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MP4: merge the QT chapter reference into an existing tref (#1408)
A trak may hold at most one tref. setQtChapters() appended a second one for the chap reference instead of joining the atom already present, which happens whenever the audio track references another track -- a timecode track, as in camera recordings. Parsers differ on the result: the lenient keep reading the track, the strict discard it entirely. A file written this way therefore still reads correctly in TagLib while presenting as having no audio elsewhere, and anything that remuxes it from a stricter parser's track list writes an audioless copy back to disk. Removal follows the same rule inverted: only the chap box is taken out when the tref is shared, and the tref itself goes only when chap was its sole child. It also now looks for the tref that actually contains chap rather than the first one on the track, so a file already carrying two is repaired rather than stripped of the wrong reference.
This commit is contained in:
Ryan Francesconi
+142
-41
@@ -690,13 +690,68 @@ namespace
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// -- tref / chap builder --------------------------------------------------
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//! Builds a tref atom containing a chap reference to the given track ID.
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ByteVector buildTref(unsigned int chapterTrackId)
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//! Builds a chap reference box pointing at the given track ID.
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ByteVector buildChap(unsigned int chapterTrackId)
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{
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ByteVector chapData;
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chapData.append(ByteVector::fromUInt(chapterTrackId));
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const ByteVector chap = renderAtom("chap", chapData);
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return renderAtom("tref", chap);
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return renderAtom("chap", chapData);
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}
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//! Builds a tref atom containing a chap reference to the given track ID.
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ByteVector buildTref(unsigned int chapterTrackId)
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{
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return renderAtom("tref", buildChap(chapterTrackId));
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}
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//! The track's tref atom, or null when it has none.
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//!
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//! A trak carries at most one tref; a second one makes AVFoundation discard the
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//! whole track, so a chapter reference has to join the existing atom rather than
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//! bring its own.
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MP4::Atom *findTrefAtom(const MP4::Atom *trak)
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{
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if(!trak)
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return nullptr;
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for(const auto &child : trak->children()) {
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if(child->name() == "tref")
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return child;
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}
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return nullptr;
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}
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//! Locates a reference box of the given type inside a tref.
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//!
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//! \return true when found, setting \a boxOffset and \a boxLength.
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bool findTrefEntry(TagLib::File *file, const MP4::Atom *tref,
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const ByteVector &type, offset_t &boxOffset,
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offset_t &boxLength)
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{
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if(!tref)
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return false;
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const offset_t trefEnd = tref->offset() + tref->length();
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file->seek(tref->offset() + 8);
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while(file->tell() + 8 <= trefEnd) {
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const offset_t boxStart = file->tell();
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const ByteVector header = file->readBlock(8);
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if(header.size() < 8)
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break;
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const unsigned int boxSize = header.toUInt();
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if(boxSize < 8)
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break;
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if(header.mid(4, 4) == type) {
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boxOffset = boxStart;
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boxLength = static_cast<offset_t>(boxSize);
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return true;
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}
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file->seek(boxStart + boxSize);
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}
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return false;
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}
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// -- Reading helpers ------------------------------------------------------
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@@ -923,27 +978,63 @@ namespace
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//! Removes the tref atom from the audio track.
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//! Updates trak size, parent sizes, and chunk offsets.
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//! audioTrak's in-memory children list is NOT modified (caller re-parses if needed).
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void removeAudioTref(TagLib::File *file, const MP4::Atoms *atoms, const MP4::Atom *audioTrak)
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//! Removes the chapter reference from the audio track.
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//!
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//! The chap box can share the track's single tref with references to other tracks
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//! -- a timecode track, for instance -- so only chap is removed in that case.
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//! The tref itself goes only when chap was its sole child.
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//!
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//! \a removedOffset and \a removedLength report what was cut, which the caller
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//! needs to locate atoms that sat after it.
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void removeAudioTref(TagLib::File *file, const MP4::Atoms *atoms,
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const MP4::Atom *audioTrak, offset_t &removedOffset,
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offset_t &removedLength)
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{
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removedOffset = -1;
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removedLength = 0;
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for(const auto &child : audioTrak->children()) {
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if(child->name() != "tref")
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continue;
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offset_t chapOff = 0;
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offset_t chapLen = 0;
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if(!findTrefEntry(file, child, "chap", chapOff, chapLen))
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continue;
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const offset_t trefOff = child->offset();
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const offset_t trefLen = child->length();
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file->removeBlock(trefOff, trefLen);
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// chap alone in the tref means the tref has nothing left to hold.
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const bool trefHoldsOnlyChap = (chapLen + 8 == trefLen);
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const offset_t cutOff = trefHoldsOnlyChap ? trefOff : chapOff;
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const offset_t cutLen = trefHoldsOnlyChap ? trefLen : chapLen;
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file->removeBlock(cutOff, cutLen);
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// Shrink the surviving tref. Its own offset precedes the cut, so it is
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// still where the atom tree says it is.
