[whatwg] HTML5 video: frame accuracy / SMPTE

Rob Coenen coenen.rob at gmail.com
Tue Jan 11 13:58:19 PST 2011

Intresting- I didn't know that variable frame-rate videos were actually
being used for HTML5 video.

But still- the vast majority of all video uses a fixed frame rate- ever
since Eadweard Muybridge invented 'motion picture' back in 1878.

For example, most hardware these days record in SMPTE compliant MPEG4
format, meaning that they do use timecoded encoding- and thus have a fixed
frame-rate or FPS.

All the video files on my laptop have a fixed frame-rate and the FPS
property can be easily figured out with any media related tool on desktop or

So why not expose the FPS property as meta-data to the web browser alongside
the 'duration' property?


On Tue, Jan 11, 2011 at 9:29 PM, Eric Carlson <eric.carlson at apple.com>wrote:

> On Jan 11, 2011, at 12:54 PM, Rob Coenen wrote:
> Eric, not sure if I understand what you mean. Are you referring to
> digitally encoded files where frame #1 has a different duration than frame
> #2?
>   Exactly, every frame can have an arbitrary duration so "frame rate" may
> have no meaning. Even in the case of video captured from film, the original
> frame rate is often not stored in the digital file so there is no way to
> programmatically determine the original frame rate.
> eric
> On Tue, Jan 11, 2011 at 6:10 PM, Eric Carlson <eric.carlson at apple.com>wrote:
>> On Jan 11, 2011, at 9:54 AM, Rob Coenen wrote:
>> > just a follow up question in relation to SMPTE / frame accurate
>> playback: As
>> > far as I can tell there is nothing specified in the HTML5 specs that
>> will
>> > allow us to determine the actual frame rate (FPS) of a movie? In order
>> to do
>> > proper time-code calculations it's essential to know both the
>> video.duration
>> > and video.fps - and all I can find in the specs is video.duration,
>> nothing
>> > in video.fps
>> >
>>   What does "frames per second" mean for a digitally encoded video file,
>> where frames can have arbitrary duration?
>> eric

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