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62 HREF="sdlbuildaudiocvt.html" |
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65 ></TD |
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66 ></TR |
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67 ></TABLE |
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68 ><HR |
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69 ALIGN="LEFT" |
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70 WIDTH="100%"></DIV |
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71 ><H1 |
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72 ><A |
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73 NAME="SDLAUDIOCVT" |
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74 ></A |
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75 >SDL_AudioCVT</H1 |
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76 ><DIV |
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77 CLASS="REFNAMEDIV" |
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78 ><A |
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79 NAME="AEN6884" |
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80 ></A |
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81 ><H2 |
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82 >Name</H2 |
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83 >SDL_AudioCVT -- Audio Conversion Structure</DIV |
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84 ><DIV |
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85 CLASS="REFSECT1" |
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86 ><A |
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87 NAME="AEN6887" |
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88 ></A |
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89 ><H2 |
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90 >Structure Definition</H2 |
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91 ><PRE |
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92 CLASS="PROGRAMLISTING" |
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93 >typedef struct{ |
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94 int needed; |
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95 Uint16 src_format; |
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96 Uint16 dest_format; |
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97 double rate_incr; |
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98 Uint8 *buf; |
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99 int len; |
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100 int len_cvt; |
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101 int len_mult; |
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102 double len_ratio; |
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103 void (*filters[10])(struct SDL_AudioCVT *cvt, Uint16 format); |
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104 int filter_index; |
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105 } SDL_AudioCVT;</PRE |
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106 ></DIV |
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107 ><DIV |
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108 CLASS="REFSECT1" |
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109 ><A |
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110 NAME="AEN6890" |
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111 ></A |
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112 ><H2 |
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113 >Structure Data</H2 |
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114 ><DIV |
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115 CLASS="INFORMALTABLE" |
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116 ><A |
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117 NAME="AEN6892" |
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118 ></A |
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119 ><P |
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120 ></P |
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121 ><TABLE |
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122 BORDER="0" |
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123 CLASS="CALSTABLE" |
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124 ><TBODY |
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125 ><TR |
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126 ><TD |
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127 ALIGN="LEFT" |
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128 VALIGN="TOP" |
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129 ><TT |
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130 CLASS="STRUCTFIELD" |
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131 ><I |
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132 >needed</I |
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133 ></TT |
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134 ></TD |
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135 ><TD |
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136 ALIGN="LEFT" |
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137 VALIGN="TOP" |
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138 >Set to one if the conversion is possible</TD |
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139 ></TR |
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140 ><TR |
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141 ><TD |
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142 ALIGN="LEFT" |
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143 VALIGN="TOP" |
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144 ><TT |
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145 CLASS="STRUCTFIELD" |
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146 ><I |
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147 >src_format</I |
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148 ></TT |
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149 ></TD |
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150 ><TD |
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151 ALIGN="LEFT" |
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152 VALIGN="TOP" |
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153 >Audio format of the source</TD |
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154 ></TR |
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155 ><TR |
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156 ><TD |
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157 ALIGN="LEFT" |
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158 VALIGN="TOP" |
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159 ><TT |
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160 CLASS="STRUCTFIELD" |
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161 ><I |
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162 >dest_format</I |
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163 ></TT |
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164 ></TD |
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165 ><TD |
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166 ALIGN="LEFT" |
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167 VALIGN="TOP" |
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168 >Audio format of the destination</TD |
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169 ></TR |
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170 ><TR |
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171 ><TD |
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172 ALIGN="LEFT" |
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173 VALIGN="TOP" |
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174 ><TT |
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175 CLASS="STRUCTFIELD" |
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176 ><I |
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177 >rate_incr</I |
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178 ></TT |
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179 ></TD |
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180 ><TD |
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181 ALIGN="LEFT" |
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182 VALIGN="TOP" |
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183 >Rate conversion increment</TD |
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184 ></TR |
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185 ><TR |
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186 ><TD |
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187 ALIGN="LEFT" |
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188 VALIGN="TOP" |
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189 ><TT |
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190 CLASS="STRUCTFIELD" |
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191 ><I |
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192 >buf</I |
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193 ></TT |
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194 ></TD |
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195 ><TD |
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196 ALIGN="LEFT" |
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197 VALIGN="TOP" |
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198 >Audio buffer</TD |
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199 ></TR |
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200 ><TR |
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201 ><TD |
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202 ALIGN="LEFT" |
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203 VALIGN="TOP" |
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204 ><TT |
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205 CLASS="STRUCTFIELD" |
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206 ><I |
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207 >len</I |
