Re: Proposal: Remove canplaythrough event from audio/video tag

On Nov 1, 2011, at 3:10 PM, Victoria Kirst wrote:

>   - *What are some real examples of how canplaythrough is useful for a web
>   developer?* Even if it were 100% accurate, what is the benefit of the
>   event? Given that it's* not* 100% accurate and that the accuracy is
>   largely up to the discretion of the web browser, what is the benefit?

The purpose of the canplaythrough event (and of the HAVE_ENOUGH_DATA ready state) are to signal to the page
author that playback is likely to keep up without stalling.  This seems to me to have a fairly obvious
benefits.  

Here's a hypothetical scenario:

Assume a 100% accurate implementation of canplaythrough (in that the UA can predict with 100% accuracy at
what time in the future will the final byte of media data will be downloaded.)  Assume magic or time travel if necessary.

In this scenario, a <media> element with with a canplaythrough listener will always begin playing at the
earliest possible time and will never stall during normal playback. This is a clear benefit.

> The question I keep running into is *how inaccurate can the browser be
> until the event is no longer useful?*

This seems to be a Quality of Service issue.  Different UAs will have different implementations of
canplaythough at varying degrees of accuracy.  Some UAs will favor a lower possibility of stalling over an
earlier start time.  Others may cut closer to the margin-of-error and favor earlier start times.

> There are many ways to approximate download speed, but it quickly becomes
> complicated to maintain accuracy:
>