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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
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<title>The libtwolame API</title>
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<body class="article">
<div id="header">
<h1>The libtwolame API</h1>
<span id="revnumber">version 0.3.13</span>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph"><p>This is the interface for encoding PCM audio to MPEG Audio Layer 2.</p></div>
<div class="paragraph"><p>It is <em>very</em> similar to the libmp3lame API.</p></div>
<div class="paragraph"><p>See simplefrontend/simplefrontend.c for a very simple application
using the API.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_steps_to_encode_pcm_to_mp2">Steps to encode PCM to MP2</h2>
<div class="sectionbody">
<div class="olist arabic"><ol class="arabic">
<li>
<p>
Grab a set of default options by calling:
</p>
<div class="literalblock">
<div class="content">
<pre><tt>twolame_options *encodeOptions;
encodeOptions = twolame_init();</tt></pre>
</div></div>
</li>
<li>
<p>
Adjust those options to suit your requirements.
   See twolame.h for a full list of options. eg.
</p>
<div class="literalblock">
<div class="content">
<pre><tt>twolame_set_out_samplerate(encodeOptions, 32000);
twolame_set_bitrate(encodeOptions, 160);</tt></pre>
</div></div>
</li>
<li>
<p>
Initialise twolame library with these options by calling:
</p>
<div class="literalblock">
<div class="content">
<pre><tt>twolame_init_params(encodeOptions);</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>NOTE: The return value should be checked to see if the options were valid.
Currently only ever returns 0</tt></pre>
</div></div>
</li>
<li>
<p>
Encode PCM audio to MP2 by calling:
</p>
<div class="literalblock">
<div class="content">
<pre><tt>int twolame_encode_buffer(
 twolame_options *glopts,   // the set of options you're using
 const short int leftpcm[], // the left and right audio channels
 const short int rightpcm[],
 int num_samples,           // the number of samples in each channel
 unsigned char *mp2buffer,  // a pointer to a buffer for the MP2 audio data
                            // NB User must allocate space!
 int mp2buffer_size);       // The size of the mp2buffer that the user allocated
 int *mp2fill_size);</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>This function returns the number of bytes written into mp2buffer by the library MPEG.
One frame of MPEG audio will be returned for every 1152 samples of PCM audio.
Multiple calls can be made to this function.
It is the users responsibility to:</tt></pre>
</div></div>
<div class="ulist"><ul>
<li>
<p>
allocate the mp2buffer
</p>
</li>
<li>
<p>
read the pcmaudio from somewhere with new samples always staring from
           the beginning of the buffer
</p>
</li>
<li>
<p>
write the mp2buffer contents to somewhere (it is overwritten with each call)
</p>
</li>
</ul></div>
</li>
<li>
<p>
Flush the encoder by calling:
</p>
<div class="literalblock">
<div class="content">
<pre><tt>int twolame_encode_flush(
    twolame_options *glopts,
    unsigned char *mp2buffer,
    int mp2buffer_size);</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>When encoding is finished, unless there was exactly a multiple of 1152 samples/channel
sent to the encoder, there will be some remaining audio that is not encoded. This function
encodes this last bit of audio by padding out with zeros until there is 1152 samples per channel
in the PCM audio buffers and then encoding this.</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>This function returns the number of bytes written into mp2buffer by the library MPEG.</tt></pre>
</div></div>
</li>
<li>
<p>
The user must "de-initialise" the encoder at the end by calling:
</p>
<div class="literalblock">
<div class="content">
<pre><tt>void twolame_close(twolame_options **glopts);</tt></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><tt>This function must be called to free all the memory and structures
associated with this set of encoding parameters.
POST: glopts = NULL</tt></pre>
</div></div>
</li>
</ol></div>
</div>
</div>
</div>
<div id="footnotes"><hr /></div>
<div id="footer">
<div id="footer-text">
Version 0.3.13<br />
Last updated 2011-01-01 19:15:01 GMT
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