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1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> |
2 | <HTML> | |
3 | ||
4 | <HEAD> | |
5 | <TITLE> | |
6 | Secret Rabbit Code (aka libsamplerate) | |
7 | </TITLE> | |
8 | <META NAME="Author" CONTENT="Erik de Castro Lopo (erikd AT mega-nerd DOT com)"> | |
9 | <META NAME="Version" CONTENT="libsamplerate-0.1.8"> | |
10 | <META NAME="Description" CONTENT="The Secret Rabbit Code Home Page"> | |
11 | <META NAME="Keywords" CONTENT="libsamplerate sound resample audio dsp Linux"> | |
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15 | <BODY TEXT="#FFFFFF" BGCOLOR="#000000" LINK="#FB1465" VLINK="#FB1465" ALINK="#FB1465"> | |
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17 | <CENTER> | |
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20 | <!-- pepper --> | |
21 | <BR> | |
22 | <!-- pepper --> | |
23 | <TABLE ALIGN="center" WIDTH="98%"> | |
24 | <TR> | |
25 | <TD VALIGN="top"> | |
26 | <BR> | |
27 | <DIV CLASS="nav"> | |
28 | <BR> | |
29 | <A HREF="index.html">Home</A><BR> | |
30 | <BR> | |
31 | <A HREF="api_simple.html">Simple API</A><BR> | |
32 | <A HREF="api_full.html">Full API</A><BR> | |
33 | <A HREF="api_callback.html">Callback API</A><BR> | |
34 | <A HREF="api_misc.html">Miscellaneous</A><BR> | |
35 | <A HREF="api_misc.html#ErrorReporting">Error Handling</A><BR> | |
36 | <BR> | |
37 | <DIV CLASS="block"> | |
38 | Author :<BR>Erik de Castro Lopo | |
39 | <!-- pepper --> | |
40 | <BR><BR> | |
41 | <!-- pepper --> | |
42 | ||
43 | </DIV> | |
44 | <IMG SRC= | |
45 | "/cgi-bin/Count.cgi?ft=6|frgb=55;55;55|tr=0|md=6|dd=B|st=1|sh=1|df=src_api.dat" | |
46 | HEIGHT=30 WIDTH=100 ALT="counter.gif"> | |
47 | </DIV> | |
48 | ||
49 | </TD> | |
50 | <!-- pepper --> | |
51 | <!-- ######################################################################## --> | |
52 | <!-- pepper --> | |
53 | <TD VALIGN="top"> | |
54 | <DIV CLASS="block"> | |
55 | ||
56 | <H1><B>Callback API</B></H1> | |
57 | <P> | |
58 | The callback API consists of the following functions : | |
59 | </P> | |
60 | <PRE> | |
61 | typedef long (*src_callback_t) (void *cb_data, float **data) ; | |
62 | ||
63 | SRC_STATE* <A HREF="#Init">src_callback_new</A> (src_callback_t func, | |
64 | int converter_type, int channels, | |
65 | int *error, void* cb_data) ; | |
66 | ||
67 | SRC_STATE* <A HREF="api_full.html#CleanUp">src_delete</A> (SRC_STATE *state) ; | |
68 | ||
69 | long <A HREF="#Read">src_callback_read</A> (SRC_STATE *state, double src_ratio, | |
70 | long frames, float *data) ; | |
71 | ||
72 | int <A HREF="api_full.html#Reset">src_reset</A> (SRC_STATE *state) ; | |
73 | int <A HREF="api_full.html#SetRatio">src_set_ratio</A> (SRC_STATE *state, double new_ratio) ; | |
74 | </PRE> | |
75 | <BR> | |
76 | ||
77 | <P> | |
78 | Like the | |
79 | <A HREF="api_simple.html">simple API</a> | |
80 | and the | |
81 | <A HREF="api_full.html">full API</a>, | |
82 | the callback based API is able to operate on interleaved multi channel data. | |
83 | </P> | |
84 | ||
85 | <P> | |
86 | An example of the use of the callback based API can be found in the | |
87 | <B>varispeed-play</B> program in the <B>examples/</B> directory of the | |
88 | source code tarball. | |
89 | </P> | |
90 | ||
91 | <!-- pepper --> | |
92 | <A NAME="Init"></A> | |
93 | <H3><BR>Initialisation</H3> | |
94 | <PRE> | |
95 | SRC_STATE* src_callback_new (src_callback_t func, | |
96 | int converter_type, int channels, | |
97 | int *error, void* cb_data) ; | |
98 | </PRE> | |
99 | <P> | |
