Event message track sample files m59640.

[podborski]

2 files are not yet added (only their metadata).
It would be desirable to reduce the file size.

[cconcolato]

The flags for prft are:

- if flags is set to 0, the UTC time is the time at which the frame belonging to the reference
track in the following movie fragment and whose presentation time is media_time was input
to the encoder.
- if flags is set to 1, the UTC time is the time at which the frame belonging to the reference
track in the following movie fragment and whose presentation time is media_time was
output from the encoder.
- if flags is set to 2, the UTC time is the time at which the following MovieFragmentBox was
finalized. media_time is set to the presentation of the earliest frame of the reference track in
presentation order of the movie fragment.
- if flags is set to 4, the UTC time is the time at which the following MovieFragmentBox was
written to file. media_time is set to the presentation of the earliest frame of the reference
track in presentation order of the movie fragment.
- if flags is set to 8, the association between the media_time and UTC time is arbitrary but
consistent between multiple occurrences of this box in the same track
- if flags is set to 24 (i.e. the two bits corresponding to value 8 and 16 are set), the UTC time
has a consistent, small (ideally zero), offset from the real-time of the experience depicted in
the media at media_time

[podborski]

https://git.mpeg.expert/MPEG/Systems/FileFormat/isobmff/-/issues/329

[podborski]

@DenizUgur do you remember how we deal with associated files such as MPDs?

Unaccounted file: ../data/file_features/under_consideration/event_message/out_avail_track.mpd
Unaccounted file: ../data/file_features/under_consideration/event_message/avail_overlap.mpd

[DenizUgur]

As with any associated files, we add them to the relevant conformance files. If you don't want do deal with them, add their glob pattern to data/.cfignore. We get a warning for ignored files so they won't be lost.

[podborski]

@DenizUgur do you mind adding these 2 files?

[DenizUgur]

@podborski here you go, ready for merge