2009/4/7 Philip Jägenstedt <[email protected]>: > On Tue, 07 Apr 2009 06:11:51 +0200, Chris Double <[email protected]> > wrote: > >> On Tue, Apr 7, 2009 at 3:40 AM, Eric Carlson <[email protected]> >> wrote: >>> >>> Media time values are expressed in normal play time (NPT), the absolute >>> position relative to the beginning of the presentation. >> >> I don't see mention of this in the spec which is one of the reasons I >> raised the question. Have I missed it? If not I'd like to see the spec >> clarified here. >> >> Chris. > > Indeed clarification is needed. In my opinion time 0 should correspond to > the beginning of the media resource, no matter what the timeline of the > container format says. This means that currentTime doesn't jump when > playback begins and never goes beyond duration. > > Taking Ogg as an example, there's no requirement that the granulepos start > at zero nor does a non-zero granulepos imply any special semantics such as > "the beginning of the file has been chopped off". A tool like oggz-chop > might retain the original granulepos of each packet or it could just as well > adjust the stream to start at granulepos 0. Neither is more correct than the > other, so I'd prefer we not try to infer anything from it, especially since > such low-level timing information might be hidden deep inside the platform > media framework (if it normalizes the time like XiphQT presumably does). > > Perhaps we would like to have some way to express where a resource is > positioned on a timeline external to the resource itself, but could SMIL do > this perhaps?
For Ogg, the start time of the original file (prior to chopping) is recorded in the skeleton headers by oggz-chop, so this info is intrinsically in the media format itself. cheers, Conrad.
