[whatwg] Start position of media resources

David Singer singer at apple.com
Thu Apr 30 09:22:25 PDT 2009

At 6:21  +0000 30/04/09, Ian Hickson wrote:
>On Thu, 30 Apr 2009, Robert O'Callahan wrote:
>>  On Thu, Apr 30, 2009 at 1:04 PM, Ian Hickson <ian at hixie.ch> wrote:
>>  >
>>  > I have left the spec as is (except for adding startTime), which means
>>  > that currentTime can be greater than duration if startTime is not
>>  > zero.
>>  I think it would be safer to have the invariant that 0 <= currentTime <=
>>  duration. Most resources will probably have startTime==0 so authors will
>>  write scripts expecting these invariants, and their scripts will break
>>  when confronted with unusual resources with startTime>0.
>>  So I think a safer design would be to interpret currentTime as relative
>>  to the startTime, perhaps renaming startTime to 'timeOffset' instead?
>I considered that, but it seems that in the streaming video ("DVR-like")
>case, in the steady state where the data in the buffer is being thrown
>away at the same rate as the video is being played you'd end up in a weird
>position of the currentTime not changing despite the video playing, which
>would likely be even more confusing.

If the resource is 'seekable' then time is relevant, and I agree that 
time should be a normal play time and run from 0 to duration.

If it's not seekable (live), then the UA is free, of course, to 
buffer and allow seeking in that buffer, but that's a UA thing. 
Duration is indefinite, and the origin value of current time is also 
David Singer
Multimedia Standards, Apple Inc.

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