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SMPTE 2022-7

Interface

When users select the ST2022-7 comparison, they can select the pcap file and the stream within that pcap file that will be the reference stream, as well as the stream that will be compared with it. When the processing is complete, users can view the comparison by selecting it from the list on the bottom of the page.

The comparison page shows the information about each stream, as well as the outcome of the comparison.

There are five summary values. The first two of them refer to the amount of data that is present in the selected streams:

Parameter Explanation
Total The number of packets in both streams.
Overlap The number of packets that overlap in both streams. That is, if one of the captures started earlier in time than the other, those initial packets will not overlap the others.

The remaining values refer to the result of the comparison of the overlapping packets:

Parameter Explanation
Different packets The number of packets that are present but which content is not exacly the same in both streams.
Missing The amount of packets that exist in one stream but are absent from the others.
Equal The number of packets that are exactly equal in both streams.

Algorithm

The first step of the algorithm is to determine the intersection of both streams. This is done using RTP timestamps. Given:

Parameters Explanation
Tfa, Tfb The first RTP timestamps of stream A and stream B.
Tla, Tfb The last RTP timestamps of stream A and stream B.

Then:

Parameter Explanation
Initial timestamp Ti Equal to max(Tfa, Tfb)
Final timestamp Tf Equal to min(Tla, Tlb)

Therefore, only packets with RTP TS between Ti and Tf will be accounted for in the comparison.

Then, the algorithm compares each packet with the same timestamp in both streams:

  • If one packet is missing from one of the streams, it is counted as a missing packets;
  • If one packet is present in both streams but the content is different, it is counted as a different packet.
  • If one packet is present in both streams and the content is exactly the same, it is counted as an equal packet.

The content comparison is made over the whole UDP payload, including the RTP header and the RTP payload.