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#include "MPEGHeader.h"
#include <math.h>
// [mpeg_version][layer][index]
static const int bitrates[4][4][15] =
{
{
// MPEG-2.5
{ 0,},
{ 0, 8000, 16000, 24000, 32000, 40000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 144000, 160000}, // Layer 3
{ 0, 8000, 16000, 24000, 32000, 40000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 144000, 160000}, // Layer 2
{ 0, 32000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 144000, 160000, 176000, 192000, 224000, 256000}, // Layer 1
},
{
// invalid
{ 0, },
{ 0, },
{ 0, },
{ 0, },
},
{
// MPEG-2
{ 0,},
{ 0, 8000, 16000, 24000, 32000, 40000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 144000, 160000}, // Layer 3
{ 0, 8000, 16000, 24000, 32000, 40000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 144000, 160000}, // Layer 2
{ 0, 32000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 144000, 160000, 176000, 192000, 224000, 256000}, // Layer 1
},
{
// MPEG-1
{ 0,},
{ 0, 32000, 40000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 160000, 192000, 224000, 256000, 320000}, // Layer 3
{ 0, 32000, 48000, 56000, 64000, 80000, 96000, 112000, 128000, 160000, 192000, 224000, 256000, 320000, 384000}, // Layer 2
{ 0, 32000, 64000, 96000, 128000, 160000, 192000, 224000, 256000, 288000, 320000, 352000, 384000, 416000, 448000}, // Layer 1
},
};
// [mpeg_version][index]
static const int sample_rates[4][4] =
{
{11025, 12000, 8000, 0}, // MPEG-2.5
{0, },
{22050, 24000, 16000, 0}, // MPEG-2
{44100, 48000, 32000, 0}, // MPEG-1
};
// [mpeg_version][layer]
static const int samples_per_frame[4][4] =
{
// Layer 3, Layer 2, Layer 1
{ 0, 576, 1152, 384}, // MPEG2.5
{ 0, },
{ 0, 576, 1152, 384}, // MPEG2
{ 0, 1152, 1152, 384}, // MPEG1
};
// [layer]
static const int bits_per_slot[4] = { 0, 8, 8, 32 };
void MPEGHeader::ReadBuffer(const uint8_t *buffer)
{
sync = ((uint16_t)buffer[0] << 3) | (buffer[1] >> 5);
mpeg_version = (buffer[1] >> 3) & 3;
layer = (buffer[1] >> 1) & 3;
protection = (buffer[1]) & 1;
bitrate_index = (buffer[2] >> 4) & 0xF;
sample_rate_index = (buffer[2] >> 2) & 3;
padding_bit = (buffer[2] >> 1) & 1;
private_bit = buffer[2] & 1;
channel_mode = (buffer[3] >> 6) & 3;
mode_extension = (buffer[3] >> 4) & 3;
copyright = (buffer[3] >> 3) & 1;
original = (buffer[3] >> 2) & 1;
emphasis = (buffer[3]) & 3;
}
bool MPEGHeader::IsSync() const
{
return sync == 0x07FF
&& layer != LayerError
&& mpeg_version != MPEG_Error
&& bitrate_index != 15
&& bitrate_index != 0
&& sample_rate_index != 3
&& !(mpeg_version == MPEG2 && layer != Layer3)
&& !(mpeg_version == MPEG2_5 && layer != Layer3);
}
int MPEGHeader::GetBitrate() const
{
return bitrates[mpeg_version][layer][bitrate_index];
}
int MPEGHeader::HeaderSize() const
{
if (protection == CRC)
return 4 + 2; // 32bits frame header, 16bits CRC
else
return 4; // 32bits frame ehader
}
int MPEGHeader::GetSampleRate() const
{
return sample_rates[mpeg_version][sample_rate_index];
}
bool MPEGHeader::IsCopyright() const
{
return copyright == 1;
}
bool MPEGHeader::IsCRC() const
{
return protection == CRC;
}
bool MPEGHeader::IsOriginal() const
{
return original == 1;
}
int MPEGHeader::GetSamplesPerFrame() const
{
return samples_per_frame[mpeg_version][layer];
}
int MPEGHeader::FrameSize() const
{
int nBitsPerSlot;
int nAvgSlotsPerFrame;
nBitsPerSlot = bits_per_slot[layer];
nAvgSlotsPerFrame = (GetSamplesPerFrame() * (bitrates[mpeg_version][layer][bitrate_index] / nBitsPerSlot)) / sample_rates[mpeg_version][sample_rate_index];
return (nAvgSlotsPerFrame + padding_bit) * nBitsPerSlot / 8;
}
int MPEGHeader::GetLayer() const
{
switch(layer)
{
case Layer1:
return 1;
case Layer2:
return 2;
case Layer3:
return 3;
default:
return 0;
}
}
int MPEGHeader::GetNumChannels() const
{
switch(channel_mode)
{
case Stereo:
return 2;
case JointStereo:
return 2;
case DualChannel:
return 2;
case Mono:
return 1;
default:
return 0;
}
}
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