Separate bytes from programme time
An HTTP byte range identifies positions within a representation. A playback slider identifies positions on a media timeline. A player must relate those concepts using the container and media structure. A request for part of a large file is therefore a delivery operation, rather than a direct instruction such as play the next scene. Keep that distinction when interpreting requests generated after a seek.
Recognise the response context
Mozilla’s range-request guidance describes 206 Partial Content for a fulfilled range and 416 when a requested range cannot be satisfied. A server can also ignore a range request and return the full resource with 200. These statuses need the associated request and headers to be meaningful. A 206 response does not mean the whole movie was truncated accidentally, and a 200 is not automatically proof that seeking must fail.
Allow for the media’s decoding structure
The application can need index information and an appropriate decoding start point as well as the desired bytes. A cached interval, stream window and independent media file can behave differently. If playback starts normally but a specific seek fails, retain the destination position and observed outcome. Do not assume the account is invalid merely because the error appears only after jumping far into a programme.
Capture the smallest useful evidence
A publisher may need the requested range, response status, relevant headers and player error for an authorised reproduction. Redact private URLs and tokens before sharing them. Avoid editing Range headers or downloading repeated large intervals as an unexplained repair attempt. A clear record of the failing seek helps distinguish response handling, resource changes and media-index problems without treating every partial-content response as an error.
Questions, answered
Does HTTP 206 mean the server sent a broken video?
Not by itself. It can mean a requested part of the resource was supplied correctly. Interpret it with the Range request, response headers and actual playback result.