Why does Firebug show a "206 Partial Content" response on a video loading request?
I have a bunch of html5 video elements, with their preload attribute set to "auto". They start loading just fine, but I think there might be a problem with their caching, because each time I reload the page (without clearing the cache), they start all over again.
When I checked the Network panel in firebug, I noticed everything else (images and files) was giving me a "304 not modified" message as espected, while the videos (and audio) files were giving me a "206 partial content" message, in duplicated entries.
The "206 partial content" response also appears in duplicated entries when the page is loaded with the cache cleared, instead of a "200 OK" response, as it would be expected.
Is this a normal behavior for video and audio elements? If not, how could it be corrected?
Answer
This Partial Content code (206) may be sent from the server when the client has asked for a range (e.g. "give me the first 2MB of video data").
It is vital for downloading data in chunks which avoids fetching unused resources. (I seldom watch a full video online.) Look at the outgoing request for a Range header.
See Status Codes (RFC2616 - HTTP/1.1) (note that any 2xx code means "Success"):
10.2.7 206 Partial Content:
The server has fulfilled the partial GET request for the resource. The request MUST have included a Range header field (section 14.35) indicating the desired range, and MAY have included an If-Range header field (section 14.27) to make the request conditional.
And from the Range header section:
If the server supports the Range header and the specified range or ranges are appropriate for the entity
- The presence of a Range header in an unconditional GET modifies what is returned if the GET is otherwise successful. In other words, the response carries a status code of 206 (Partial Content) instead of 200 (OK).
I do not understand the intricicies of caching and/or ETags or what to expect in FireFox, however.