Overview
ISO/IEC 13818-9:1996 specifies a Real Time Interface (RTI) extension for systems decoders that receive Transport Streams. It does not change or supersede any requirements in ISO/IEC 13818-1; all Transport Streams must still comply with Part 1. Part 9 defines timing, clock/PCR relationships, buffer-sizing adjustments, and conformance tests so that decoders with an RTI can operate correctly when fed real-time-delivered stream bytes.
Key topics and technical requirements
- Real-Time Interface Decoder (RTD) model: a conceptual decoder model used to state RTI timing and buffer requirements. The RTD is based on the T-STD model from ISO/IEC 13818-1 but replaces the T-STD byte schedule with actual byte arrival times and adds RTI-specific constraints.
- PCR accuracy and timing: defines the relationship between Program Clock Reference (PCR) values and the arrival time of the bytes that carry them. A system clock counter and a bounded arrival-time error (tjitter) are required so PCRs map to receiver clock time within the specified jitter bounds.
- Clock frequency and slew: system clock frequency accuracy and slew-rate limits from Part 1 are mandatory for RTI. Practical conformance checks use typical bounds referenced in the standard (for example, frequency error and small slew limits are considered during testing).
- Buffer sizing: RTD buffer sizes (transport buffer, smoothing, multiplex and decoder buffers) are increased relative to T-STD sizes to account for arrival jitter. Formulas in the standard add terms proportional to tjitter × data rate (plus packet overhead) to ensure no under/overflow.
- Low-Jitter profile (RTI-LJ): a defined RTI profile for low-jitter applications uses tjitter = 50 microseconds; decoders claiming RTI-LJ must handle any stream meeting that jitter bound.
- Compliance testing methods:
- Plot PCR (converted to time) versus PCR arrival time: inspect slope (frequency error), curvature (slew), and horizontal scatter (jitter).
- Approximate tests: Diverging Lines and Parallel Lines tests using frequency-error bounds (e.g., ±30 ppm) and horizontal separation = tjitter.
- Buffer occupancy tests adapted from T-STD to RTD arrival times and buffer sizes.
Applications and who uses it
- Broadcast equipment designers and systems decoder manufacturers implement RTI timing and buffering to ensure real‑time playback interoperability.
- Set-top box and receiver integrators use RTI constraints to design interfaces between data-link adaptors and decoders.
- Test laboratories and quality assurance engineers employ the RTI conformance tests (PCR vs arrival analysis, buffer tests) to validate stream delivery and decoder behavior.
- Service operators and system architects use RTI profiles (e.g., RTI-LJ) to specify interoperability limits for low-jitter delivery systems.
Related standards
- ISO/IEC 13818-1 (Systems) - foundational Transport Stream, T-STD model and normative requirements referenced throughout Part 9.