Variable not passing between functions

Don't use same variable in your function

Try,

function audioPlayer($nT)
{
    echo ' ... all html ...';
    $numTrax = $nT;
    return $numTrax;
}

you need to define the variable in function like

global $numTrax;

to use the global variable. Otherwise, it will create a new variable with local scope.

If I don't guess wrong, I think you are using wrongly the keyword global.

The assign $numTrax = $numTrax; in

function audioPlayer($numTrax)
{
    $numTrax = $numTrax;
    return $numTrax;
}

is actually assigning the value of the local variable $numTrax to itself.

You have to define the global var just as:

$numTrax = null ;

and in your function you you must avoid shadowing the global one renaming the parameter, and declare the global variable (so no new local variable is created), like for example:

function audioPlayer($paramNumTrax)
{
    global $numTrax; // declare it exist a global var somewhere called $numTrax

    $numTrax = $paramNumTrax; // Asign the local value to the global variable
    return $paramNumTrax;
}

More info: http://php.net/manual/en/language.variables.scope.php

(in some cases could happen that: "Using global keyword outside a function is not an error. It can be used if the file is included from inside a function.". Don't know if this is your case)

Hope this helps.

Change your function to this:

function audioPlayer($newNumTrax)
{
    global $numTrax;

    echo ' ... all html ...';

    $numTrax = $newNumTrax;
}

To access or reassign a global variable within a function you need to use the global keyword to bring it into scope. The function's argument should have a different name from the global variable so as not to get them confused. Then, just assign the value of the argument variable to the global variable.

Going by how you've called it, this function doesn't need to return anything. It just sets the value of the global variable.

For the audioPlaylist call, there's no reason to pass $numTrax as an argument. It's a global variable, so all functions can access it. Define the function like this:

function audioPlaylist($user_id, $username)
{
    global $numTrax;     #now you can use the global variable in this function

    #rest of function here
}

... and call it like this:

audioPlaylist($user_id, $username);

Please note that using global probably isn't a very good strategy for designing your program. I recommend passing variables to functions rather than relying on globals. If your functions get too unwieldy, break them into smaller functions.

Variables aren't global by default in PHP. You have to declare them as such in every function where you want to use them, or set $GLOBALS['numTrax'] instead.

With that said, though, it's generally considered a really bad idea to rely on global variables, for several reasons. Most involve "action at a distance", or relying on implementation details that are now ten times harder to change rather than coding to an interface. (The general prohibition is a bit overly broad, but globals aren't needed in 95%^* of the cases where they're used.)

^*(Totally made up number, cause i don't have stats on it with me. But know that it's too high. :P)