Presentation timestamp cadence

MISB ST 1402.2 §7.3 limits the difference between successive coded PTS values to 0.7 seconds for each elementary stream. PTSCadenceValidator applies that rule directly to the PESStreamEvent objects emitted by the demuxer:

from stanag4609 import PESStreamEvent, PTSCadenceValidator

validator = PTSCadenceValidator()

for event in demuxer.feed(transport_chunk):
    if isinstance(event, PESStreamEvent):
        for issue in validator.observe(event):
            log.error(issue.message)

The exact 0.7-second boundary passes; one additional 90 kHz tick fails. State is isolated by program and PID. The comparison uses the shortest signed distance across the 33-bit PTS rollover, so rollover and modest presentation- order reordering do not look like multi-hour gaps. An adaptation-field discontinuity or a changed stream type on a reused PID starts a new baseline.

PES packets without PTS do not themselves establish a successive-PTS pair. The separate H.222.0 §2.7.5 rule requires a PTS for the first access unit of every elementary stream. VideoAccessUnitPTSValidator recognizes the mandatory transport access-unit markers for MPEG-1/2 Video, AVC/H.264, and HEVC/H.265 while retaining only three bytes per stream:

from stanag4609 import PESStreamEvent, VideoAccessUnitPTSValidator

video_pts = VideoAccessUnitPTSValidator()

for event in demuxer.feed(transport_chunk):
    if isinstance(event, PESStreamEvent):
        for issue in video_pts.observe(event):
            log.error(issue.message)

for issue in video_pts.finish():
    log.error(issue.message)

Start-code prefixes split across PES packets are attributed to the PES that contains their first byte. A transport discontinuity starts a new baseline, because §2.7.5 also requires PTS on the first access unit after a decoding discontinuity. The verifier applies the same rule to reconstructed Layer II and AAC-LC audio frames.

The same clause permits a video PTS only when the PES packet contains the first byte of a picture or access unit. A PTS-bearing PES with no complete marker is held for at most three subsequent payload bytes, allowing a split start code to complete without a false error. Once disproved—or at finish() for a finite capture—it is reported as st1402.pts.pts_without_access_unit.

ST 1402.2 labels “PTS on every Motion Imagery frame” as a MISB usability recommendation, not a mandatory conformance requirement. H.222.0 also has conditional rules and explicit exceptions for later AVC access units, still pictures, and very-low-frame-rate AVC with timing information. The library does not turn the recommendation into an error and does not yet claim the full conditional AVC timing model.

FMVVerifier runs this check automatically and reports an error such as st1402.pts.interval or st1402.pts.first_access_unit with the program, PID, source offset, and requirement citation.