PCR (Program Clock Reference) is the timing heartbeat of an MPEG transport stream. The encoder periodically inserts a snapshot of its 27 MHz system clock into the stream, and the decoder locks its own clock to those samples, recovering the exact timebase the content was created on. This matters because the PTS and DTS timestamps that schedule each audio and video frame are only meaningful relative to that shared clock — without PCR the decoder would slowly drift and audio and video would separate. PCR is delivered frequently and accurately, because jitter in its values becomes jitter in playback timing and ultimately lip-sync error.
The book · Volume 5 of 7
Audio for Video: A Complete Guide to Sound in Video Products: From Jitter Buffers and Lip Sync to Atmos, Quality Metrics, and Neural Codecs
PCR is the clock a decoder locks to in MPEG-TS, and jitter or gaps in it show up as audio drift, lip sync errors and decoder glitches. Volume 5 covers it in detail with timestamps and clock domains, lip sync, and diagnosing incidents by symptom, so you can trace a timing fault in a transport stream to its source. Written by Nikolay Sapunov, CEO at Fora Soft.
Broadcast or IPTV streams drifting out of sync, and you suspect PCR jitter?
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