MediaPlayer error -2147483648 when playing file on internal storage

I'm using the Audio Capture sample on android.com to record and play back audio on actual devices. (Motorola touch pad, and Samsung Galaxy S).

When I define the audio file path as

mFile = Environment.getExternalStorageDirectory().getAbsolutePath();

record and playback works.

But if I set the audio file as

mFile = getFilesDir().getAbsolutePath();

OR

mFile = getDir("media", Context.MODE_PRIVATE).getAbsolutePath();

OR

mFile = getDir("media", Context.MODE_WORLD_READABLE).getAbsolutePath();

record seems to work, but playback fails with

ERROR/MediaPlayer(4559): error (1, -2147483648)

What function will return the correct internal storage directory to save audio files for playback only within my app?

The code in question is in my onCreate function. (In the example, they have it in the Constructor, but I moved it to onCreate because otherwise getFilesDir() and getDir() have no context to work.)

public void onCreate(Bundle icicle) {
    super.onCreate(icicle);

//  mFile = Environment.getExternalStorageDirectory().getAbsolutePath();     // OK
//  mFile = getFilesDir().getAbsolutePath();                                 // BAD
//  mFile = getDir("media", Context.MODE_PRIVATE).getAbsolutePath();         // BAD
    mFile = getDir("media", Context.MODE_WORLD_READABLE).getAbsolutePath();  // BAD
    mFile += "/audiorecordtest.3gp";
    Log.e(LOG_TAG,mFile);
//  ...
}

When I record to external storage (and playback works properly), the log looks like this:

06-17 10:07:3