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if(!trefHoldsOnlyChap) {
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file->seek(trefOff);
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const unsigned int trefSize = file->readBlock(4).toUInt();
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file->seek(trefOff);
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file->writeBlock(ByteVector::fromUInt(
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static_cast<unsigned int>(trefSize - cutLen)));
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}
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// Fix audio trak size on disk
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file->seek(audioTrak->offset());
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const unsigned int trakSize = file->readBlock(4).toUInt();
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file->seek(audioTrak->offset());
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file->writeBlock(ByteVector::fromUInt(
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static_cast<unsigned int>(trakSize - trefLen)));
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static_cast<unsigned int>(trakSize - cutLen)));
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const MP4::AtomList moovPath = atoms->path("moov");
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updateParentSizes(file, moovPath, -trefLen);
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updateChunkOffsets(file, atoms, -trefLen, trefOff);
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updateParentSizes(file, moovPath, -cutLen);
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updateChunkOffsets(file, atoms, -cutLen, cutOff);
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removedOffset = cutOff;
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removedLength = cutLen;
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return;
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}
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}
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@@ -1042,17 +1133,6 @@ namespace
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}
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}
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// Capture tref/chapter trak locations for mdat offset fix-up below.
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offset_t trefOff = -1;
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offset_t trefLen = 0;
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for(const auto &child : audioTrak->children()) {
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if(child->name() == "tref") {
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trefOff = child->offset();
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trefLen = child->length();
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break;
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}
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}
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// Remove chapter trak FIRST (higher offset in file).
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const offset_t chapterOff = chapterTrak->offset();
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const offset_t chapterLen = chapterTrak->length();
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@@ -1067,8 +1147,11 @@ namespace
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updateParentSizes(file, moovPath, -chapterLen);
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updateChunkOffsets(file, atoms, -chapterLen, chapterOff);
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// Remove tref from audio trak (lower offset, still valid after chapter trak removal).
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removeAudioTref(file, atoms, audioTrak);
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// Remove the chapter reference from the audio trak (lower offset, still valid
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// after chapter trak removal). Only the chap box goes when the tref is shared.
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offset_t trefOff = -1;
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offset_t trefLen = 0;
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removeAudioTref(file, atoms, audioTrak, trefOff, trefLen);
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// Decide whether the chapter mdat is safe to delete.
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if(chapterMdatOffset < 0)
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@@ -1236,14 +1319,21 @@ bool MP4::QtChapterList::write(TagLib::File *file)
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constexpr unsigned int timescale = 1000;
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const std::vector<unsigned int> sampleSizes = calculateSampleSizes(workingChapters);
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// Build tref/chap atom for audio track
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const ByteVector trefAtom = buildTref(chapterTrackId);
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// The chapter reference joins the audio track's existing tref when it has one --
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// a second tref in the same trak makes AVFoundation discard the entire track,
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// silently, while more permissive parsers still read it.
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const Atom *existingTref = findTrefAtom(audio.trak);
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const ByteVector refPayload = existingTref ? buildChap(chapterTrackId)
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: buildTref(chapterTrackId);
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const offset_t refInsertOffset = existingTref
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? existingTref->offset() + existingTref->length()
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: audio.trak->offset() + audio.trak->length();
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// Two-pass build for chapter trak: first to measure size, then with correct stco offsets.
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const ByteVector trakMeasure = buildChapterTrak(
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chapterTrackId, timescale, durationMs, workingChapters, sampleSizes, 0,
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movieInfo.duration);
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const auto totalInsert = static_cast<offset_t>(trefAtom.size() + trakMeasure.size());
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const auto totalInsert = static_cast<offset_t>(refPayload.size() + trakMeasure.size());
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// Text samples go inside an mdat atom at EOF. stco offsets point past the 8-byte mdat header.
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const offset_t textDataOffset = file->length() + totalInsert + 8;
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@@ -1252,30 +1342,41 @@ bool MP4::QtChapterList::write(TagLib::File *file)
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chapterTrackId, timescale, durationMs, workingChapters, sampleSizes, textDataOffset,
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movieInfo.duration);
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// Combined payload: tref (goes inside audio trak) + chapter trak (moov sibling)
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ByteVector combinedPayload = trefAtom;
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combinedPayload.append(trakAtom);
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// The chapter trak is a moov sibling placed after the audio trak; the reference
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// goes inside the audio trak, at or before that boundary. Insert the higher offset
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// first so the lower one is still where the atom tree says it is.
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const offset_t trakInsertOffset = audio.trak->offset() + audio.trak->length();
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// Insert at the end of the audio trak boundary.
