Troubleshoot increasing audio delay with SDI-embedded audio
When you capture SDI-embedded audio through the Core Audio driver of a video I/O device, the audio can drift progressively out of sync, with the delay increasing over time. This article explains why this happens and which steps reduce or avoid the delay. It relates to the articles Working with audio and Setting up AJA video I/O devices.
Symptom#
The embedded audio is in sync at first but becomes increasingly delayed against the video over the course of a session. The delay does not reset on its own and affects both live monitoring and recordings made while it is present.
Cause#
The delay increases each time the incoming camera signal enters a no-signal condition or switches its video format. Each of these events is handled by the video I/O device’s Core Audio driver and adds to the accumulated audio delay.
This is not limited to physically unplugging a cable. Wireless systems such as Teradek Bolt can briefly change or drop their output format during camera repositioning, battery swaps, or short dropouts, which has the same effect.
Solution 1: Set a fixed video format on the AJA device#
Because the delay accumulates from no-signal conditions and format switches, keeping the input signal stable is the most effective mitigation. Set a fixed video format on the AJA device instead of “Auto” so the device maintains a continuous output through brief dropouts and format changes.
For the full steps, see Troubleshooting intermittent video signal loss when using Teradek wireless systems with AJA I/O devices.
Solution 2: Use an independent audio path#
A class-compliant USB audio interface provides a separate Core Audio device that is independent from the SDI video format. Because it is not tied to the state of the video signal, it is not affected by this behavior. Connect a class-compliant USB audio interface, such as a Focusrite Scarlett, as a separate audio input device and select it in Reeltime’s audio settings as described in Setting up audio I/O interfaces.