Comments on clause 2.4

[haudiobe]

https://dashif-documents.azurewebsites.net/Events/master/event.html#timed-metadata-timing

An alternative way to convey information relating to a media is using timed metadata tracks. Timed metadata tracks are ISOBMFF formatted tracks that obey the following characteristics:

We need a reference for this. Are these requirements from DASH-IF? Where do they come from? We need a clear definition on how we can use timed metadata tracks.

2. the the Handler Box hdlr has handler_type set to meta to signal the fact that the track contains metadata

duplicated "the". Is this a definition or a requirement?

3. the null media header nmhd is used in the minf box

Is this a definition or a requirement?

4. contain metadata (non media data relating to presentation) in embedded in ISOBMFF samples

Where does this come from and what does it mean?

Figure 7 is referenced as Figure 4

In Figure 7 it is unclear what all of this means. What is Sample Arrival Time and Segment's earliest sample presentation time. The figure is confusing for me.

Also one or more metadata samples are included in a segment with Segment start time (AT).

At the start of the segment, the must be a metadata sample. The whole setup is confusing or are you assuming that the metadata track is carried multiplexed with video?

Note that the metadata sample duration can not go beyond fragment duration for fragmented metadata tracks, i.e. to the next fragment. In the case of CMAF, the same constraints are maintained for CMAF Chunks.

CMAF chunks are ISO BMFF fragments. We should remove the second sentence.

In this document, we use the following common variable names instead of some of above variables to harmonize parameters between Inband events, MPD events, and timed metadata samples:

scheme_id = timed metadata track URI , signalled in URIBox in URIMetaSampleEntry

timescale = timed metadata track timescale in mdhd box.

presentation_time = timed metadata sample presentation time/timescale

duration = timed metadata sample duration/timescale

message_data = timed metadata sample data in mdat

Is this the mapping to the common structure? We should be very explicit about this

[irajs]

Added the reference.

Improved the text to be more clear about requirements coming from ISOBMFF.

Improved the language on AT.

The common variables are not common structures. Improved the language to avoid confusion.

[haudiobe]

(Event TF - 19/10/04) Check implementation, if no further comments, will closed at next Event TF.