How to add audio track in video output

[nikunjprajapati77]

Hello Sir,
please help me how to add extra audio track in video output and also let me know to speed up video by 2x

thanks,
Nikunj Prajapati

My Code
$encoding_job = $zencoder->jobs->create(
array(
"input" => $input,
"audio_tracks" => array(
"merge_with_existing" => "true",
"masters" => array(
array("url" => "http://learning-services-media.brightcove.com/audio/celtic_lullaby.m4a")
),
),
"outputs" => array(
array(
"label" => "web",
"speed" => 5,
'url' => $output,
'watermarks' => array(
array(
'url' => $image,
'text' => 'Logo',
'x' => '05',
'y' => '-12%',
),
array(
'url' => $PNGfileName,
'text' => 'Score',
'x' => '05',
'y' => '2%',
),
)
)
)
)
);