Write the expected count before the request
HTTP byte offsets start at zero and include both endpoints under RFC 9110. For an invented request covering offsets 1200 through 2199, the expected count is 1000 bytes: last minus first plus one. Subtracting endpoints without the final one creates an off-by-one error in a validator.
Keep three columns in the review record: requested start, requested end and expected byte count. A range length is not the same thing as its final offset. This matters when a packager records an offset-plus-length pair but the HTTP request uses start-and-end notation.
Check the actual response
For a successful single-range response, compare status, Content-Range and the actual payload length. Retain the full representation length reported where available. A plausible response header alone cannot establish that the expected bytes were transferred.
Use a stable owned resource and keep its generation identity in the report. If the representation changes during the check, the arithmetic may be correct while the comparison combines different files. Avoid debugging a moving target by repeatedly overwriting the same test object.
Keep format validation separate
Correct range delivery only answers a transport question. It does not prove the selected bytes form an independently decodable media unit, contain the required initialisation, or align with a container boundary. Review the packaging references as a separate step.
When sharing evidence, a short record of method, range, response and resource generation is more useful than a bare statement that seeking failed. Remove private URL parameters before circulation. This is a proposed origin check; no request has been sent to an IPTV Europe media resource.
Questions answered
How many bytes are offsets 1200 through 2199?
There are 1000 bytes because both endpoints are included.
Does a correct byte count prove the range is playable video?
No. Media boundaries and decoding context require their own checks.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.