ST 2110-30 Level Mismatch – Symptom Reconciliation

Symptom

Video is present and stable, but audio is silent.

Probable Cause

ST 2110-30 Level Mismatch — the audio stream packetization timing does not match what the receiver expects.

What This Actually Means

In SMPTE ST 2110, video (2110-20) and audio (2110-30) are transported as separate RTP streams. Because of this:

• Video can decode correctly even if audio fails.
• Audio receivers are sensitive to packet time (ptime) and framing.
• A mismatch in packet time results in audio being ignored or muted.

Why Video Works but Audio Doesn’t

• Video streams use different timing and buffering rules (less sensitive to ptime mismatch).
• Audio decoders expect strict packet intervals (e.g., 1 ms).
• If packet timing is wrong, audio packets are dropped or not decoded.

Diagnostic Step

Match Packet Time (ptime)

• Baseline: 1 ms packet time (common for ST 2110-30 audio)
• Verify sender and receiver configurations match
• Check SDP parameters such as:
  • ptime
  • maxptime
  • Sampling rate (e.g., 48 kHz)
  • Channel count

Key Insight

A 2110-30 Level Mismatch is not about signal strength, but about timing alignment of audio packets. Even small deviations from the expected packet interval (such as 125 µs vs 1 ms grouping) can result in complete audio silence while video remains unaffected.

Resolution

• Set both transmitter and receiver to the same packet time (typically 1 ms)
• Ensure SDP advertised values match actual stream behavior
• Restart or reinitialize the stream after changes