Solved Audio goes out of sync when I put a background on chroma key

Hi, I am new and grateful to be here for help. (Thanks for your tutorials on youtube.)

I have done a video with green screen, then removed the green with chroma key. Twice now, I have found the audio out of sync:

1. I readjusted the cropping on the chroma key and then the audio when out of sync and would not return to normal when I undid my change.
2. On another segment, all was in sync until I put a simple background .jpg behind it. I can position the .jpg so that I play the video with no background and all is fine in the audio. When I come to the segment with background, it goes out of sync and then returns to sync when the playback passes the background.

Thanks for your help,
Pamela

You sent private messages to me about the same question, so now your email inbox is going to be full of duplicate messages.
The last private message you sent to me, suggested that you had discovered the problem.

Depending on how powerful your computer is, adding Video FX like Chroma Key will slow the preview window down in real time and cause video lag. This is normal behaviour. While editing a video that is being used in a Chroma Key sequence, I often Mute the background chroma key video until I am finished editing, then the playback will be much smoother.

I suggest you read and watch this tutorial here for more tips:
www.moviestudiozen.com/free-tutorials/sony-vegas-pro/553-sony-vegas-zen-tips-3-preview-lag

Regards
Derek

I did watch the tutorial on preview screen lag (after searching all I could think of with the words "audio" and "sync"). I did not connect the lag with audio. I tried what was suggested on the tutorial for generic lag. Changing from "best-full" to "good-auto" fixed clip #2 but the first clip in which I had made chroma key changes stayed the same. I then changed the preview window to "draft-auto" and viola! all was in sync again.
This is the first software I have used with an effective chroma key embedded. I have formerly used Ultra 2 which is no long available for updated editing software. This issue highlights to me the intensity of the background workout the computer is doing in order to chroma key and read/write the background simultaneously.

Please know that once a video has been rendered, there will be no video lag in the final video.
It is only something that may happen during editing.