Create an audio sample format converter context
@param out_fmt Output sample format
@param in_fmt Input sample format
@param channels Number of channels
@param flags See AV_CPU_FLAG_xx
@param ch_map list of the channels id to pick from the source stream, NULL
if all channels must be selected
@return NULL on error
Create an audio sample format converter context @param out_fmt Output sample format @param in_fmt Input sample format @param channels Number of channels @param flags See AV_CPU_FLAG_xx @param ch_map list of the channels id to pick from the source stream, NULL if all channels must be selected @return NULL on error