If your webcam doesn't work (it's not detected) with the new Google Plus Hangouts or with Google Talk Video, here's a possible way to get it working.
Before proceeding, make sure Google Talk plugin is installed.
Both Google Plus Hangouts and Google Chat Video use the Google Talk Plugin for which we'll apply a 'fix' similar to an old Skype work-around (preloading v4l1compat.so):
Ubuntu 32bit:
sudo apt-get install libv4l-0
sudo mv /opt/google/talkplugin/GoogleTalkPlugin /opt/google/talkplugin/GoogleTalkPlugin.real
echo '#!/bin/sh' | sudo tee /opt/google/talkplugin/GoogleTalkPlugin
echo "LD_PRELOAD=/usr/lib/libv4l/v4l1compat.so /opt/google/talkplugin/GoogleTalkPlugin.real" | sudo tee -a /opt/google/talkplugin/GoogleTalkPlugin
sudo chmod +x /opt/google/talkplugin/GoogleTalkPlugin
Ubuntu 64bit:
sudo apt-get install lib32v4l-0
sudo mv /opt/google/talkplugin/GoogleTalkPlugin /opt/google/talkplugin/GoogleTalkPlugin.real
echo '#!/bin/sh' | sudo tee /opt/google/talkplugin/GoogleTalkPlugin
echo "LD_PRELOAD=/usr/lib32/libv4l/v4l1compat.so /opt/google/talkplugin/GoogleTalkPlugin.real" | sudo tee -a /opt/google/talkplugin/GoogleTalkPlugin
sudo chmod +x /opt/google/talkplugin/GoogleTalkPlugin
And then restart your browser.
Please note that you may need to repeat the process if you upgrade to a newer Google Talk Plugin version.
The instructions above were tested on Ubuntu but should work on other Linux distributions too (though the v4l1compat.so file location may be different).
Revert the changes
To revert the changes, run the commands below:
sudo rm /opt/google/talkplugin/GoogleTalkPlugin
sudo mv /opt/google/talkplugin/GoogleTalkPlugin.real /opt/google/talkplugin/GoogleTalkPlugin
[via AskUbuntu]