sandersaares
commented
4 years ago MPDs are not dynamic. Media Presentations are. MPDs are updated at the server and clients need to request those at appropriate time. DASH provides a model that does MPD updates only if anything changes.
Agreed. Text updated accordingly.
This is unclear. Please check clause 4.2 and 4.4 for the details on MPD updates
Not sure what the comment is about (what is unclear). Regardless, the text has gone through another iteration and is hopefully even more understandable now. Please re-check and post additional comments if you find confusion remains.
this is not correct as it is unclear what time refers to
The text has been adjusted to more explicitly reference wall clock time. Hopefully this eliminates the confusion.
I close the issue as I believe the comments are addressed in more recent iterations (visible in GitHub but not in the HTML yet, as I did not want to update the version undergoing community review).
5.5.1. MPD refreshes Dynamic MPDs may be updated as the content of the presentation changes.
MPDs are not dynamic. Media Presentations are. MPDs are updated at the server and clients need to request those at appropriate time. DASH provides a model that does MPD updates only if anything changes.
In order to stay informed of the updates, clients need to perform MPD refreshes at appropriate moments to download the updated MPD snapshots.
This is unclear. Please check clause 4.2 and 4.4 for the details on MPD updates
Clients presenting dynamic MPDs SHALL execute the following MPD refresh logic:
When an MPD snapshot is downloaded, it is valid for the present moment and at least MPD@minimumUpdatePeriod after that.
this is not correct as it is unclear what time refers to
A client can expect to be able to successfully download any media segments that the MPD defines as available at any point during the MPD validity duration.
The clients MAY refresh the MPD at any point. Typically this will occur because the client wants to obtain more segment references or make more media segments (for which it might already have references) available by extending the MPD validity duration.
This may result in a different MPD snapshot being downloaded, with updated information.
Or it may be that the MPD has not changed, in which case its validity period is extended to now + MPD@minimumUpdatePeriod.
Note: There is no requirement that clients poll for updates at MPD@minimumUpdatePeriod interval. They can do so as often or as rarely as they wish - this attribute simply defines the MPD validity duration.
Services MAY publish in-band events to explicitly signal MPD validity, instead of expecting clients to regularly refresh on their own initiative. This enables finer control by the service but might not be supported by all clients.
For more details, see §7.6 Dynamic MPDs and §10.7 Update signaling via in-band events.