Returns if sounds played from this source will support seeking via ISound::setPlayPosition(). If a sound is seekable depends on the file type and the audio format. For example MOD files cannot be seeked currently. Returns true of the sound source supports setPlayPosition() and false if not. Note: If the sound never has been played before, the sound engine will have to open the file and try to get the information from there, so this call could take a bit depending on the type of file.