[whatwg] HTML5 video: frame accuracy / SMPTE

Glenn Maynard glenn at zewt.org
Fri Jan 21 17:58:20 PST 2011

Regarding whether to use "fast" or "accurate" seeks by default, it
seems like a balance between the frequency of use cases for each, the
likelihood of either default being wrong, principle of least surprise,
and consistency with other APIs.  Looking at various seek use cases:

Seek bars should use "fast", particularly for longer videos and videos
with keyframes spaced far apart.  Videos encoded to allow quick
seeking by using frequent keyframes, on the other hand, might use
"accurate" even for seek bars.

Chapter seeking should use "accurate".  If a chapter is at 1h45m12.2s,
a fast seek would end up seeking into the previous scene, or into the
middle of a fade-out.

User-specified seeks, like YouTube's "tm" URL parameter, should be
"accurate", for the same reason as chapters.

A "seek ahead by N seconds" button should use "accurate".

Even in the primary use case of a seek bar, it's not always wanted.

The consequences of using "fast" as the default, when people forget to
explicitly specify "accurate", seem worse than the other way around.
I recommend "accurate" as the default.

Glenn Maynard

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