Can't start Screen Sharing, Video Chat, or Audio Chat

Question

Hi there,
I've been through countless Apple Discussion and other website threads, but I can't figure this out.
I just got my dad a brand-new iMac with Mountain Lion 10.8.3 on it. I'm using a MacBook Pro, also with 10.8.3 on it. We're both using the Messages app, signed into our respective Google Talk accounts (not Apple IDs with Google email addresses).
But for the both of us, "Invite to Video Chat," "Invite to Audio Chat," and "Share Screen With..." are grayed out in the Buddies menu, even though both of us have "Video Chat Enabled," "Audio Chat Enabled," and "Screen Sharing Enabled" checked off. I unchecked the option to consolidate the various Buddy Lists in the Messages > Preferences > General pane, and when I go to my Gmail account's Buddy List, I see the four buttons underneath the list (with my dad's name highlighted), but only the "A" button is clickable--not the other buttons for Audio (the phone icon), Video (the camera icon), or Screen Sharing (the two rectangles layered over one another icon).
Does anyone have any ideas on how to remedy this (short of using a completely different method of screen sharing)?

Answer 1

HI,
On your GoogleMail Page pull down your own Name/ID
Click Account
Choose "Products" from Menu.
Enable "Talk" (Sign in to Dashboard far right)
This is separate from the settings to actions on the Web Mail Page accessed in the Settings icon.
However I am not sure if the setting absent there if TALK has not been enabled as it was done some time ago for for me as well.
Jabber apps can have  Priority Setting to allow people to be logged in via several devices and be sure a messages goes to the right device at the time.
iChat version 3 through 5 had the same Priority as the Web Browser login and would stop text Messages getting through.
iChat would show the Buddy still on line if they were logged in via the web page at a later stage
but the Video and Audio green icons would disappear from the Buddy List and the icons at the bottom would be greyed out.
Messages has a default priority of 0 compared to iChat's 23.
However I have never managed to work out which end of the scale outranks the other.
Essentially logging in to Google Mail web page to Check things is likely to stop the ability to Video chat.
This is because Jabber app use a Protocol  called Jingle to connect and this is not compatible with the SIP iChat and Messages uses.
It is included in the Web Browser Plug-in you can get from Google.
The default setting for the Bandwidth setting is the NONE one.
However it can pay to set it to 500kbps.
This helps when  internet speeds that are faster vary too much for the Buffering in iChat and Messages to work.
In broad terms a 5% variance in a 10Mbps download speed can be 500kbps.
Forcing Message to only use 500kbps is fast enough for 4 way video chats but is well below any variance interference.
It can also help where the ISP slows the connection as it thinks it is a Peer-to-Peer file sharing event.
Video and Audio chats (including Screen Sharing) are peer-to-Peer connections.
7:33 PM      Saturday; May 18, 2013
  iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.3)
 G4/1GhzDual MDD (Leopard 10.5.8)
 MacBookPro 2Gb (Snow Leopard 10.6.8)
 Mac OS X (10.6.8),
 Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images."  No, Seriously