| // MPEG versions - use [version] const uint8_t mpeg_versions[4] = { 25, 0, 2, 1 };
// Layers - use [layer]
const uint8_t mpeg_layers[4] = { 0, 3, 2, 1 };
// Bitrates - use [version][layer][bitrate]
const uint16_t mpeg_bitrates[4][4][16] = {
{ // Version 2.5
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, // Reserved
{ 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0 }, // Layer 3
{ 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0 }, // Layer 2
{ 0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256, 0 } // Layer 1
},
{ // Reserved
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, // Invalid
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, // Invalid
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, // Invalid
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 } // Invalid
},
{ // Version 2
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, // Reserved
{ 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0 }, // Layer 3
{ 0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, 0 }, // Layer 2
{ 0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256, 0 } // Layer 1
},
{ // Version 1
{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, // Reserved
{ 0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 0 }, // Layer 3
{ 0, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384, 0 }, // Layer 2
{ 0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448, 0 }, // Layer 1
}
};
// Sample rates - use [version][srate]
const uint16_t mpeg_srates[4][4] = {
{ 11025, 12000, 8000, 0 }, // MPEG 2.5
{ 0, 0, 0, 0 }, // Reserved
{ 22050, 24000, 16000, 0 }, // MPEG 2
{ 44100, 48000, 32000, 0 } // MPEG 1
};
// Samples per frame - use [version][layer]
const uint16_t mpeg_frame_samples[4][4] = {
// Rsvd 3 2 1 < Layer v Version
{ 0, 576, 1152, 384 }, // 2.5
{ 0, 0, 0, 0 }, // Reserved
{ 0, 576, 1152, 384 }, // 2
{ 0, 1152, 1152, 384 } // 1
};
// Slot size (MPEG unit of measurement) - use [layer]
const uint8_t mpeg_slot_size[4] = { 0, 1, 1, 4 }; // Rsvd, 3, 2, 1
uint16_t mpg_get_frame_size (char *hdr) {
// Quick validity check
if ( ( ((unsigned char)hdr[0] & 0xFF) != 0xFF)
|| ( ((unsigned char)hdr[1] & 0xE0) != 0xE0) // 3 sync bits
|| ( ((unsigned char)hdr[1] & 0x18) == 0x08) // Version rsvd
|| ( ((unsigned char)hdr[1] & 0x06) == 0x00) // Layer rsvd
|| ( ((unsigned char)hdr[2] & 0xF0) == 0xF0) // Bitrate rsvd
) return 0;
// Data to be extracted from the header
uint8_t ver = (hdr[1] & 0x18) >> 3; // Version index
uint8_t lyr = (hdr[1] & 0x06) >> 1; // Layer index
uint8_t pad = (hdr[2] & 0x02) >> 1; // Padding? 0/1
uint8_t brx = (hdr[2] & 0xf0) >> 4; // Bitrate index
uint8_t srx = (hdr[2] & 0x0c) >> 2; // SampRate index
// Lookup real values of these fields
uint32_t bitrate = mpeg_bitrates[ver][lyr][brx] * 1000;
uint32_t samprate = mpeg_srates[ver][srx];
uint16_t samples = mpeg_frame_samples[ver][lyr];
uint8_t slot_size = mpeg_slot_size[lyr];
// In-between calculations
float bps = (float)samples / 8.0;
float fsize = ( (bps * (float)bitrate) / (float)samprate ) + ( (pad) ? slot_size : 0 );
// Frame sizes are truncated integers
return (uint16_t)fsize;
}
[링크 : http://www.hydrogenaud.io/forums/index.php?showtopic=85125] |