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// tref is logically inside audio trak; chapter trak is logically after it.
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const offset_t insertOffset = audio.trak->offset() + audio.trak->length();
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// The atom tree is corrected once per insertion, because each shifts only what
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// follows it. A single combined delta would move the stco atoms lying between the
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// two -- the audio track's own -- further than the file actually moved them, and
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// the next seek would write chunk offsets into the following trak.
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file->insert(trakAtom, trakInsertOffset, 0);
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updateChunkOffsets(file, activeAtoms, static_cast<offset_t>(trakAtom.size()),
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trakInsertOffset);
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file->insert(combinedPayload, insertOffset, 0);
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file->insert(refPayload, refInsertOffset, 0);
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updateChunkOffsets(file, activeAtoms, static_cast<offset_t>(refPayload.size()),
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refInsertOffset);
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// Fix audio trak size on disk -- only tref goes inside
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// Grow the shared tref by the chap box it now carries.
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if(existingTref) {
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file->seek(existingTref->offset());
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const unsigned int trefSize = file->readBlock(4).toUInt();
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file->seek(existingTref->offset());
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file->writeBlock(ByteVector::fromUInt(trefSize + refPayload.size()));
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}
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// Fix audio trak size on disk -- only the reference goes inside
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file->seek(audio.trak->offset());
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const unsigned int audioTrakSize = file->readBlock(4).toUInt();
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const unsigned int newAudioTrakSize = audioTrakSize + trefAtom.size();
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const unsigned int newAudioTrakSize = audioTrakSize + refPayload.size();
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file->seek(audio.trak->offset());
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file->writeBlock(ByteVector::fromUInt(newAudioTrakSize));
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// Fix moov size -- both tref and chapter trak are inside moov
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// Fix moov size -- both the reference and the chapter trak are inside moov
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const AtomList moovPath = activeAtoms->path("moov");
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updateParentSizes(file, moovPath, combinedPayload.size());
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// Fix existing chunk offsets -- only the ORIGINAL atom tree is iterated,
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// so the new chapter trak's stco (which already has correct offsets) is untouched.
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updateChunkOffsets(file, activeAtoms, combinedPayload.size(), insertOffset);
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updateParentSizes(file, moovPath, totalInsert);
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// ---- Phase 4: Append text samples in mdat at EOF ----
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@@ -1290,7 +1391,7 @@ bool MP4::QtChapterList::write(TagLib::File *file)
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file->writeBlock(mdatAtom);
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// ---- Phase 5: Update mvhd next_track_ID ----
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// mvhd is before insertOffset, so its offset is unchanged.
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// mvhd precedes both insertions, so its offset is unchanged.
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if(const unsigned int currentNextId = getNextTrackId(file, activeAtoms);
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chapterTrackId >= currentNextId) {
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+124
-1
@@ -170,6 +170,7 @@ class TestMP4 : public CppUnit::TestFixture
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CPPUNIT_TEST(testQTChapterListTimestampPrecision);
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CPPUNIT_TEST(testQTChapterListNonZeroFirstChapter);
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CPPUNIT_TEST(testQTChapterListNoOrphanedMdat);
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CPPUNIT_TEST(testQTChapterListSharedTref);
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CPPUNIT_TEST(testQTChapterListSharedMdatPreservesAudio);
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CPPUNIT_TEST(testQTChapterListUnicodeTitles);
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CPPUNIT_TEST(testChapterListUnicodeTitles);
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@@ -1438,6 +1439,128 @@ public:
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CPPUNIT_ASSERT_EQUAL(baseMdatTagLib, countMdatTagLib());
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}
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// A trak may hold at most one tref, so a chapter reference has to join the atom
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// already there rather than add a second one. Parsers differ on a track carrying
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// two: the lenient ones ignore the surplus atom, the strict ones discard the whole
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// track rather than just the reference. The file therefore still reads correctly
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// here while presenting as having no audio elsewhere, and a remux driven by such a
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// parser writes that loss back to disk.
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//
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// A pre-existing tref is usual in camera recordings, whose audio track references
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// a timecode track. No file in tests/data carries one, so it is injected here.
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void testQTChapterListSharedTref()
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{
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ScopedFileCopy copy("no-tags", ".m4a");
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string filename = copy.fileName();
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// The reference types inside each tref of the first audio trak, grouped per
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// tref so that two atoms are distinguishable from one merged atom.
