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Sep 12, 2022
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Explain what a time scale is. #298

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Explain what a time scale is.
markafoltz Sep 9, 2022
ee50420
Update per comment by tidoust@.
markafoltz Sep 12, 2022
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38 changes: 23 additions & 15 deletions index.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -1003,6 +1003,16 @@ must send a [=presentation-connection-open-response=] message and
[=presentation-change-event=] messages when required.


Representation Of Time {#time-representation}
======================

The [[#remote-playback-protocol]] and the [[#streaming-protocol]] represent
points of time and durations in terms of a [=time scale=]. A <dfn>time
scale</dfn> is a common denominator for time values that allows values to be
expressed as rational numbers without loss of precision. The [=time scale=] is
represented in hertz, such as 90000 for 90000 Hz, a common time scale for
video.

Remote Playback Protocol {#remote-playback-protocol}
========================

Expand Down Expand Up @@ -1517,9 +1527,7 @@ changed.

All times, time ranges, and durations (such as position, duration, and
seekable-time-ranges) used above use a common [=media-time=] value (see Appendix A)
which includes a time scale. This allows time values which work on different
time scales to be expressed without loss of precision. The scale is represented
in hertz, such as 90000 for 90000 Hz, a common time scale for video.
which includes a [=time scale=].

<div class="note">
<table>
Expand Down Expand Up @@ -1792,7 +1800,7 @@ Each audio encoding offered defines the following fields:
RFC 6381 [=codecs parameter=].

: time-scale
:: The time scale used by all audio frames. This allows senders to
:: The [=time scale=] used by all audio frames. This allows senders to
make audio-frame messages smaller by not including the time scale
in each one.

Expand All @@ -1813,7 +1821,7 @@ Each video encoding offered defines the following fields:
:: The name of the codec used by the encoding.

: time-scale
:: The time scale used by all video frames. This allows senders to
:: The [=time scale=] used by all video frames. This allows senders to
make video-frame messages smaller by not including the time scale
in each one.

Expand All @@ -1839,7 +1847,7 @@ Each data encoding offered defines the following fields:
:: The name of the data type used by the encoding.

: time-scale
:: The time scale used by all data frames. This allows senders to
:: The [=time scale=] used by all data frames. This allows senders to
make data-frame messages smaller by not including the time scale
in each one.

Expand Down Expand Up @@ -1919,21 +1927,21 @@ separate QUIC streams.
:: Identifies the media encoding to which this audio frame belongs. This can be
used to reference fields of the encoding (from the
[=audio-encoding-offer=] message) such as the codec, codec properties,
time scale (aka clock rate), and default duration.
[=time scale=], and default duration.
Referencing fields of the encoding through the encoding id
helps to avoid sending duplicate information in every frame.

: start-time
:: Identifies the beginning of the time range of the audio frame. The
end time can be inferred from the start time and duration. The
time scale is equal to the value in the `time-scale` field of the
[=time scale=] is equal to the value in the `time-scale` field of the
[=audio-encoding-offer=] message referenced by the `encoding-id`.

: duration
:: If present, the duration of the audio frame. If not present, the
duration is equal to the `default-duration` field of the
[=audio-encoding-offer=] message referenced by the `encoding-id`.
The time scale is equal to the value in the `time-scale` field of
The [=time scale=] is equal to the value in the `time-scale` field of
the [=audio-encoding-offer=] message referenced by the `encoding-id`.

: sync-time
Expand Down Expand Up @@ -1966,7 +1974,7 @@ ending at the last dependent frame.
: encoding-id
:: Identifies the media encoding to which this video frame belongs.
This can be used to reference fields of the encoding such as the
codec, codec properties, time scale, and default rotation.
codec, codec properties, [=time scale=], and default rotation.
Referencing fields of the encoding through the encoding id helps
to avoid sending duplicate information in every frame.

Expand All @@ -1985,12 +1993,12 @@ ending at the last dependent frame.
: start-time
:: Identifies the beginning of the time range of the video frame. The
end time can be inferred from the start time and duration. The
time scale is equal to the value in the `time-scale` field of the
[=time scale=] is equal to the value in the `time-scale` field of the
[=video-encoding-offer=] message referenced by the `encoding-id`.

: duration
:: If present, the duration of the video frame. If not present, that
means duration is unknown. The time scale is equal to the value
means duration is unknown. The [=time scale=] is equal to the value
in the `time-scale` field of the [=video-encoding-offer=] message
referenced by the `encoding-id`.

Expand Down Expand Up @@ -2026,7 +2034,7 @@ that makes sense for a specific type of data.
: encoding-id
:: Identifies the data encoding to which this data frame belongs. This can be
used to reference fields of the encoding such as the type of data and
time scale. Referencing fields of the encoding through the encoding id
[=time scale=]. Referencing fields of the encoding through the encoding id
helps to avoid sending duplicate information in every frame.

: sequence-number
Expand All @@ -2037,14 +2045,14 @@ that makes sense for a specific type of data.
: start-time
:: Identifies the beginning of the time range of the data frame. The
end time can be inferred from the start time and duration. The
time scale is equal to the value in the `time-scale` field of the
[=time scale=] is equal to the value in the `time-scale` field of the
[=data-encoding-offer=] message referenced by the `encoding-id`.

: duration
:: If present, the duration of the data frame. If not present, the
duration is equal to the `default-duration` field of the
[=data-encoding-offer=] message referenced by the `encoding-id`.
The time scale is equal to the value in the `time-scale` field of
The [=time scale=] is equal to the value in the `time-scale` field of
the [=data-encoding-offer=] message referenced by the `encoding-id`.

: sync-time
Expand Down