ffmpeg – Stereo V4L2 Synchronization

How do I synchronously record from 2 cameras? While I am able to acquire two v4l2 streams, one camera is always delayed by ~1 second. Tried many options such as vsync, itsoffset and so forth.

Current code:

ffmpeg -y 
-f v4l2 -input_format h264 -video_size 1080x1080 -framerate 20 -thread_queue_size 32k -itsoffset 0 -i /dev/video0 
-f v4l2 -input_format h264 -video_size 1080x1080 -framerate 20 -thread_queue_size 32k -itsoffset 0 -i /dev/video1 
-filter_complex "(0:v)(1:v)framepack=sbs" 
-f mp4 
-c:v libx264 
-b:v 2M 
-preset ultrafast 
-pix_fmt yuv420p 

In short, the second V4L2 camera stream (/dev/video1) always starts approximately ~1 second AFTER the camera first V4L2 stream (/dev/video0). The second V4L2 stream needs to be “pushed” ahead by ~1 second before it is merged with the first via the framepack filter. (so it is synchronized with the first stream)

Is there a way to “wait” until both V4L2 camera devices are “ready” before the recording process begins? Or, perhaps adding ~1 second to the 2nd stream prior to filtering?