Add taic, itai timestamp boxes

[farindk]

This is work in progress, but ultimatively add ‘taic’ & ‘itai’ boxes which provide support for nano-precision timestamps.

[farindk]

taic uses a float32 value. Where is it defined how that value is stored in the file (little-endian / big-endian)?
Have you considered using an integer value for this in the standard?

[farindk]

Another point: I'd like to remove status_bits from heif_property_set_tai_timestamp(). If I read the spec correctly, timestamp_validity can be derived from TAI_timestamp (see my comments to the specs).
synchronization_status should be an extra parameter. It is the responsibility of the library to put this into the correct bits. That's exactly what should be transparent to the user.

Am I correct with the first assumption? Can we derive timestamp_validity from TAI_timestamp==0xFFFF....FFFF ?

[bradh]

taic uses a float32 value. Where is it defined how that value is stored in the file (little-endian / big-endian)?

It should (currently) be double(32) which is a big-endian value (see ISO 14496-1:2010 Section 8.2.2 - "most significant byte first").

Apparently there is a new part (-34) that will clarify the syntax, by codifying all the inconsistencies as normative. That will make double an obsolete alias and introduce float(32). See https://www.mpeg.org/structure/systems/ (https://www.mpeg.org/wp-content/uploads/mpeg_meetings/143_Geneva/w22951.zip for the draft)

Have you considered using an integer value for this in the standard?

Seems reasonable to me.