PreferredFormatFor
status_t PreferredFormatFor(int fmt, media_format &format, bool rec=false);
status_t err = engine->PreferredFormatFor(channel->fOSSFormatFlags, *format, true);
status_t err = engine->PreferredFormatFor(fmt, mediaInput.format);
status_t err = engine->PreferredFormatFor(fmt, preferredFormat);