100 | The <B>src_callback_new</B> function returns an anonymous pointer to a | |
101 | sample rate converter callback object, src_state. | |
102 | This is the same type of object as that returned by <A HREF="api_full.html#init"> | |
103 | src_new</A>, but with different internal state. | |
104 | Although these are the same object type, they cannot be used interchangeably. | |
105 | If an error occurs the function returns a NULL pointer and fills in the | |
106 | error value pointed to by the <B>error</B> pointer supplied by the caller. | |
107 | </P> | |
108 | <P> | |
109 | The caller then passes the SRC_STATE object to the <B>src_callback_read</B> | |
110 | function to pull data out of the converter. | |
111 | When the caller is finished with the converter they should pass it to the | |
112 | clean up function <A HREF="api_full.html#CleanUp">src_delete</A>. | |
113 | </P> | |
114 | <P> | |
115 | The <B>func</B> parameter is a user supplied function which must match the | |
116 | <B>src_callback_t</B> type signature while <B>cb_data</B> is a pointer to | |
117 | data which be passed as the first parameter to the user supplied callback | |
118 | function. | |
119 | This function is called by the converter whenever it needs input data as a | |
120 | result of being calls to <B>src_callback_read</B>. | |
121 | </P> | |
122 | <P> | |
123 | If the converter was initialised to work with more than one channel, the | |
124 | callback function must work with mutiple channels of interleaved data. | |
125 | The callback function should return the number of frames it supplying to | |
126 | the converter. | |
127 | For multi channel files, this return value should be the number of floats | |
128 | divided by the number of channels. | |
129 | </P> | |
130 | <P> | |
131 | The converter must be one of the supplied converter types documented | |
132 | <A HREF="api_misc.html#Converters">here</A>. | |
133 | </P> | |
134 | <P> | |
135 | The caller then passes the SRC_STATE pointer to the <B>src_callback_read</B> | |
136 | function to pull data out of the converter. | |
137 | </P> | |
138 | ||
139 | <!-- pepper --> | |
140 | <A NAME="Read"></A> | |
141 | <H3><BR>Callback Read</H3> | |
142 | <PRE> | |
143 | long src_callback_read (SRC_STATE *state, double src_ratio, | |
144 | long frames, float *data) ; | |
145 | </PRE> | |
146 | <P> | |
147 | The <B>src_callback_read</B> function is passed the | |
148 | <A HREF="api_misc.html#SRC_DATA"><B>SRC_STATE</B></A> | |
149 | pointer returned by <B>src_callback_new</B>, the coversion ratio | |
150 | (output_sample_rate / input_sample_rate), the maximum number of output frames | |
151 | to generate and a pointer to a buffer in which to place the output data. | |
152 | For multi channel files, the data int the output buffer is stored in | |
153 | interleaved format. | |
154 | </P> | |
155 | <P> | |
156 | The <B>src_callback_read</B> function returns the number of frames generated | |
157 | or zero if an error occurs or it runs out of input (ie the user supplied | |
158 | callback function returns zero and there is no more data buffered internally). | |
159 | If an error has occurred, the function <A HREF="api_misc.html#ErrorReporting"> | |
160 | src_error</A> will return non-zero. | |
161 | </P> | |
162 | ||
163 | <P> | |
164 | See also : | |
165 | <A HREF="api_full.html#SetRatio"><B>src_set_ratio</B></A> | |
166 | </P> | |
167 | ||
168 | <!-- pepper --> | |
169 | ||
170 | </DIV> | |
171 | </TD></TR> | |
172 | </TABLE> | |
173 | ||
174 | </BODY> | |
175 | </HTML> | |
176 |