/*
Example: AAC, 1024 frames/packet, 2112 frame offset
2112
|
Absolute frames: 0 1024 2048 | 3072
+---------+---------+--|------+---------+---------+
Packets: | 0 | 1 | | 2 | 3 | 4 |
+---------+---------+--|------+---------+---------+
Client frames: -2112 -1088 -64 | 960 SeekToFrame, TellFrame
|
0
* Offset between absolute and client frames is mFrame0Offset.
*** mFrameMark is in client frames ***
Examples:
clientFrame 0 960 1000 1024
absoluteFrame 2112 3072 3112 3136
packet 0 0 0 1
tempFrameMark* -2112 -2112 -2112 -1088
mFramesToSkipFollowingSeek 2112 3072 3112 2112
*/
void CAAudioFile::Seek(SInt64 clientFrame)
{
if (clientFrame == mFrameMark)
return; // already there! don't reset converter
//SInt64 absoluteFrame = clientFrame + mFrame0Offset;
XThrowIf(mMode != kReading || clientFrame < 0 || !mClientDataFormat.IsPCM(), kExtAudioFileError_InvalidSeek, "seek to frame in audio file");
#if VERBOSE_IO
SInt64 prevFrameMark = mFrameMark;
#endif
SInt64 packet;
packet = FrameToPacket(clientFrame);
if (packet < 0)
packet = 0;
SeekToPacket(packet);
// this will have backed up mFrameMark to match the beginning of the packet
mFramesToSkipFollowingSeek = std::max(UInt32(clientFrame - mFrameMark), UInt32(0));
mFrameMark = clientFrame;
#if VERBOSE_IO
printf("CAAudioFile::SeekToFrame: frame %qd (from %qd), packet %qd, skip %ld frames\n", mFrameMark, prevFrameMark, packet, mFramesToSkipFollowingSeek);
#endif
}
// ////////////////////////////////////////////////////////////////////////////
unsigned int PacketFileReader::GetPacketCount()
{
if (packet_count_is_known_)
return(packet_count_);
FileOffsetSaver saved_offset(*this);
unsigned long long packet_offset = packet_offset_;
unsigned int packet_count;
SeekToPacket(std::numeric_limits<unsigned int>::max(), packet_count);
packet_offset_ = packet_offset;
packet_count_ = packet_count;
packet_count_is_known_ = true;
return(packet_count);
}
// ////////////////////////////////////////////////////////////////////////////
bool PacketFileReader::SeekToPacket(unsigned int packet_index)
{
unsigned int packet_count;
return(SeekToPacket(packet_index, packet_count));
}