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1 <HTML
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2 ><HEAD
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3 ><TITLE
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4 >SDL_AudioCVT</TITLE
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5 ><META
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6 NAME="GENERATOR"
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7 CONTENT="Modular DocBook HTML Stylesheet Version 1.61
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8 "><LINK
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9 REL="HOME"
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10 TITLE="SDL Library Documentation"
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11 HREF="index.html"><LINK
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12 REL="UP"
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13 TITLE="Audio"
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14 HREF="audio.html"><LINK
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15 REL="PREVIOUS"
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16 TITLE="SDL_FreeWAV"
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17 HREF="sdlfreewav.html"><LINK
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18 REL="NEXT"
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19 TITLE="SDL_BuildAudioCVT"
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20 HREF="sdlbuildaudiocvt.html"></HEAD
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21 ><BODY
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22 CLASS="REFENTRY"
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26 VLINK="#551a8b"
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27 ALINK="#ff0000"
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28 ><DIV
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29 CLASS="NAVHEADER"
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30 ><TABLE
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31 WIDTH="100%"
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32 BORDER="0"
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33 CELLPADDING="0"
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34 CELLSPACING="0"
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35 ><TR
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36 ><TH
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37 COLSPAN="3"
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38 ALIGN="center"
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39 >SDL Library Documentation</TH
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40 ></TR
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41 ><TR
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42 ><TD
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43 WIDTH="10%"
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44 ALIGN="left"
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45 VALIGN="bottom"
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46 ><A
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47 HREF="sdlfreewav.html"
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48 >Prev</A
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49 ></TD
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50 ><TD
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51 WIDTH="80%"
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52 ALIGN="center"
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53 VALIGN="bottom"
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54 ></TD
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55 ><TD
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56 WIDTH="10%"
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57 ALIGN="right"
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58 VALIGN="bottom"
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59 ><A
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60 HREF="sdlbuildaudiocvt.html"
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61 >Next</A
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62 ></TD
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63 ></TR
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64 ></TABLE
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65 ><HR
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66 ALIGN="LEFT"
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67 WIDTH="100%"></DIV
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68 ><H1
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69 ><A
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70 NAME="SDLAUDIOCVT"
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71 >SDL_AudioCVT</A
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72 ></H1
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73 ><DIV
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74 CLASS="REFNAMEDIV"
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75 ><A
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76 NAME="AEN6262"
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77 ></A
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78 ><H2
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79 >Name</H2
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80 >SDL_AudioCVT -- Audio Conversion Structure</DIV
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81 ><DIV
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82 CLASS="REFSECT1"
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83 ><A
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84 NAME="AEN6265"
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85 ></A
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86 ><H2
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87 >Structure Definition</H2
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88 ><PRE
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89 CLASS="PROGRAMLISTING"
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90 >typedef struct{
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91 int needed;
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92 Uint16 src_format;
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93 Uint16 dest_format;
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94 double rate_incr;
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95 Uint8 *buf;
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96 int len;
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97 int len_cvt;
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98 int len_mult;
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99 double len_ratio;
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100 void (*filters[10])(struct SDL_AudioCVT *cvt, Uint16 format);
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101 int filter_index;
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102 } SDL_AudioCVT;</PRE
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103 ></DIV
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104 ><DIV
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105 CLASS="REFSECT1"
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106 ><A
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107 NAME="AEN6268"
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108 ></A
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109 ><H2
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110 >Structure Data</H2
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111 ><DIV
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112 CLASS="INFORMALTABLE"
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113 ><A
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114 NAME="AEN6270"
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115 ></A
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116 ><P
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117 ></P
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118 ><TABLE
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119 BORDER="0"
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120 CLASS="CALSTABLE"
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121 ><TBODY
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122 ><TR
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123 ><TD
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124 ALIGN="LEFT"
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125 VALIGN="TOP"
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126 ><TT
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127 CLASS="STRUCTFIELD"
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128 ><I
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129 >needed</I
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130 ></TT
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131 ></TD
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132 ><TD
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133 ALIGN="LEFT"
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134 VALIGN="TOP"
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135 >Set to one if the conversion is possible</TD
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136 ></TR
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137 ><TR
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138 ><TD
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139 ALIGN="LEFT"
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140 VALIGN="TOP"
