You can upload and playback 3D videos as either rectangular 3D videos, VR180, or 360 3D (VR videos).
YouTube supports left-right (LR) side-by-side stereo layout for 3D videos. The video should contain stereo metadata as:
- st3d box in .mov/.mp4,
- StereoMode element set to side-by-side LR in .mkv/.webm, or
- FPA metadata in H264 SEI headers
If your 3D video doesn't have 3D metadata, you can add it using preferred video editing software, like Sony Vegas Pro or GoPro Studio. You can also use the FFmpeg tool.
H.264 encoded video in .mov or .mp4 container
ffmpeg -i input_file.mkv -vcodec libx264 -x264opts "frame-packing=3" output_file.mp4
Matroska and WebM video
ffmpeg -i input_file.mkv -c copy -metadata:s:v:0 stereo_mode=1 output_file.mkv
Note: After uploading a video with the tags, it will only play back as 3D after it's been fully processed. Before then, it will play side by side (in other words, not in 3D).