Overview
IEC TS 62644:2012 provides guidelines for time code transmission in professional video storage equipment that handle progressive video at 50 frames-per-second or 59.94 frames-per-second. The Technical Specification defines how Ancillary Time Code (ATC) (VITC payloads) must relate to an external reference signal when the system enforces a two-frame edit resolution by treating video frames as frame pairs. The goal is reliable synchronization and interoperability of storage devices, reference signals and time code under system operation.
Key topics and technical requirements
- Scope: Applies to storage equipment working with progressive 50 Hz or 59.94 Hz video and using an external reference signal to maintain frame-pair alignment.
- Frame pair concept: Time addresses increment only every other frame for the high frame rates, resulting in a two-frame edit resolution.
- Field mark flag usage: Recommended to identify frames within a pair - set to 0 for the first frame and 1 for the second frame (as conveyed in VITC/ATC).
- ATC payload types:
- ATC_VITC1 associated with the first frame of a pair (field mark flag = 0).
- ATC_VITC2 associated with the second frame of a pair (field mark flag = 1).
- Reference signal relationship:
- In normal-playback at recorded speed: reference signal field1 → ATC_VITC1 (flag 0); field2 → ATC_VITC2 (flag 1).
- During non‑standard playback speeds (e.g., slow motion, still), ATC packet timing and field mark flags may not align with reference fields; field flags may be 0 or 1 depending on play mode while preserving the time code associated with recorded content.
- Interoperability focus: Ensures consistent mappings between reference fields, ATC payloads and field mark flags across devices.
Applications and who uses it
IEC TS 62644:2012 is practical for:
- Manufacturers of professional video storage systems (disk recorders, servers, archive devices)
- Broadcast engineers and facility integrators designing synchronized multi-device systems
- Post-production houses and editors requiring accurate time-code alignment for editing/ingest
- Quality assurance teams validating time code transmission and sync behavior
Use cases include synchronization to external reference signals, maintaining consistent edit resolution, and ensuring ATC-based time code remains reliable during playback at varied speeds.
Related standards
Normative references that should be consulted with IEC TS 62644:
- SMPTE ST 12-1:2008 (Time and Control Code)
- SMPTE ST 12-2:2008 (Transmission of Time Code in the Ancillary Data Space)
- SMPTE ST 318:1999 (Reference Signals for 59.94/50 Hz systems)
- SMPTE ST 274:2008 (Digital timing/reference sequences)
- IEC 60461 (Time and control code)
Keywords: IEC TS 62644:2012, professional video storage equipment, time code transmission, Ancillary Time Code, ATC_VITC1, ATC_VITC2, reference signal, frame pair, 50 fps, 59.94 fps, progressive video, field mark flag.