How to measure audio / video delay?

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Viktor Laga

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  • Joined: Sat May 25, 2013 1:46 pm

How to measure audio / video delay?

PostWed Aug 21, 2013 4:11 pm

Hello!

My current setup includes a some consumer HDMI cameras, HDMI2SDI converters connected to a ATEM TV Studio. The audio signal is fed separately into the ATEM TVS using a Behringer DEQ2496 unit.

To determine a delay between the audio and video signal I recorded a short clip using a) MXLight and b) a sep. HDMI recording box. The video was shot with a camera, the audio equipment involved and a clapper application on an iPad.

The resulting clip (MP4 container) I imported to FinalCutProX (FCPX). There I could "see" a video delay with roughly 200ms. Adding this delay to the DEQ2496 didn't change much in an additional run. FCPX again came up with roughly 200ms delay.

To verify the results I compared audio and video with avidemux2 and Audacity, there I could determine a delay of about 90msec for the first run.

Additionally I converted the MP4 file to ProRes (using ffmepeg). Comparing MP4 and ProRes file showed different results in FCPX.

Questions:

    Is FCPX doing some "magic" with the audio when importing MP4 files and therefore falsifying my approach?

    Are there any other suggestions how to measure / determine a potential delay?

Thanks for your support.

LagaV
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Liam Kennedy

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  • Location: Pasadena, CA

Re: How to measure audio / video delay?

PostWed Aug 21, 2013 5:23 pm

The published delay as per Blackmagic for non-genlocked sources is 1 frame. So calculate that based upon whatever video standard you are working with on the TVS. 200ms is WAY WAY to much. Something is going wrong with some part of your workflow to measure the delay.

In my tests I both record in camera - and then record direct from the ATEM via my hyperdeck. That makes it a lot simpler to measure the delay as I have a direct comparison.
ATEM 1/ME, TVS, Hyperdeck Studio, Fujitsu Lifebook NH751 USB3

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