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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>Speex Programming</title>
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content="text/html; charset=ISO-8859-1">
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<div align="center">
<h1>Speex Programming</h1>
<div align="left">
<h2>Encoding</h2>
In order to encode speech using Speex, you first need to:<br>
<blockquote>
<pre><big>#include <speex.h></big></pre>
</blockquote>
You then need to declare a Speex bit-packing struct<br>
<blockquote>
<pre><big>SpeexBits bits;</big></pre>
</blockquote>
and a Speex encoder state<br>
<blockquote>
<pre><big>void *enc_state;</big></pre>
</blockquote>
The two are initialized by:<br>
<blockquote>
<pre><big>speex_bits_init(&bits);</big></pre>
<pre><big>enc_state = speex_encoder_init(&speex_nb_mode);</big></pre>
</blockquote>
For wideband coding, <i>speex_nb_mode</i> will be replaced by <i>speex_wb_mode</i>
. In most cases, you will need to know the frame size used by the mode you
are using. You can get that value in the <i>frame_size</i> variable with:<br>
<blockquote><big><tt>speex_encoder_ctl(enc_state, SPEEX_GET_FRAME_SIZE, &frame_size);</tt></big><br>
</blockquote>
For every input frame:<br>
<blockquote>
<pre><big>speex_bits_reset(&bits);</big></pre>
<pre><big>speex_encode(enc_state, input_frame, &bits);</big></pre>
<pre><big>nbBytes = speex_bits_write(&bits, byte_ptr, MAX_NB_BYTES);</big></pre>
</blockquote>
where <i>input_frame</i> is a <i>(float *)</i> pointing to the beginning
of a speech frame, byte_ptr is a <i>(char *)</i> where the encoded frame will
be written, <i>MAX_NB_BYTES</i> is the maximum number of bytes that can be
written to <i>byte_ptr</i> without causing an overflow and <i>nbBytes</i>
is the number of bytes actually written to <i>byte_ptr</i> (the encoded
size in bytes).<br>
<br>
After you're done with the encoding, free all resources with:<br>
<blockquote>
<pre><big>speex_bits_destroy(&bits);</big></pre>
<pre><big>speex_encoder_destroy(&enc_state);</big></pre>
</blockquote>
That's about it for the encoder.<br>
<h2>Decoding</h2>
In order to encode speech using Speex, you first need to:<br>
<blockquote>
<pre><big>#include <speex.h></big></pre>
</blockquote>
You then need to declare a Speex bit-packing struct<br>
<blockquote>
<pre><big>SpeexBits bits;</big></pre>
</blockquote>
and a Speex encoder state<br>
<blockquote>
<pre><big>void *dec_state;</big></pre>
</blockquote>
The two are initialized by:<br>
<blockquote>
<pre><big>speex_bits_init(&bits);</big></pre>
<pre><big>dec_state = speex_decoder_init(&speex_nb_mode);</big></pre>
</blockquote>
For wideband decoding, <i>speex_nb_mode</i> will be replaced by <i>speex_wb_mode</i>
. You can get that value in the <i>frame_size</i> variable with:<br>
<blockquote><big><tt>speex_decoder_ctl(dec_state, SPEEX_GET_FRAME_SIZE, &frame_size);</tt></big><br>
</blockquote>
There is also a parameter that can be set for the decoder: whether or not
to use a perceptual post-filter. This can be set by:<br>
<blockquote><big><tt>speex_decoder_ctl(dec_state, SPEEX_SET_PF, &pf);</tt></big><br>
</blockquote>
where <i>pf</i> is an <i>int</i> that with value 0 to have the post-filter
disabled and 1 to have it enabled.<br>
<br>
For every input frame:<br>
<blockquote>
<pre><big>speex_bits_read_from(&bits, input_bytes, nbBytes);</big></pre>
<pre><big>speex_decode(st, &bits, output_frame, 0);</big></pre>
</blockquote>
where <i>input_bytes</i> is a <i>(char *)</i> containing the bit-stream
data received for a frame, <i>nbBytes</i> is the size (in bytes) of that
bit-stream, and <i>output_frame</i> is a <i>(float *)</i> and points to the
area where the decoded speech frame will be written. The last argument indicates
whether the frame we'd like to decode was lost. A value of 0 indicates the
normal case where bits points to the bit of the current frame. A value of
1 indicates that we don't have the bits for the current frame, in which case
the bits argument should be the same as the bits for the last correctly received
frame. When a frame is lost, the Speex decoder will do its best to "guess"
the sorrect signal.<br>
<br>
</div>
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