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Understanding TVIs: notes & examples

Understanding TVIs: notes & examples All TDSs that are associated with a TVI are considered to be alternative "representations" of the same time-based "information".

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Understanding TVIs: notes & examples

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  1. Understanding TVIs: notes & examples All TDSs that are associated with a TVI are considered to be alternative "representations" of the same time-based "information". That is, all these TDSs are considered to be conveying the same "message" (the same "information" with the same relationship to time).

  2. Example 1a MXF File, 50Hz video, VC-2. This TDS uses Time Context A. Time count=0, time_unit=1/50 Quicktime File, 25Hz video, H.264. This TDS uses Time Context A. Time count=0, time_unit=1/25 Both of these TDSs are associated with the same TVI (TVI 1). Both TDSs use the same Time Context (Time Context A).

  3. Example 1b MXF File, 50Hz video, VC-2. This TDS uses Time Context B. Time count=350, time_unit=1/50 Quicktime File, 25Hz video, H.264. This TDS uses Time Context A. Time count=0, time_unit=1/25 Both of these TDSs are associated with the same TVI (TVI 1). These two TDSs use different Time Contexts but the relationship between these Time Contexts is known (specifically: a Time Value of [count=350, time_unit=1/50] in Time Context B occurs at the same point in time as the zero-point in Time Context A).

  4. Example 2 “Live” TDS produced during News Channel playout, 25Hz video, H.264. Time count=1520964037000000000, time_unit=1/10^9 (2018-03-13T18:00:00Z) In the above TDS the Time Values are PTP-derived. The TDS uses Time Context C (in which a count of zero is defined to occur at 1 January 1970 00:00:00 TAI). The above TDS is associated with TVI 2. TVI 2 is different to TVI 1. We record this live output into a file. Quicktime File, 25Hz video, H.264. First frame at “0” BUT we also record, as extra metadata (inside or outside the file), that this TDS uses Time Context D (in which a count of zero is defined to occur at 2018-03-13T18:00:00Z). This TDS is associated with TVI 2 – this is the SAME TVI AS ABOVE. Time count=0, time_unit=1/25 (2018-03-13T18:00:00Z)

  5. In Example 2, two TDSs are associated with the same TVI. These TDSs use different Time Contexts. That is fine because we know the mapping between those Time Contexts. Whenever TDSs are associated with a TVI they must either all use the same Time Context or the mapping between their Time Contexts must be known.

  6. Example 3 In this TDS, the Time Value coupled with each video frame (Data Object) is the time at which the light hit the camera’s sensor Time count=1520733000000000111, time_unit=1/10^9 In this TDS, the Time Value coupled with each video frame (Data Object) is the time the video frame left the camera’s network interface Time count=1520733000000000111, time_unit=1/10^9 In this TDS, all Time Values have been increased by a constant amount so that the video aligns with an audio signal Time count=1520733000000000111, time_unit=1/10^9 These three TDSs: all use the SAME Time Context; are all associated with DIFFERENT TVIs. The video frames (Data Objects) are the same in each TDS; but in each TDS the relationship with time is different and so the TDSs are associated with different TVIs.

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