feature: Add preview from gphoto

[andi34]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "x" next to an item)

• New feature

What changes did you make? (Give an overview)

Changes adapted from couz74@4b5ba4c for latest Photobooth source, adjustments added to not conflict with other preview mode options.
Closes #83

• install dependencies sudo apt install ffmpeg v4l2loopback-dkms -y
• create the virtual webcam modprobe v4l2loopback exclusive_caps=1 card_label="GPhoto2 Webcam"
  • /dev/video0 is used by default, you can use v42l-ctl --list-devices to check which /dev/* is the correct one
• Give permissions to /dev/video* sudo gpasswd -a www-data video
• reboot once
• In the admin panel set preview mode to from gphoto

Troubleshooting

• For Installation Problems on v4l2loopback-dkms Just see the issue here

• Issue with Chromium (did not test firefox), if there is another webcam like
  bcm2835-isp in my side it take it by default instead of the Gphoto one... therefore I always do rmmod bcm2835-isp

• Chromium sometimes doesn't detect the Gphoto webcam if it wasn't loaded first with a Gphoto Webcam having the Ffmjpg feed. To do that I send the command in a shell sudo gphoto2 --stdout --capture-movie | ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video0 then I start Chromium and check if a testing webcam website work ( https://www.aaronbenjamin.design/camera-app/part-2/ or https://www.onlinemictest.com/webcam-test/ for example)

Conversation on andreknieriem#242:

For it to work on startup I had to edit /etc/rc.local:
modprobe v4l2loopback exclusive_caps=1 card_label="GPhoto2 Webcam"
rmmod bcm2835-isp

rmmod bcm2835-isp was needed as chromium was taking this device instead of the V4l2 one.

How it work
We use v4l2loopback to create a virtual device and gphoto2 --stdout --capture-movie | ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video0 to send the photo preview to it.
On "take pic" button we start the process and end to before the picture is taken to free gphoto2.

It is a ugly draft, I hope I will improve it and post the update here.

There is still two issue:

• Sometime I need to run sudo gphoto2 --stdout --capture-movie | ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video0 first and load chrome a first time with a webpage asking for the camera. If I don't do so sometime chrome doesn't detect the V4l2 camera launch from php.
• On the takeVideo.php I need to use a sleep() method in order to allow the stream to launch, still need to figure a way to have something cleaner

Hi,
In the admin panel the setting "See preview by device cam" must indeed be set.
Then there are three things:

• modprobe v4l2loopback exclusive_caps=1 card_label="GPhoto2 Webcam" create the virtual webcam and sudo gphoto2 --stdout --capture-movie | ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video0 in the takeVideo.php send the outpout of the Gphoto command to the /dev/video0 device (you can use v42l-ctl --list-devices to check which /dev/* is the correct one).
• The second thing is the issue with Chromium (did not test firefox), if there is another webcam like
  bcm2835-isp in my side it take it by default instead of the Gphoto one... therefore I always do rmmod bcm2835-isp.
• Finaly Chromium sometimes also doesn't detect the Gphoto webcam if it wasn't loaded first with a Gphoto Webcam having the Ffmjpg feed . To do that I send the command in a shell sudo gphoto2 --stdout --capture-movie | ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video0 then I start Chromium and check if a testing webcam website work.

As you can see there is still some issue with the solution XD

Is there anything you'd like reviewers to focus on?