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208 ></TT |
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209 ></TD |
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210 ><TD |
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211 ALIGN="LEFT" |
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212 VALIGN="TOP" |
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213 >Length of the original audio buffer in bytes</TD |
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214 ></TR |
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215 ><TR |
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216 ><TD |
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217 ALIGN="LEFT" |
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218 VALIGN="TOP" |
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219 ><TT |
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220 CLASS="STRUCTFIELD" |
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221 ><I |
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222 >len_cvt</I |
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223 ></TT |
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224 ></TD |
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225 ><TD |
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226 ALIGN="LEFT" |
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227 VALIGN="TOP" |
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228 >Length of converted audio buffer in bytes (calculated)</TD |
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229 ></TR |
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230 ><TR |
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231 ><TD |
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232 ALIGN="LEFT" |
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233 VALIGN="TOP" |
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234 ><TT |
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235 CLASS="STRUCTFIELD" |
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236 ><I |
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237 >len_mult</I |
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238 ></TT |
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239 ></TD |
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240 ><TD |
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241 ALIGN="LEFT" |
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242 VALIGN="TOP" |
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243 ><TT |
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244 CLASS="STRUCTFIELD" |
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245 ><I |
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246 >buf</I |
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247 ></TT |
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248 > must be <TT |
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249 CLASS="STRUCTFIELD" |
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250 ><I |
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251 >len</I |
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252 ></TT |
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253 >*<TT |
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254 CLASS="STRUCTFIELD" |
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255 ><I |
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256 >len_mult</I |
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257 ></TT |
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258 > bytes in size(calculated)</TD |
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259 ></TR |
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260 ><TR |
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261 ><TD |
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262 ALIGN="LEFT" |
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263 VALIGN="TOP" |
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264 ><TT |
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265 CLASS="STRUCTFIELD" |
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266 ><I |
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267 >len_ratio</I |
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268 ></TT |
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269 ></TD |
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270 ><TD |
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271 ALIGN="LEFT" |
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272 VALIGN="TOP" |
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273 >Final audio size is <TT |
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274 CLASS="STRUCTFIELD" |
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275 ><I |
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276 >len</I |
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277 ></TT |
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278 >*<TT |
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279 CLASS="STRUCTFIELD" |
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280 ><I |
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281 >len_ratio</I |
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282 ></TT |
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283 ></TD |
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284 ></TR |
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285 ><TR |
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286 ><TD |
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287 ALIGN="LEFT" |
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288 VALIGN="TOP" |
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289 ><TT |
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290 CLASS="STRUCTFIELD" |
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291 ><I |
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292 >filters[10](..)</I |
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293 ></TT |
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294 ></TD |
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295 ><TD |
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296 ALIGN="LEFT" |
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297 VALIGN="TOP" |
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298 >Pointers to functions needed for this conversion</TD |
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299 ></TR |
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300 ><TR |
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301 ><TD |
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302 ALIGN="LEFT" |
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303 VALIGN="TOP" |
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304 ><TT |
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305 CLASS="STRUCTFIELD" |
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306 ><I |
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307 >filter_index</I |
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308 ></TT |
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309 ></TD |
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310 ><TD |
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311 ALIGN="LEFT" |
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312 VALIGN="TOP" |
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313 >Current conversion function</TD |
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314 ></TR |
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315 ></TBODY |
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316 ></TABLE |
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317 ><P |
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318 ></P |
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319 ></DIV |
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320 ></DIV |
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321 ><DIV |
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322 CLASS="REFSECT1" |
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323 ><A |
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324 NAME="AEN6944" |
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325 ></A |
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326 ><H2 |
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327 >Description</H2 |
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328 ><P |
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329 >The <SPAN |
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330 CLASS="STRUCTNAME" |
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331 >SDL_AudioCVT</SPAN |
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332 > is used to convert audio data between different formats. A <SPAN |
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333 CLASS="STRUCTNAME" |
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334 >SDL_AudioCVT</SPAN |
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335 > structure is created with the <A |
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336 HREF="sdlbuildaudiocvt.html" |
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337 ><TT |
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338 CLASS="FUNCTION" |
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339 >SDL_BuildAudioCVT</TT |
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340 ></A |
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341 > function, while the actual conversion is done by the <A |
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342 HREF="sdlconvertaudio.html" |
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343 ><TT |
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344 CLASS="FUNCTION" |
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345 >SDL_ConvertAudio</TT |
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346 ></A |
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347 > function.</P |
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348 ><P |
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349 >Many of the fields in the <SPAN |
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350 CLASS="STRUCTNAME" |
