In terms of playback, the original format shouldn’t matter (although it may well impact what transcoding technology / settings you need) the important thing will be the target format. The older CatDV Web Client defaulted to using the QuickTime player in the browser, so could play back many QuickTime formatted files directly, but as support for plugins is removed from popular browsers, and is not typically available on mobile devices, so we have had to move with the times and migrate over to using the HTML5 video player component.
Using the HTML5 player component means that the supported proxy formats will depend entirely on what browser/device you are using. However, by far the most widely supported format is MP4 (H.264/AAC). This format should work on most browsers/devices, though sadly even this is not guaranteed to work in absolutely all platforms/browsers, as the H.264 codec is patent encumbered and therefore cannot be included in some strictly open source browsers.
Going forward expect to see support for multiple proxy formats, so that the correct format can be served out to different browsers/hosts – but that isn’t currently supported.