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auto audioTrefs = [&]() {
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std::vector<std::vector<String>> result;
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PlainFile pf(filename.c_str());
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MP4::Atoms atoms(&pf);
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MP4::Atom *moov = atoms.find("moov");
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if(!moov)
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return result;
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for(auto *trak : moov->findall("trak")) {
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const MP4::Atom *hdlr = trak->find("mdia", "hdlr");
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if(!hdlr)
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continue;
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pf.seek(hdlr->offset());
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if(!pf.readBlock(hdlr->length()).containsAt("soun", 16))
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continue;
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for(const auto *child : trak->children()) {
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if(child->name() != "tref")
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continue;
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std::vector<String> refs;
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const offset_t trefEnd = child->offset() + child->length();
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pf.seek(child->offset() + 8);
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while(pf.tell() + 8 <= trefEnd) {
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const offset_t boxStart = pf.tell();
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const ByteVector header = pf.readBlock(8);
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if(header.size() < 8)
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break;
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const unsigned int boxSize = header.toUInt();
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if(boxSize < 8)
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break;
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refs.push_back(String(header.mid(4, 4)));
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pf.seek(boxStart + boxSize);
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}
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result.push_back(refs);
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}
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break;
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}
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return result;
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};
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// Give the audio track a timecode reference of its own. moov follows mdat in
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// this file, so the insertion shifts no chunk offset.
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{
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PlainFile pf(filename.c_str());
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MP4::Atoms atoms(&pf);
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MP4::Atom *moov = atoms.find("moov");
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CPPUNIT_ASSERT(moov);
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const MP4::AtomList traks = moov->findall("trak");
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CPPUNIT_ASSERT(!traks.isEmpty());
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const MP4::Atom *trak = traks.front();
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const ByteVector tmcd = ByteVector::fromUInt(12) + ByteVector("tmcd") +
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ByteVector::fromUInt(3);
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const ByteVector tref = ByteVector::fromUInt(8 + tmcd.size()) +
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ByteVector("tref") + tmcd;
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pf.insert(tref, trak->offset() + trak->length(), 0);
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pf.seek(trak->offset());
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const unsigned int trakSize = pf.readBlock(4).toUInt();
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pf.seek(trak->offset());
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pf.writeBlock(ByteVector::fromUInt(trakSize + tref.size()));
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pf.seek(moov->offset());
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const unsigned int moovSize = pf.readBlock(4).toUInt();
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pf.seek(moov->offset());
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pf.writeBlock(ByteVector::fromUInt(moovSize + tref.size()));
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}
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const std::vector<std::vector<String>> before = audioTrefs();
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CPPUNIT_ASSERT_EQUAL(static_cast<size_t>(1), before.size());
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CPPUNIT_ASSERT_EQUAL(static_cast<size_t>(1), before[0].size());
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CPPUNIT_ASSERT_EQUAL(String("tmcd"), before[0][0]);
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{
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MP4::File f(filename.c_str());
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f.setQtChapters(MP4::ChapterList{
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MP4::Chapter("Chapter 1", 0),
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MP4::Chapter("Chapter 2", 10000LL)
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});
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CPPUNIT_ASSERT(f.save());
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}
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// One tref still, now carrying both references.
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const std::vector<std::vector<String>> written = audioTrefs();
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CPPUNIT_ASSERT_EQUAL(static_cast<size_t>(1), written.size());
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CPPUNIT_ASSERT_EQUAL(static_cast<size_t>(2), written[0].size());
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CPPUNIT_ASSERT_EQUAL(String("tmcd"), written[0][0]);
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CPPUNIT_ASSERT_EQUAL(String("chap"), written[0][1]);
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{
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MP4::File f(filename.c_str());
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CPPUNIT_ASSERT_EQUAL(static_cast<unsigned int>(2), f.qtChapters().size());
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f.setQtChapters(MP4::ChapterList());
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CPPUNIT_ASSERT(f.save());
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}
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// Removal takes the chapter reference back out and leaves the timecode one.
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const std::vector<std::vector<String>> removed = audioTrefs();
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CPPUNIT_ASSERT_EQUAL(static_cast<size_t>(1), removed.size());
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CPPUNIT_ASSERT_EQUAL(static_cast<size_t>(1), removed[0].size());
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CPPUNIT_ASSERT_EQUAL(String("tmcd"), removed[0][0]);
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}
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// Regression test for the data-loss bug reported in PR #1343 by ufleisch.
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// Audiobook-style files co-locate chapter text samples inside the main
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// audio mdat. In that case the chapter track's stco[0] does NOT mark a
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@@ -1493,7 +1616,7 @@ public:
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{
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PlainFile pf(filename.c_str());
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MP4::Atoms atoms(&pf);
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const MP4::Atom *moov = atoms.find("moov");
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MP4::Atom *moov = atoms.find("moov");
|
||||
CPPUNIT_ASSERT(moov);
|
||||
const MP4::AtomList traks = moov->findall("trak");
|
||||
CPPUNIT_ASSERT(traks.size() >= 2);
|
||||
|
||||
Reference in New Issue
Block a user