Standard MP4 files are recommended input source type, as opposed to standard MP4. In addition, the MP4 container is preferred over FLV.
Standard MP4 files have a single index of all keyframes that must be parsed before a stream can start. In most cases, FLV files do not have an index of keyframes, so seeking in the video is slower while the server searches to find the exact time to file offset mapping for each request.
Fragmented F4F files are also supported as a valid input source if the content is pre-encrypted using Adobe Access. Fragmented MP4 files have a nice balance because the index of keyframes is split and distributed throughout the fragments.