You can try to use freeware VLC player to record from webcam on your mac:

1. Launch VLC
2. Go to "File"->"Open capture device"
3. Refresh both lists. Select audio/video devices you wanna record from. Configure them if necessary.
4. Check the "Stream/save" checkbox and click the "Settings..." button.
5. Check the "File" checkbox and choose the filename and location of your recorded file.
6. Select encapsulation like MPEG TS.
7. Choose a video codec like mp2v and its settings
8. Choose an audio codec like mpga and its settings
9. Click the "OK" button
10. When you're ready to record, hit the "OK" button in the "Open..." dialog.
11. You can stop recording by hitting the "Stop" button