First in Safari go to the Develop menu and select "Start Debugging JavaScript" from the drop down.
Next you'll want to add a call to debugger in your javaScript like this.

 
function onSomeThing() {
  debugger;
}
 

You will then be able to run your page and have the Safari JavaScript debugger add a break point where your debugger call is placed.

Charles Proxy provides easy access to FLV file information such as video codec and embeded metadata.
To find this information you will want to find and select the flv in Charles. When selected you will then want to select the "Response" tab in the opposite window to revel flv file info.