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141 ><TT
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142 CLASS="STRUCTFIELD"
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143 ><I
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144 >src_format</I
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145 ></TT
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146 ></TD
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147 ><TD
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148 ALIGN="LEFT"
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149 VALIGN="TOP"
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150 >Audio format of the source</TD
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151 ></TR
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152 ><TR
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153 ><TD
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154 ALIGN="LEFT"
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155 VALIGN="TOP"
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156 ><TT
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157 CLASS="STRUCTFIELD"
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158 ><I
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159 >dest_format</I
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160 ></TT
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161 ></TD
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162 ><TD
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163 ALIGN="LEFT"
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164 VALIGN="TOP"
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165 >Audio format of the destination</TD
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166 ></TR
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167 ><TR
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168 ><TD
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169 ALIGN="LEFT"
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170 VALIGN="TOP"
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171 ><TT
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172 CLASS="STRUCTFIELD"
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173 ><I
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174 >rate_incr</I
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175 ></TT
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176 ></TD
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177 ><TD
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178 ALIGN="LEFT"
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179 VALIGN="TOP"
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180 >Rate conversion increment</TD
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181 ></TR
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182 ><TR
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183 ><TD
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184 ALIGN="LEFT"
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185 VALIGN="TOP"
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186 ><TT
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187 CLASS="STRUCTFIELD"
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188 ><I
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189 >buf</I
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190 ></TT
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191 ></TD
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192 ><TD
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193 ALIGN="LEFT"
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194 VALIGN="TOP"
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195 >Audio buffer</TD
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196 ></TR
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197 ><TR
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198 ><TD
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199 ALIGN="LEFT"
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200 VALIGN="TOP"
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201 ><TT
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202 CLASS="STRUCTFIELD"
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203 ><I
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204 >len</I
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205 ></TT
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206 ></TD
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207 ><TD
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208 ALIGN="LEFT"
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209 VALIGN="TOP"
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210 >Length of the original audio buffer in bytes</TD
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211 ></TR
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212 ><TR
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213 ><TD
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214 ALIGN="LEFT"
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215 VALIGN="TOP"
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216 ><TT
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217 CLASS="STRUCTFIELD"
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218 ><I
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219 >len_cvt</I
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220 ></TT
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221 ></TD
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222 ><TD
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223 ALIGN="LEFT"
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224 VALIGN="TOP"
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225 >Length of converted audio buffer in bytes (calculated)</TD
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226 ></TR
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227 ><TR
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228 ><TD
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229 ALIGN="LEFT"
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230 VALIGN="TOP"
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231 ><TT
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232 CLASS="STRUCTFIELD"
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233 ><I
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234 >len_mult</I
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235 ></TT
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236 ></TD
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237 ><TD
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238 ALIGN="LEFT"
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239 VALIGN="TOP"
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240 ><TT
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241 CLASS="STRUCTFIELD"
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242 ><I
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243 >buf</I
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244 ></TT
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245 > must be <TT
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246 CLASS="STRUCTFIELD"
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247 ><I
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248 >len</I
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249 ></TT
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250 >*<TT
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251 CLASS="STRUCTFIELD"
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252 ><I
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253 >len_mult</I
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254 ></TT
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255 > bytes in size(calculated)</TD
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256 ></TR
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257 ><TR
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258 ><TD
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259 ALIGN="LEFT"
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260 VALIGN="TOP"
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261 ><TT
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262 CLASS="STRUCTFIELD"
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263 ><I
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264 >len_ratio</I
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265 ></TT
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266 ></TD
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267 ><TD
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268 ALIGN="LEFT"
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269 VALIGN="TOP"
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270 >Final audio size is <TT
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271 CLASS="STRUCTFIELD"
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272 ><I
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273 >len</I
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274 ></TT
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275 >*<TT
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276 CLASS="STRUCTFIELD"
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277 ><I
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278 >len_ratio</I
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279 ></TT
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280 ></TD
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281 ></TR
