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