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Re: Media Fragment Question

From: Jack Jansen <Jack.Jansen@cwi.nl>
Date: Sun, 4 Jul 2010 22:08:06 +0200
Cc: Chris Double <chris.double@double.co.nz>, public-media-fragment@w3.org
Message-Id: <FBFB2ECA-4AF2-43CF-BBC5-14CE8AD091FF@cwi.nl>
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>

On 1 jul 2010, at 01:02, Silvia Pfeiffer wrote:

>> A user agent that does not support a particular media type (eg. a
>> browser that doesn't support .ogv) obviously can't play a file. But if
>> the page presents a link of the form:
>> 
>> <a href ='http://example.com/video.ogv#t=10,20>right click me and save</a>
>> 
>> Is it expected that the user agent, which supports media fragments,
>> would send the range requests to ensure only the correct time range is
>> saved even if the user agent itself can't play the file? If so, that
>> seems to indicate that the Range request needs to be sent on every
>> single request made by the user agent which doesn't sound like a good
>> idea.
> 
> Such a request won't result in a valid media resource and even if
> saved won't be playable. There are two things that a browser can do:
> * one is to ignore the fragment and download the full resource
> * second is to turn the fragment into a query, e.g.
> http://example.com/video.ogv?t=10,20 and hope that there is a server
> behind it that can interpret that query, encode the file on the server
> into a proper new resource and return it.
> 
> I am not sure if the second option is one that makes sense to browsers
> and as long as there aren't many servers that actually support the
> "transcoding", it won't be of much use anyway and return the full
> resource anyway. So, maybe you want to do the first option unless the
> resource is clearly in a audio or video element, or maybe it is
> directly addressed and you can try the header retrieval first to
> confirm it's a media resource and set up decoding.


First: Chris: thanks for the catch! This is an important one.

Second: whatever we decide is the best course of action for user agents: we should document it in our "guidelines" section (section 7?). If we didn't think of the right-click-save use case there's quite a good chance that implementors will also overlook it.

Third: I think our only reasonable option is to save the whole document. Trying to save the partial document is probably not going to work, as Silvia points out. Translating to query syntax is not guaranteed to work (and for file: URL would most likely not work, there not being any server to answer the query). Moreover, I'm pretty sure that saving the whole document is also what happens for right-click-save on fragment URLs for HTML or other documents.
--
Jack Jansen, <Jack.Jansen@cwi.nl>, http://www.cwi.nl/~jack
If I can't dance I don't want to be part of your revolution -- Emma Goldman
Received on Sunday, 4 July 2010 20:08:49 GMT

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