0) return out;
const std::size_t firstByte =
layout.dataByteOffset + startFrame * bytesPerFrame;
out.resize(frames * layout.channelCount);
// memcpy each float (LE on target hosts — see header's byte-order note).
for (std::size_t i = 0; i < out.size(); ++i) {
float f = 0.0f;
std::memcpy(&f, bytes.data() + firstByte + i * 4u, 4u);
out[i] = f;
}
return out;
}
WavTruncatePlan planWavTruncate(const WavLayout& layout, std::size_t keptFrames) {
WavTruncatePlan plan;
if (!layout.valid) return plan;
const std::size_t totalFrames = layout.frameCount();
if (keptFrames > totalFrames) return plan; // never grow
const std::size_t bytesPerFrame =
static_cast<std::size_t>(layout.channelCount) * 4u;
const std::size_t keptDataBytes = keptFrames * bytesPerFrame;
plan.valid = true;
plan.newFileByteLength = layout.dataByteOffset + keptDataBytes;
plan.dataSizeFieldOffset = layout.dataSizeFieldOffset;
plan.newDataSize = static_cast<std::uint32_t>(keptDataBytes);
plan.riffSizeFieldOffset = layout.riffSizeFieldOffset;
// RIFF size counts everything after the 8-byte "RIFF"+size prefix.
plan.newRiffSize = static_cast<std::uint32_t>(plan.newFileByteLength - 8);
return plan;
}
} // namespace reasampler
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#pragma once
// wav_trim — pure parse + truncate-plan for the realtime tail's PCM decay-scan trim.
//
// PURE MODULE (CLAUDE.md §load-bearing split): NO REAPER types, NO SWELL, NO
// vendor/ includes. Standard library only. Builds and unit-tests without REAPER.
//
// WHY THIS EXISTS (docs/product/capture-tail.md §The realtime path). The realtime
// backend records a generous tail window, then trims the trailing decay by
// truncating the recorded WAV at a frame boundary. Truncating a WAV correctly is
// not "chop the bytes": the RIFF container's size fields (the top-level RIFF chunk
// size and the `data` sub-chunk size) must be patched to the kept byte count, or
// the file is a corrupt / mis-lengthed WAV. That header arithmetic — chunk walking,
// format verification, and the size-field patch offsets — is exactly the fiddly,
// easy-to-get-wrong logic the discipline unit-tests OUTSIDE the DAW. The REAPER
// shell (capture_realtime.cpp) does only the file I/O: read the bytes, call the
// pure parse, run the decay scan, call the pure plan, write the truncated bytes.
//
// FORMAT ASSUMPTION (flagged for DAW-verify). We record 32-bit float WAV
// (capture.cpp kRenderFormatWavFloat32; realtime records via REAPER's project
// record format, which the manual procedure sets to WAV/32-bit-float). This parser
// therefore verifies canonical PCM/IEEE-float WAV: a RIFF/WAVE container, a `fmt `
// chunk declaring 32-bit float (format tag 3, or tag 0xFFFE WAVE_FORMAT_EXTENSIBLE
// with 32 bits), and a `data` chunk of interleaved little-endian float32. Anything
// else (a different depth, a non-WAV, a compressed source) is reported invalid and
// the shell SKIPS the trim (keeps the untrimmed window) rather than corrupting a
// file it does not understand. This is deliberately conservative.
#include <cstddef>
#include <cstdint>
#include <vector>
#include "peaks.h" // AudioSample (float)
namespace reasampler {
// The parsed geometry of a canonical 32-bit-float WAV. `valid` is false when the
// bytes are not a WAV we can safely trim (see FORMAT ASSUMPTION); every other field
// is meaningful only when valid.
struct WavLayout {
bool valid = false;
std::uint16_t channelCount = 0; // from `fmt ` (the interleave stride)
std::uint32_t sampleRate = 0; // from `fmt ` (for frame<->seconds, if needed)
// The `data` chunk: byte offset of its first PCM byte within the file, and its
// declared PCM byte length. frameCount = dataByteLength / (channelCount * 4).
std::size_t dataByteOffset = 0;
std::size_t dataByteLength = 0;
// Byte offset of the two little-endian uint32 size fields the truncate patch
// rewrites: the top-level RIFF chunk size (bytes 4..7) and the `data` sub-chunk
// size (the 4 bytes immediately before dataByteOffset).
std::size_t riffSizeFieldOffset = 4; // always 4 for a RIFF file
std::size_t dataSizeFieldOffset = 0;
std::size_t frameCount() const {
const std::size_t bytesPerFrame = static_cast<std::size_t>(channelCount) * 4u;
return bytesPerFrame ? dataByteLength / bytesPerFrame : 0;
}
};
// Parses a WAV byte buffer's header geometry. Returns {valid=false} for anything
// that is not a canonical 32-bit-float RIFF/WAVE with a `fmt ` and a `data` chunk,
// or whose declared `data` length runs past the buffer. Does NOT copy PCM — it only
// locates it (extractFloatFrames does the copy). Pure + total (no throw, no UB).
WavLayout parseWavLayout(const std::vector<std::uint8_t>& bytes);
// Copies `frameCount` interleaved float frames starting at `startFrame` out of the
// WAV's `data` region into a flat [f0c0,f0c1,...] buffer (the shape peaks consumes).
// Clamps to the frames the buffer actually holds — never reads past `data`. Returns
// empty for an invalid layout or an out-of-range start. The floats are read
// little-endian via std::memcpy (no aliasing UB); on a big-endian host they would
// need a byte-swap — flagged, not handled, because the target (Windows/macOS/Linux
// on x86/ARM-LE) is little-endian and REAPER writes LE WAV.
std::vector<AudioSample> extractFloatFrames(const std::vector<std::uint8_t>& bytes,
const WavLayout& layout,
std::size_t startFrame,
std::size_t frameCount);
// The plan to truncate a parsed WAV to `keptFrames` frames: the new total file byte
// length and the two size-field values to patch. `valid` is false if the layout is
// invalid or keptFrames exceeds the file's frames (never GROW a file — the caller
// clamps beforehand; this guards it too).
struct WavTruncatePlan {
bool valid = false;
std::size_t newFileByteLength = 0; // truncate the file to exactly this length
std::size_t dataSizeFieldOffset = 0; // where to write newDataSize (LE uint32)
std::uint32_t newDataSize = 0; // kept PCM byte length
std::size_t riffSizeFieldOffset = 4; // where to write newRiffSize (LE uint32)
std::uint32_t newRiffSize = 0; // newFileByteLength - 8 (RIFF size excludes
// the 8-byte "RIFF"+size prefix)
};
// Computes the truncate plan to keep exactly `keptFrames` frames of a parsed WAV.
// keptFrames == layout.frameCount() is a valid no-op plan (file unchanged). Pure +
// total. The shell applies it: patch the two size fields in the byte buffer, then
// truncate the file to newFileByteLength.
WavTruncatePlan planWavTruncate(const WavLayout& layout, std::size_t keptFrames);
} // namespace reasampler