[whatwg] Video with MIME type application/octet-stream

Roger Hågensen rescator at emsai.net
Mon Sep 13 06:44:35 PDT 2010

  On 2010-09-13 15:03, Mikko Rantalainen wrote:
> 2010-09-11 01:51 EEST: Roger Hågensen:
>>   On 2010-09-09 09:24, Philip Jägenstedt wrote:
>>> For at least WAVE, Ogg and WebM it's not possible as they begin with
>>> different magic bytes.
>> Then why not define a new "magic" that is universal, so that if a proper
>> content type is not stated then a sniffing for a standardized universal
>> magic is done?
>> Yep, I'm referring to my BINID proposal.
>> If a content type is missing, sniff the first 265 bytes and see if it is
>> a BINID, if it is a BINID check if it's a supported/expected one, and it
>> is then play away, all is good.
>  From the "what could possibly go wrong" department of thought:
> - a web server blindly prefixes files with BINID if it "knows" the file
> suffix and as a result, a file ends up with a double BINID (server
> assumes that no files contain BINID by default)
> - a file has double BINID with contradicting content ids
> - some internal API assumes that caller wants BINID in the stream, the
> caller assumes that the stream has no BINID - as a result, the caller
> will pass content with BINIDs embedded in the middle of stream.
> Basically, this sounds like all the issues of BOM for all binary files.
> And why do we need this? Because web servers are not behaving correctly
> and are sending incorrect Content-Type headers? What makes you believe
> that BINID will not be incorrectly used?

Because if they add a binary id then they obviously are aware of the 
Old servers/software would just pass the file through as they are 
unaware so content type issues still exist there,
eventually old servers/software are rotate out until most are binary id 
This is how rolling out new standards work.
A server would only add a binary id if none exist and it's certain (by 
previous sniffing) that it's guess is correct,
though I guess the standard could state that if no binary id exist on a 
file then none should be added by the server at all (legacy behavior?)
And what I meant with the server adding it I meant services like Youtube 
(if Youtube transcode a video to MP4 then the server knows it's 
delivering just that),
likewise with streaming radio or video or similar, a regular webserver 
would have no right (or point) in modifying a file served than it does a 
.zip or .mp3 that a user downloads,
we are talking about streaming here mainly right? (where a short max 
length sniffing would be a huge benefit)

> (If you really believe that you can force content authors to provide
> correct BINIDs, why you cannot force content authors to provide correct
> Content-Types? Hopefully the goal is not to sniff if BINIDs seems okay
> and ignore "clearly incorrect" ones in the future...)

I do not see why web authors (or users at all) would need to mess with 
the binary id at all,
it's authoring software or transcoding software that would add them.

My BINID proposal is just that, a proposal for a binary id, it does not 
define how servers and browsers should handle it
as that is a different scope altogether. Something like a binary id 
would need a proper RFC writeup or similar.

> I'd like to specify that the only cases an UA is allowed to sniff the
> content type are:
> - Content-Type header is missing (because the server clearly does not
> know the type), or
> - Content-Type is literal "text/plain", "text/plain;
> charset=iso-8859-1", "text/plain; charset=ISO-8859-1" or "text/plain;
> charset=UTF-8" (to deal with historical mess caused by IIS and Apache), or
> - Content-Type is literal "application/octet-stream"
> (In all these cases, the server clearly has no real knowledge. If a file
> is meant for downloading, the server should use Content-Disposition:
> attachment header instead of hacks such as using
> "application/x-download" for Content-Type.)
Yes! But if the UA in those cases also checked for a binary ID (and 
found such) there would hardly be any ambiguity.
> For any other value of Content-Type, honor the type specified in HTTP
> level. And provide no overrides of any kind on any level above the HTTP.
> Levels above HTTP may provide HINTS about the content that can be used
> to aid or override *sniffing* but nothing should override any
> *explicitly specified Content-Type*. [This is simplified version of the
> logic that the Mozilla/Firefox already applies:
> http://mxr.mozilla.org/mozilla-central/source/netwerk/streamconv/converters/nsUnknownDecoder.cpp#684]
> And for heavens sake, do not specify any sniffing as "official".
> Instead, explicitly specify all sniffing as UA specific and possibly
> suggest that UAs should inform the user that content is broken and the
> current rendering is best effort if any sniffing is required.

Any sniffing would be as a fallback only if the UA suspects the content 
type is wrong (i.e. <video> of type text for example) or similar,
and it would not hurt to have some standardized behavior in those cases 
that sniff for something simple like a short binary id rather than parse 
potentially several kilobytes of the stream (which was where this 
discussion took off originally).

Roger "Rescator" Hågensen.
Freelancer - http://EmSai.net/

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