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