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[whatwg] Improving <video preload>?

From: Mikko Rantalainen <mikko.rantalainen@peda.net>
Date: Fri, 27 Mar 2015 12:43:37 +0200
Message-ID: <55153459.7090900@peda.net>
To: whatwg <whatwg@lists.whatwg.org>
The <video> element currently supports only 3 possible values for 
@preload attribute [1]. Real world user agent implementations agree on 
keyword "none" only. Both "metadata" and "auto" have a pretty poor 
interoperability, especially considering the amount of actual data 
transferred if user never hits "play" [2].

For example, current Chrome defaults to loading first 25 seconds of 
video even with value "metadata". If one has high quality HD video as 
the source, 25 seconds may be around 20 MB which is pretty much above 
the size I would expect to contain only "metadata".

Would it be possible to allow data sizes in @preload attribute in 
addition to keywords?

For example, <video preload="100KB"> would preload the first 100 KB of 
video file if user never hits the "play". Granted, this puts some 
additional burden on content authoring but it would allow having some 
preloading instead of currently available "none" for many services. Both 
"auto" and "metadata" load way too much to be usable in many user agents.

While streaming, the preload amount should be assumed to mean additional 
buffering over the automatic buffering done by the UA. This would allow 
scripts to add extra buffer margins e.g. if user has previously 
experienced buffer underruns while viewing other videos on the same site.

It might even make sense to support @preload with a numeric value 
without an unit as the count of kilobytes to preload. However, always 
requiring the unit would allow extending @preload with e.g. <video 
preload="5s"> in the future. I personally don't like specifying preload 
amount as seconds because it requires first loading metadata to compute 
the actual amount to preload. In addition, the preloaded amount seldomly 
matches any second amount but actual available data transfer bandwidth, 
video bitrate and audio bitrate needs to be considered for skipless 
playback.


[1] 
https://html.spec.whatwg.org/multipage/embedded-content.html#attr-media-preload

[2] http://www.stevesouders.com/blog/2013/04/12/html5-video-preload/

-- 
Mikko
Received on Friday, 27 March 2015 10:43:54 UTC

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