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282 ><TR
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283 ><TD
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284 ALIGN="LEFT"
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285 VALIGN="TOP"
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286 ><TT
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287 CLASS="STRUCTFIELD"
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288 ><I
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289 >filters[10](..)</I
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290 ></TT
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291 ></TD
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292 ><TD
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293 ALIGN="LEFT"
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294 VALIGN="TOP"
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295 >Pointers to functions needed for this conversion</TD
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296 ></TR
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297 ><TR
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298 ><TD
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299 ALIGN="LEFT"
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300 VALIGN="TOP"
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301 ><TT
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302 CLASS="STRUCTFIELD"
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303 ><I
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304 >filter_index</I
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305 ></TT
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306 ></TD
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307 ><TD
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308 ALIGN="LEFT"
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309 VALIGN="TOP"
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310 >Current conversion function</TD
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311 ></TR
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312 ></TBODY
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313 ></TABLE
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314 ><P
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315 ></P
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316 ></DIV
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317 ></DIV
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318 ><DIV
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319 CLASS="REFSECT1"
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320 ><A
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321 NAME="AEN6322"
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322 ></A
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323 ><H2
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324 >Description</H2
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325 ><P
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326 >The <SPAN
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327 CLASS="STRUCTNAME"
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328 >SDL_AudioCVT</SPAN
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329 > is used to convert audio data between different formats. A <SPAN
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330 CLASS="STRUCTNAME"
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331 >SDL_AudioCVT</SPAN
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332 > structure is created with the <A
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333 HREF="sdlbuildaudiocvt.html"
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334 ><TT
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335 CLASS="FUNCTION"
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336 >SDL_BuildAudioCVT</TT
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337 ></A
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338 > function, while the actual conversion is done by the <A
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339 HREF="sdlconvertaudio.html"
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340 ><TT
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341 CLASS="FUNCTION"
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342 >SDL_ConvertAudio</TT
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343 ></A
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344 > function.</P
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345 ><P
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346 >Many of the fields in the <SPAN
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347 CLASS="STRUCTNAME"
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348 >SDL_AudioCVT</SPAN
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349 > structure should be considered private and their function will not be discussed here.</P
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350 ><P
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351 ></P
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352 ><DIV
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353 CLASS="VARIABLELIST"
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354 ><DL
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355 ><DT
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356 ><SPAN
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357 CLASS="TYPE"
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358 >Uint8 *</SPAN
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359 ><TT
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360 CLASS="STRUCTFIELD"
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361 ><I
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362 >buf</I
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363 ></TT
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364 ></DT
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365 ><DD
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366 ><P
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367 >This points to the audio data that will be used in the conversion. It is both the source and the destination, which means the converted audio data overwrites the original data. It also means that the converted data may be larger than the original data (if you were converting from 8-bit to 16-bit, for instance), so you must ensure <TT
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368 CLASS="STRUCTFIELD"
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369 ><I
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370 >buf</I
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371 ></TT
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372 > is large enough. See below.</P
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373 ></DD
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374 ><DT
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375 ><SPAN
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376 CLASS="TYPE"
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377 >int</SPAN
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378 > <TT
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379 CLASS="STRUCTFIELD"
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380 ><I
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381 >len</I
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382 ></TT
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383 ></DT
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384 ><DD
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385 ><P
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386 >This is the length of the original audio data in bytes.</P
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387 ></DD
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388 ><DT
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389 ><SPAN
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390 CLASS="TYPE"
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391 >int</SPAN
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392 > <TT
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393 CLASS="STRUCTFIELD"
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394 ><I
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395 >len_mult</I
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396 ></TT
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397 ></DT
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398 ><DD
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399 ><P
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400 >As explained above, the audio buffer needs to be big enough to store the converted data, which may be bigger than the original audio data. The length of <TT
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401 CLASS="STRUCTFIELD"
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402 ><I
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403 >buf</I
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404 ></TT
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405 > should be <TT
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406 CLASS="STRUCTFIELD"
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407 ><I
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408 >len</I
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409 ></TT
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410 >*<TT
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411 CLASS="STRUCTFIELD"
