Working Directory: null Environment: null

You need to make sure that the /data/data/com.example.foo/files/ffmpeg file has the correct file permissions.

You can check file permission with the following command :

String[] command = new String[]{"/system/bin/ls", "-l",
                                "/data/data/com.example.foo/files/ffmpeg" };
Process process = Runtime.getRuntime().exec(command);
BufferedReader reader = new BufferedReader(
                    new InputStreamReader(process.getInputStream()));
int read;

String output = "";

String line;
while ((line = reader.readLine()) != null) {
    output.concat(line + "\n");
    Log.w("myApp", "[[output]]:" + line);
}  
reader.close();
process.waitFor(); 

The output would be something like this (depending on actual permissions , in this case the permissions are 777) :

[[output]]:-rwxrwxrwx u0_a67   u0_a67     254460 2015-03-02 17:12 ffmpeg

You can set the permissions to 744 , with the command below :

String[] command = new String[]{"/system/bin/chmod", "744",
                                "/data/data/com.example.foo/files/ffmpeg" };

If you are executing this command from outside activity (from a service lets say) , your permission will have to be 777 (not 744)

Maybe you need to add this permission to your AndroidManifest.xml file:

android.permission.WRITE_EXTERNAL_STORAGE