Bluish Coder

Programming Languages, Martials Arts and Computers. The Weblog of Chris Double.


2010-09-15

Changes to Firefox Video Implementation

I mentioned in my previous post about the Firefox video implementation that some changes were going to be made to make our implementation more spec compliant. These have now landed and will be in Firefox 4. The relevant bugs are:

  • Bug 571822 - Fire timeupdate less frequently than once per frame
  • Bug 584615 - Make media progress events be simple events

Prior to these landing we would try to fire a 'timeupdate' event every time a video frame changed. This allowed JavaScript applications to listen to this event and do things (like display subtitles) at fairly accurate time intervals. Unfortunately other browsers fire this event at different rates, usually with about 200ms between events. This made applications non-portable across browsers if they relied on per-frame events. As a result we've moved to firing 'timeupdate' no more frequently than 250ms. If you need to process time changes more often than this then it's best to use 'setTimeout' or 'setInterval' to query 'currentTime' at the rate you need. This will work across all browsers that support the media API.

The other change was to remove the 'progress' information from the 'progress' events. This was driven by a spec change. The 'progress' events used to contain additional information about the byte position and total number of bytes for the download. This additional information has been removed from the spec and we were the only browser that implemented that part. To prevent cross browser issues we've removed the information too. The alternative is to use the 'buffered' attribute on the media element and work with time data. 'buffered' support was also landed recently which is why we can now remove the non-compliant 'progress' event data.

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