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https://github.com/cookiengineer/audacity
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82 lines
2.7 KiB
Plaintext
82 lines
2.7 KiB
Plaintext
The libtwolame API
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==================
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This is the interface for encoding PCM audio to MPEG Audio Layer 2.
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It is 'very' similar to the libmp3lame API.
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See simplefrontend/simplefrontend.c for a very simple application
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using the API.
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Steps to encode PCM to MP2
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--------------------------
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1. Grab a set of default options by calling:
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twolame_options *encodeOptions;
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encodeOptions = twolame_init();
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2. Adjust those options to suit your requirements.
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See twolame.h for a full list of options. eg.
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twolame_set_out_samplerate(encodeOptions, 32000);
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twolame_set_bitrate(encodeOptions, 160);
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3. Initialise twolame library with these options by calling:
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twolame_init_params(encodeOptions);
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NOTE: The return value should be checked to see if the options were valid.
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Currently only ever returns 0
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4. Encode PCM audio to MP2 by calling:
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int twolame_encode_buffer(
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twolame_options *glopts, // the set of options you're using
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const short int leftpcm[], // the left and right audio channels
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const short int rightpcm[],
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int num_samples, // the number of samples in each channel
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unsigned char *mp2buffer, // a pointer to a buffer for the MP2 audio data
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// NB User must allocate space!
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int mp2buffer_size); // The size of the mp2buffer that the user allocated
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int *mp2fill_size);
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This function returns the number of bytes written into mp2buffer by the library MPEG.
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One frame of MPEG audio will be returned for every 1152 samples of PCM audio.
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Multiple calls can be made to this function.
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It is the users responsibility to:
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- allocate the mp2buffer
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- read the pcmaudio from somewhere with new samples always staring from
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the beginning of the buffer
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- write the mp2buffer contents to somewhere (it is overwritten with each call)
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5. Flush the encoder by calling:
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int twolame_encode_flush(
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twolame_options *glopts,
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unsigned char *mp2buffer,
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int mp2buffer_size);
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When encoding is finished, unless there was exactly a multiple of 1152 samples/channel
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sent to the encoder, there will be some remaining audio that is not encoded. This function
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encodes this last bit of audio by padding out with zeros until there is 1152 samples per channel
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in the PCM audio buffers and then encoding this.
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This function returns the number of bytes written into mp2buffer by the library MPEG.
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6. The user must "de-initialise" the encoder at the end by calling:
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void twolame_close(twolame_options **glopts);
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This function must be called to free all the memory and structures
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associated with this set of encoding parameters.
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POST: glopts = NULL
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