"Accept-Ranges" is not required.

[heroboy]

https://github.com/kiewic/MediaElementWithHttpClient/blob/master/MediaElementWithHttpClient/HttpRandomAccessStream.cs#L75

from:https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.5

but are not required to do so. Clients MAY generate byte-range
requests without having received this header for the resource
involved.

[kiewic]

@heroboy That is a good point.

Thanks for letting me know.