Video preprocessing

The raw videos captured by a camera are in general distorted, rotated, flipped, etc. Preprocessing is hence often needed to make them human readable.

Remap raw videos

The arena-remap application remaps an input raw video (-i) typically obtained from a camera. arena-remap can rotate and/or flip and/or undistort an input video. The resulting video is displayed and/or saved to an output file (-o).

To undistort the video, arena-remap requires camera intrinsic (lens) parameters.

Example: Remaps a video in live using the camera parameters related to the North camera (defined in the arena package):

arena-remap -i input/raw_north_front.mov

Example: Advanced example:

Step 1: Calibrate the intrinsic parameters:

arena-calibrator -i input/raw_north_front.mov \
    -r 90 -d horizontal \
    -j ~/.arena/camera/arena/remap_north_front.json

Here, arena-calibrator applies:

• a clockwise rotation of 90° (-r);

• an horizontal flip (-d).

Step 2: Remap the video:

arena-remap -i input/raw_north_front.mov \
    -r 90 -d horizontal \
    --camera ~/.arena/camera/arena/raw_north_front.json \
    -j ~/.arena/camera/arena/remap_north_front.json \
    -o remap/remap_north_front.mp4

Here, arena-remap applies:

• a clockwise rotation of 90° (-r);

• an horizontal flip (-d);

• a distortion based on the intrinsic parameters (--camera) obtained at step 1 (note that the extrinsic parameters are ignored).

Finally, arena-remap saves the remapped video (-o) as well as the corresponding camera parameters (-j).

Step 3 Calibrate extrinsic parameters using arena-calibrator:

arena-calibrator -i remap/remap_north_front.mp4 \
    --camera ~/.arena/camera/arena/remap_north_front.json \
    -j ~/.arena/camera/arena/remap_north_front.json \
    --scene arena

Flattening a 360° video

The arena-nfov application flattens 360° videos as those involved in the U23 project.

arena-nfov -i U23/360-stadium-3_2023-06-11_out_20230611_142510.mp4