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351 >SDL_AudioCVT</SPAN |
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352 > structure should be considered private and their function will not be discussed here.</P |
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353 ><P |
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354 ></P |
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355 ><DIV |
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356 CLASS="VARIABLELIST" |
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357 ><DL |
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358 ><DT |
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359 ><SPAN |
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360 CLASS="TYPE" |
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361 >Uint8 *</SPAN |
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362 ><TT |
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363 CLASS="STRUCTFIELD" |
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364 ><I |
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365 >buf</I |
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366 ></TT |
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367 ></DT |
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368 ><DD |
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369 ><P |
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370 >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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371 CLASS="STRUCTFIELD" |
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372 ><I |
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373 >buf</I |
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374 ></TT |
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375 > is large enough. See below.</P |
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376 ></DD |
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377 ><DT |
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378 ><SPAN |
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379 CLASS="TYPE" |
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380 >int</SPAN |
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381 > <TT |
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382 CLASS="STRUCTFIELD" |
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383 ><I |
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384 >len</I |
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385 ></TT |
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386 ></DT |
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387 ><DD |
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388 ><P |
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389 >This is the length of the original audio data in bytes.</P |
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390 ></DD |
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391 ><DT |
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392 ><SPAN |
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393 CLASS="TYPE" |
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394 >int</SPAN |
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395 > <TT |
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396 CLASS="STRUCTFIELD" |
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397 ><I |
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398 >len_mult</I |
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399 ></TT |
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400 ></DT |
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401 ><DD |
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402 ><P |
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403 >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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404 CLASS="STRUCTFIELD" |
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405 ><I |
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406 >buf</I |
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407 ></TT |
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408 > should be <TT |
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409 CLASS="STRUCTFIELD" |
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410 ><I |
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411 >len</I |
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412 ></TT |
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413 >*<TT |
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414 CLASS="STRUCTFIELD" |
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415 ><I |
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416 >len_mult</I |
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417 ></TT |
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418 >.</P |
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419 ></DD |
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420 ><DT |
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421 ><SPAN |
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422 CLASS="TYPE" |
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423 >double</SPAN |
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424 > <TT |
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425 CLASS="STRUCTFIELD" |
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426 ><I |
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427 >len_ratio</I |
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428 ></TT |
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429 ></DT |
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430 ><DD |
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431 ><P |
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432 >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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433 CLASS="STRUCTFIELD" |
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434 ><I |
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435 >len</I |
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436 ></TT |
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437 >*<TT |
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438 CLASS="STRUCTFIELD" |
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439 ><I |
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440 >len_ratio</I |
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441 ></TT |
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442 > is the size of the converted audio data in bytes. This is very similar to <TT |
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443 CLASS="STRUCTFIELD" |
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444 ><I |
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445 >len_mult</I |
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446 ></TT |
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447 >, however when the convert audio data is shorter than the original <TT |
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448 CLASS="STRUCTFIELD" |
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449 ><I |
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450 >len_mult</I |
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451 ></TT |
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452 > would be 1. <TT |
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453 CLASS="STRUCTFIELD" |
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454 ><I |
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455 >len_ratio</I |
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456 ></TT |
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457 >, on the other hand, would be a fractional number between 0 and 1.</P |
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458 ></DD |
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459 ></DL |
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460 ></DIV |
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461 ></DIV |
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462 ><DIV |
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463 CLASS="REFSECT1" |
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464 ><A |
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465 NAME="AEN6989" |
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466 ></A |
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467 ><H2 |
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468 >See Also</H2 |
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469 ><P |
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470 ><A |
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471 HREF="sdlbuildaudiocvt.html" |
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472 ><TT |
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473 CLASS="FUNCTION" |
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474 >SDL_BuildAudioCVT</TT |
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475 ></A |
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476 >, |
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477 <A |
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478 HREF="sdlconvertaudio.html" |
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479 ><TT |
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480 CLASS="FUNCTION" |
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481 >SDL_ConvertAudio</TT |
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482 ></A |
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483 >, |
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484 <A |
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485 HREF="sdlaudiospec.html" |
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486 ><SPAN |
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487 CLASS="STRUCTNAME" |
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488 >SDL_AudioSpec</SPAN |
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489 ></A |
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490 ></P |
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