I recently made a video of a trebuchet, with a PocketLab in the weight basket. I had the PocketLab set to record the three-axis accelerometer at maximum sampling rate. I recorded a test firing using the iPhone PocketLab app on an iPhone 6.
My apologies for the video quality; this was an early test and I didn't worry about lighting or anything. However, you can clearly see that the bump in acceleration is not synced to the trebuchet's motion, and the data stops before the video. Also, the graph does not extend all the way across the screen.
It looked correct (synced, and with the data across the screen) while I was recording it. The problem was only visible when I saved it to the iPhone (which I later exported to YouTube).
Let me know if you need me to test this under other conditions.