Sources for free AV sync test patterns? (ideally SD)

[Brad]

Wanna do some tests without building a test card video completely from scratch myself.

I have at least one BD with A/V sync tests, but I'd rather not have to use 16:9 for testing VHS workflows.

[jagabo]

A lot of THX certified DVDs include test patterns. I don't recall if there are any A/V sync tests. You could use AviSynth to generate ColorBars and overlay a graph of the audio.

ColorBars(width=720, height=576)
AssumeFPS(25)
AudioGraph(0)

Keep in mind that audio compression usually adds a delay of 10 to 30 milliseconds.

[Brad]

Sadly, no sync tests with THX discs.

ColorBars: I forgot that "The tone pulses in the right speaker, being turned on and off once every second." Thought it was a constant.

So I could overlay the AudioGraph in the burned video, capture it, run AudioGraph on the capture, and visually see any offset, yeah? I suppose Subtract + DelayAudio could be used to determine the number of ms? Assuming levels can be matched relatively closely...

Are there any industry-standard test patterns for automatically determining A/V offset values?

[jagabo]

So I could overlay the AudioGraph in the burned video, capture it, run AudioGraph on the capture, and visually see any offset, yeah?

Yes.

I suppose Subtract + DelayAudio could be used to determine the number of ms? Assuming levels can be matched relatively closely...

Yes. You can even use the horizontal position of the amplitude change to determine the delay. In my sample script the amplitude change happens at the start of a frame. Here' I added a 10 ms delay to the audio with DelayAudio(0.010):


[Attachment 41370 - Click to enlarge]

With a 25 fps video we know that the duration of each frame is 40 ms. You can see the audio change amplitude at about 1/4 the width of the frame, 40 * 1/4 = 10.

Are there any industry-standard test patterns for automatically determining A/V offset values?

I don't know.

[Brad]

Thanks!

Here' I added a 10 ms delay to the audio with DelayAudio(0.010) [...] With a 25 fps video we know that the duration of each frame is 40 ms. You can see the audio change amplitude at about 1/4 the width of the frame, 40 * 1/4 = 10.

Wow. Jealous of your math prowess.

[Brad]

Found this 29.97p test. Haven't looked at it closely enough to see whether it would be easier or more difficult to use than your idea.