[Bug 23549] New: Clarify definition of decode timestamp

https://www.w3.org/Bugs/Public/show_bug.cgi?id=23549

            Bug ID: 23549
           Summary: Clarify definition of decode timestamp
           Product: HTML WG
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Media Source Extensions
          Assignee: adrianba@microsoft.com
          Reporter: watsonm@netflix.com
        QA Contact: public-html-bugzilla@w3.org
                CC: mike@w3.org, public-html-media@w3.org

Decode timestamp is an odd concept, since the time at which a frame is decoded
is implementation dependent and not visible externally. It is really only
decode order that needs to be externally specified. However, decode timestamp
is used throughout the specification as a proxy for decode order.

Also, the decode timestamp is not actually the time at which the frame needs to
be decoded, since in practice this would be too late (rendering of this frame
and decoding of dependent frames takes time).

Replace:

"Coded Frame
A unit of media data that has a presentation timestamp and decode timestamp.
The presentation timestamp indicates when the frame must be rendered. The
decode timestamp indicates when the frame needs to be decoded. If frames can be
decoded out of order, then the decode timestamp are present in the byte stream.
The user agent must run the end of stream algorithm with the error parameter
set to "decode" if this is not the case. If frames cannot be decoded out of
order and a decode timestamp is not present in the byte stream, then the decode
timestamp is equal to the presentation timestamp."

with

"Coded Frame
A unit of media data that has a presentation timestamp and decode timestamp.
The presentation timestamp indicates when the frame must be rendered.

_Decode Timestamp_

The decode timestamp indicates _the latest time at which_ the frame needs to be
decoded _assuming instantaneous decoding and rendering of this and any
dependent frames (this is equal to the presentation timestamp of the earliest
frame in presentation order that is dependent on this frame). If frames can be
decoded out of _presentation_ order, then the decode timestamps must be present
in _or derivable from_ the byte stream. The user agent must run the end of
stream algorithm with the error parameter set to "decode" if this is not the
case. If frames cannot be decoded out of _presentation_ order and a decode
timestamp is not present in the byte stream, then the decode timestamp is equal
to the presentation timestamp."

(emphasis added to changes)

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Received on Thursday, 17 October 2013 16:22:04 UTC