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| <h1>Speex Programming</h1> |
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| <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> |
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