This heavily depends on the video encoder and container format.
Some are optimized for streaming and put their data information at the beginning of the file, however, there are other formats that put it at the end. Then you have to download it fully before being able to decode.
Starting in the middle is generally not how video decoders can work (they rely on information from frames before) and this arbitrary range will not work.
However, from experience, VLC was able to play almost anything I gave it. So if it fails, your splitting is not a supported approach.