Downloading required components is normal. This happens because you have been uninstalling/reinstalling MC. When playing a video MC checks for needed components and download them if not present. In this case they were most likely LAV filters that were downloaded. This will happen only once (until you uninstall again).
Crashing may be related to something else. Next time it happens, restart MC and immediately grab the log files. Send the entire package as it may contain a crash dump file.