It is possible that your video file format is supported by SlideShare, but it may still not convert (giving an error) after uploading. This is because video formats consist of a container and inside this container, the audio and video codecs reside. For the file to convert, the codecs have to be supported by SlideShare.

That is how video formats work and yes, we agree it is somewhat confusing. To understand this better, please read this link.  The list of containers supported by SlideShare is here, and the list of audio and video codecs we support is here.

The above lists should cover most formats that you are likely to use on your computer, mobile, cameras or other electronic devices. If you are still using a different format and need to upload to SlideShare, converting your video to MPEG4 video with MP3 audio is a safe bet.