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A bit more tolerant check for the MPEG frame length.

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This commit is contained in:
Tsuda Kageyu 2015-12-22 20:11:26 +09:00
parent 22708a0af6
commit 4064b34eff
4 changed files with 34 additions and 22 deletions
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30
taglib/mpeg/mpegheader.cpp
View File

@ -74,10 +74,10 @@ MPEG::Header::Header(const ByteVector &data) :
debug("MPEG::Header::Header() - This constructor is no longer used.");
}
MPEG::Header::Header(File *file, long offset) :
MPEG::Header::Header(File *file, long offset, bool checkLength) :
d(new HeaderPrivate())
{
parse(file, offset);
parse(file, offset, checkLength);
}
MPEG::Header::Header(const Header &h) :
@ -169,7 +169,7 @@ MPEG::Header &MPEG::Header::operator=(const Header &h)
// private members
////////////////////////////////////////////////////////////////////////////////
void MPEG::Header::parse(File *file, long offset)
void MPEG::Header::parse(File *file, long offset, bool checkLength)
{
file->seek(offset);
const ByteVector data = file->readBlock(4);
@ -301,12 +301,26 @@ void MPEG::Header::parse(File *file, long offset)
// Check if the frame length has been calculated correctly, or the next frame
// synch bytes are right next to the end of this frame.
file->seek(offset + d->frameLength);
const ByteVector nextSynch = file->readBlock(2);
// We read some extra bytes to be a bit tolerant.
if(nextSynch.size() < 2 || !firstSyncByte(nextSynch[0]) || !secondSynchByte(nextSynch[1])) {
debug("MPEG::Header::parse() -- Calculated frame length did not match the actual length.");
return;
if(checkLength) {
bool nextFrameFound = false;
file->seek(offset + d->frameLength);
const ByteVector nextSynch = file->readBlock(4);
for(int i = 0; i < static_cast<int>(nextSynch.size()) - 1; ++i) {
if(firstSyncByte(nextSynch[0]) && secondSynchByte(nextSynch[1])) {
nextFrameFound = true;
break;
}
}
if(!nextFrameFound) {
debug("MPEG::Header::parse() -- Calculated frame length did not match the actual length.");
return;
}
}
// Now that we're done parsing, set this to be a valid frame.

8
taglib/mpeg/mpegheader.h
View File

@ -56,8 +56,12 @@ namespace TagLib {
/*!
* Parses an MPEG header based on \a file and \a offset.
*
* \note If \a checkLength is true, this requires the next MPEG frame to
* check if the frame length is parsed and calculated correctly. So it's
* suitable for seeking for the first valid frame.
*/
Header(File *file, long offset);
Header(File *file, long offset, bool checkLength = true);
/*!
* Does a shallow copy of \a h.
@ -163,7 +167,7 @@ namespace TagLib {
Header &operator=(const Header &h);
private:
void parse(File *file, long offset);
void parse(File *file, long offset, bool checkLength);
class HeaderPrivate;
HeaderPrivate *d;

9
taglib/mpeg/mpegproperties.cpp
View File

@ -207,16 +207,13 @@ void MPEG::Properties::read(File *file)
// Look for the last MPEG audio frame to calculate the stream length.
// This actually finds the second last valid frame, since MPEG::Header requires
// the next frame header to check if the frame length is calculated correctly.
long lastFrameOffset = file->lastFrameOffset();
if(lastFrameOffset < 0) {
debug("MPEG::Properties::read() -- Could not find an MPEG frame in the stream.");
return;
}
Header lastHeader(file, lastFrameOffset);
Header lastHeader(file, lastFrameOffset, false);
while(!lastHeader.isValid()) {
lastFrameOffset = file->previousFrameOffset(lastFrameOffset);
@ -225,10 +222,10 @@ void MPEG::Properties::read(File *file)
return;
}
lastHeader = Header(file, lastFrameOffset);
lastHeader = Header(file, lastFrameOffset, false);
}
const long streamLength = lastFrameOffset - firstFrameOffset + lastHeader.frameLength() * 2;
const long streamLength = lastFrameOffset - firstFrameOffset + lastHeader.frameLength();
if(streamLength > 0)
d->length = static_cast<int>(streamLength * 8.0 / d->bitrate + 0.5);
}

9
tests/test_mpeg.cpp
View File

@ -93,18 +93,15 @@ public:
CPPUNIT_ASSERT_EQUAL(44100, f.audioProperties()->sampleRate());
CPPUNIT_ASSERT(!f.audioProperties()->xingHeader());
// This actually finds the second last valid frame, since MPEG::Header requires
// the next frame header to check if the frame length is calculated correctly.
long last = f.lastFrameOffset();
MPEG::Header lastHeader(&f, last);
MPEG::Header lastHeader(&f, last, false);
while(!lastHeader.isValid()) {
last = f.previousFrameOffset(last);
lastHeader = MPEG::Header(&f, last);
lastHeader = MPEG::Header(&f, last, false);
}
CPPUNIT_ASSERT_EQUAL(28004L, last);
CPPUNIT_ASSERT_EQUAL(28213L, last);
CPPUNIT_ASSERT_EQUAL(209, lastHeader.frameLength());
}