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Jef 2024-09-24 14:54:57 +02:00
parent 537bcbc862
commit fc06254474
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Src/external_dependencies/openmpt-trunk/soundlib/MPEGFrame.cpp Normal file
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/*
* MPEGFrame.cpp
* -------------
* Purpose: Basic MPEG frame parsing functionality
* Notes : (currently none)
* Authors: OpenMPT Devs
* The OpenMPT source code is released under the BSD license. Read LICENSE for more details.
*/
#include "stdafx.h"
#include "MPEGFrame.h"
#include "../common/FileReader.h"
OPENMPT_NAMESPACE_BEGIN
// Samples per frame - for each MPEG version and all three layers
static constexpr uint16 samplesPerFrame[2][3] =
{
{ 384, 1152, 1152 }, // MPEG 1
{ 384, 1152, 576 } // MPEG 2 / 2.5
};
// Bit rates for each MPEG version and all three layers
static constexpr uint16 bitRates[2][3][15] =
{
// MPEG 1
{
{ 0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448 }, // Layer 1
{ 0, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384 }, // Layer 2
{ 0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320 } // Layer 3
},
// MPEG 2 / 2.5
{
{ 0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256 }, // Layer 1
{ 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160 }, // Layer 2
{ 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160 } // Layer 3
}
};
// Sampling rates for each MPEG version and all three layers
static constexpr uint16 samplingRates[4][3] =
{
{ 11025, 12000, 8000 }, // MPEG 2.5
{ 0, 0, 0 }, // Invalid
{ 22050, 24000, 16000 }, // MPEG 2
{ 44100, 48000, 32000 } // MPEG 1
};
// Samples per Frame / 8
static constexpr uint8 mpegCoefficients[2][3] =
{
{ 12, 144, 144 }, // MPEG 1
{ 12, 144, 72 } // MPEG 2 / 2.5
};
// Side info size = Offset in frame where Xing/Info magic starts
static constexpr uint8 sideInfoSize[2][2] =
{
{ 17, 32 }, // MPEG 1
{ 9, 17 } // MPEG 2 / 2.5
};
bool MPEGFrame::IsMPEGHeader(const uint8 (&header)[3])
{
return header[0] == 0xFF && (header[1] & 0xE0) == 0xE0 // Sync
&& (header[1] & 0x18) != 0x08 // Invalid MPEG version
&& (header[1] & 0x06) != 0x00 // Invalid MPEG layer
&& (header[2] & 0x0C) != 0x0C // Invalid frequency
&& (header[2] & 0xF0) != 0xF0; // Invalid bitrate
}
MPEGFrame::MPEGFrame(FileReader &file)
: frameSize(0)
, numSamples(0)
, isValid(false)
, isLAME(false)
{
uint8 header[4];
file.ReadArray(header);
if(!IsMPEGHeader(reinterpret_cast<const uint8(&)[3]>(header)))
return;
uint8 version = (header[1] & 0x18) >> 3;
uint8 mpeg1 = (version == 3) ? 0 : 1;
uint8 layer = 3 - ((header[1] & 0x06) >> 1);
uint8 bitRate = (header[2] & 0xF0) >> 4;
uint8 sampleRate = (header[2] & 0x0C) >> 2;
uint8 padding = (header[2] & 0x02) >> 1;
bool stereo = ((header[3] & 0xC0) >> 6) != 3;
isValid = true;
frameSize = (((mpegCoefficients[mpeg1][layer] * (bitRates[mpeg1][layer][bitRate] * 1000) / samplingRates[version][sampleRate]) + padding)) * (layer == 0 ? 4 : 1);
numSamples = samplesPerFrame[mpeg1][layer];
if(stereo) numSamples *= 2u;
uint32 lameOffset = sideInfoSize[mpeg1][stereo ? 1 : 0];
if(frameSize < lameOffset + 8)
return;
uint8 frame[36];
file.ReadStructPartial(frame, lameOffset + 4);
// Don't check first two bytes, might be CRC
for(uint32 i = 2; i < lameOffset; i++)
{
if(frame[i] != 0)
return;
}
// This is all we really need to know for our purposes in the MO3 decoder.
isLAME = !memcmp(frame + lameOffset, "Info", 4) || !memcmp(frame + lameOffset, "Xing", 4);
}
OPENMPT_NAMESPACE_END