[whatwg] HTML5 video: frame accuracy / SMPTE

Chris Pearce chris at pearce.org.nz
Tue Jan 11 17:17:38 PST 2011

On 12/01/2011 1:37 p.m., Dirk-Willem van Gulik wrote:
> On 11 Jan 2011, at 23:00, Chris Pearce wrote:
>>> Even then I'd like the 'virtual' FPS of the WebM file exposed to the
>>> webbrowser- similar to how my other utilities report a FPS.
>> If the 'virtual' FPS value isn't provided by the container, and given that the frame durations could potentially have any distribution and that the media may not be fully downloaded, how can this be effectively calculated?
> I cannot think of a format where this would in fact be the case - but for a few arcane ones like an animated push gif without a loop.

WebM can be variable frame rate. At best the WebM container 
specification [http://www.webmproject.org/code/specs/container/#track] 
lists the FrameRate block as "Informational only", which presumably 
means the value stored in the container can't be trusted.

Chris P.

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