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- #ifndef _mp3_header_h_
- #define _mp3_header_h_
-
- // https://en.wikipedia.org/wiki/MP3
-
- #if defined(__cplusplus)
- extern "C" {
- #endif
-
- /*
- ISO/IEC 11172-3
- 2.4.1.3 Header
- unsigned int sync: 12
- unsigned int version: 1
- unsigned int layer: 2
- unsigned int error protection: 1
- unsigned int bitrate_index: 4
- unsigned int sampling_frequency: 2
- unsigned int padding: 1
- unsigned int private: 1
- unsigned int mode: 2
- unsigned int mode extension: 2
- unsigned int copyright: 1
- unsigned int original: 1
- unsigned int emphasis: 2
-
- bit_rate_index Layer I Layer II Layer III
- '0000' free format free format free format
- '0001' 32 kbit/s 32 kbit/s 32 kbit/s
- '0010' 64 kbit/s 48 kbit/s 40 kbit/s
- '0011' 96 kbit/s 56 kbit/s 48 kbit/s
- '0100' 128 kbit/s 64 kbit/s 56 kbit/s
- '0101' 160 kbit/s 80 kbit/s 64 kbit/s
- '0110' 192 kbit/s 96 kbit/s 80 kbit/s
- '0111' 224 kbit/s 112 kbit/s 96 kbit/s
- '1000' 256 kbit/s 128 kbit/s 112 kbit/s
- '1001' 288 kbit/s 160 kbit/s 128 kbit/s
- '1010' 320 kbit/s 192 kbit/s 160 kbit/s
- '1011' 352 kbit/s 224 kbit/s 192 kbit/s
- '1100' 384 kbit/s 256 kbit/s 224 kbit/s
- '1101' 416 kbit/s 320 kbit/s 256 kbit/s
- '1110' 448 kbit/s 384 kbit/s 320 kbit/s
-
- sampling_frequency
- '00' 44.1 kHz
- '01' 48 kHz
- '10' 32 kHz
- '11' reserved
-
- mode
- '00' stereo
- '01' joint_stereo (intensity_stereo and/or ms_stereo)
- '10' dual_channel
- '11' single_channel
-
- mode_extension
- '00' subbands 4-31 in intensity_stereo, bound==4
- '01' subbands 8-31 in intensity_stereo, bound==8
- '10' subbands 12-31 in intensity_stereo, bound==12
- '11' subbands 16-31 in intensity_stereo, bound==16
-
- emphasis
- '00' no emphasis
- '01' 50/15 microsec. emphasis
- '10' reserved
- '11' CCITT J.17
- */
-
- struct mp3_header_t
- {
- unsigned int version : 2; // 0-MPEG 2.5, 1-undefined, 2-MPEG-2, 3-MPEG-1
- unsigned int layer : 2; // 3-Layer I, 2-Layer II, 1-Layer III, 0-reserved
- unsigned int protection : 1;
- unsigned int bitrate_index : 4; //0-free,
- unsigned int sampling_frequency : 2;
- unsigned int priviate : 1;
- unsigned int mode : 2;
- unsigned int mode_extension : 2;
- unsigned int copyright : 1;
- unsigned int original : 1;
- unsigned int emphasis : 2;
- };
-
- // version
- #define MP3_MPEG1 3
- #define MP3_MPEG2 2
- #define MP3_MPEG2_5 0
-
- // layer
- #define MP3_LAYER1 3
- #define MP3_LAYER2 2
- #define MP3_LAYER3 1
-
- #define MP3_BITS_PER_SAMPLE 16
-
- ///MP3 Header size: 4
- int mp3_header_load(struct mp3_header_t* mp3, const void* data, int bytes);
- int mp3_header_save(const struct mp3_header_t* mp3, void* data, int bytes);
-
- int mp3_get_channel(const struct mp3_header_t* mp3);
- int mp3_get_bitrate(const struct mp3_header_t* mp3);
- int mp3_set_bitrate(struct mp3_header_t* mp3, int bitrate);
- int mp3_get_frequency(const struct mp3_header_t* mp3);
- int mp3_set_frequency(struct mp3_header_t* mp3, int frequency);
-
- #if defined(__cplusplus)
- }
- #endif
- #endif /* !_mp3_header_h_ */
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