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412 ><I
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413 >len_mult</I
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414 ></TT
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415 >.</P
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416 ></DD
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417 ><DT
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418 ><SPAN
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419 CLASS="TYPE"
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420 >double</SPAN
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421 > <TT
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422 CLASS="STRUCTFIELD"
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423 ><I
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424 >len_ratio</I
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425 ></TT
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426 ></DT
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427 ><DD
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428 ><P
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429 >When you have finished converting your audio data, you need to know how much of your audio buffer is valid. <TT
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430 CLASS="STRUCTFIELD"
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431 ><I
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432 >len</I
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433 ></TT
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434 >*<TT
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435 CLASS="STRUCTFIELD"
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436 ><I
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437 >len_ratio</I
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438 ></TT
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439 > is the size of the converted audio data in bytes. This is very similar to <TT
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440 CLASS="STRUCTFIELD"
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441 ><I
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442 >len_mult</I
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443 ></TT
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444 >, however when the convert audio data is shorter than the original <TT
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445 CLASS="STRUCTFIELD"
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446 ><I
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447 >len_mult</I
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448 ></TT
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449 > would be 1. <TT
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450 CLASS="STRUCTFIELD"
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451 ><I
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452 >len_ratio</I
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453 ></TT
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454 >, on the other hand, would be a fractional number between 0 and 1.</P
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455 ></DD
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456 ></DL
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457 ></DIV
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458 ></DIV
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459 ><DIV
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460 CLASS="REFSECT1"
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461 ><A
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462 NAME="AEN6367"
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463 ></A
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464 ><H2
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465 >See Also</H2
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466 ><P
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467 ><A
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468 HREF="sdlbuildaudiocvt.html"
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469 ><TT
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470 CLASS="FUNCTION"
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471 >SDL_BuildAudioCVT</TT
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472 ></A
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473 >,
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474 <A
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475 HREF="sdlconvertaudio.html"
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476 ><TT
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477 CLASS="FUNCTION"
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478 >SDL_ConvertAudio</TT
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479 ></A
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480 >,
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481 <A
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482 HREF="sdlaudiospec.html"
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483 ><SPAN
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484 CLASS="STRUCTNAME"
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485 >SDL_AudioSpec</SPAN
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486 ></A
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487 ></P
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488 ></DIV
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489 ><DIV
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490 CLASS="NAVFOOTER"
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491 ><HR
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492 ALIGN="LEFT"
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493 WIDTH="100%"><TABLE
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494 WIDTH="100%"
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495 BORDER="0"
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496 CELLPADDING="0"
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497 CELLSPACING="0"
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498 ><TR
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499 ><TD
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500 WIDTH="33%"
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501 ALIGN="left"
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502 VALIGN="top"
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503 ><A
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504 HREF="sdlfreewav.html"
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505 >Prev</A
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506 ></TD
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507 ><TD
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508 WIDTH="34%"
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509 ALIGN="center"
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510 VALIGN="top"
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511 ><A
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512 HREF="index.html"
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513 >Home</A
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514 ></TD
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515 ><TD
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516 WIDTH="33%"
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517 ALIGN="right"
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518 VALIGN="top"
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519 ><A
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520 HREF="sdlbuildaudiocvt.html"
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521 >Next</A
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522 ></TD
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523 ></TR
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524 ><TR
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525 ><TD
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526 WIDTH="33%"
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527 ALIGN="left"
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528 VALIGN="top"
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529 >SDL_FreeWAV</TD
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530 ><TD
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531 WIDTH="34%"
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532 ALIGN="center"
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533 VALIGN="top"
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534 ><A
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535 HREF="audio.html"
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536 >Up</A
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537 ></TD
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538 ><TD
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539 WIDTH="33%"
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540 ALIGN="right"
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541 VALIGN="top"
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542 >SDL_BuildAudioCVT</TD
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543 ></TR
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544 ></TABLE
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545 ></DIV
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546 ></BODY
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547 ></HTML
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548 > |
