Hi,
Whilst LexSchellings is right that there can be Bandwidth (yor portion of your Internet Connection) issues there are some things to check and possible tweak.
If your can get Video but not Audio then the fault could be at thier end rather than yours.
First.
They should check the Video menu and see that the option for the Audio (Microphone) is Enabled (The wording changes in some versions)
2nd
They should then go to the iChat Menu > Preferences > Video pane and check the green Response bar is moving when they talk.
3rd
The Microphone selected in the drop down on the same Video pane should also match the choice in System Preference > Sound > Input tab
3a)
The volume setting in here should be high enough to get the blue response bar to at least 1/2 way, preferably 3/4s but without banging into the right hand end.
Summary so far.
They should check the Mic is On in the Video menu
That the Mic matches in iChat and the System Preferences.
That they can see the blue bar in System Preferences > Sound s and the green bar in the video pane of the iChat Preferences move when the speak.
Next.
During a chat open the Connection Doctor.
This will tell you the Local and the Buddy's Bit rate and Frame rate as well as the two green bars.
The Bit rate needs to be over 128kbps
The frame rate needs to be 15fps or higher. (lower than 10 and the video gets jerky)
The bit rate will fluctuate but should not vary that much.
In iChat > Preferences > Video Chat > Bandwidth Limit you can directly and sometime adversely effect the Video with this setting.
It should ideally run with the setting at NONE.
However some ISP internet service vary so much that this is not practical.
Do not use it at less than the 200kbps setting. 500kbps may be "best".
In the days when many people's internet connection was 256kbps download and 128kbps upload the ichat Buffering would cope with fluctuation in the connection speed.
It would do this by dropping an odd video frame or two.
There comes a point though when the Audio cannot not be synced when this happens and iChat will drop the audio.
A 5% variance in a 128kbps upload will drop the feed to below 100kbps by the time the connection to the ISP overheads are taken in to account.
However a 5% fluctuation on a 10Mbps service will be more than some people actually get for a connection.
This is why dropping ichat to 500kbps can smooth out the connection so that fluctuations are less critical.
It can also help if one end is so much faster than the other end.
In some cases where a Fast Buddy "Calls" a slower one iChat can seem to "think" the buddy is not responding.
Summary of this
Using the Connection Doctor balance the Connection speeds with the Bandwidth Limit.
Do not use the lowest setting as it is actually below the min needed for Video chats (1-1)
500kbps should smooth out most internet fluctuations and still be high enough for 4 way Video chats
Setting the Bandwidth Limit can also help if the two of you are on vastly different speeds.
You can change the Bandwidth Limit during a Live chat.
The Connection Doctor will not "jump" to the new speed but will get there gradually as the Buffering smoooths out the change.
Next (or really at the same time)
The Buddy needs to be possibly doing this at their end as well.
Change the setting on one computer and only proceed at the other when the Connection Doctor shows the new speed.
Finally.
If they have a Headset (Mic and Headphones) then it may be crucial about how these are set up in iChat and System Preferences.
Open System Preferences > Sound > Input as well as the iChat > Preference > Video Section.
In both places change the sound input choice to anything but the headset.
Now in System Preferences Set the Mic here "First"
Then set it in iChat (2nd)
Repeat for System Preferences > Sound > Output and the output choice in iChat.
It has been seen that blue tooth headsets in particular need the System Preferences > Sound > Input set up before any app is set up to use the Mic.
It seems that some USB mics also need this.
9:21 PM Wednesday; March 20, 2013
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Mac OS X (10.6.8),
Couple of iPhones and an iPad
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