to find out what audio codec a video is using you will have to use third-party software, I recommend Media player classic home cinema which you can download from here or here.
Using Media Player Classic
Open the video file you want, then right click anywhere on the video then choose properties
Then you will see the audio codec (AAC) as in the below image
Using PotPlayer
You can download PotPlayer From here or here or here.
Open the video file you want, then right click anywhere on the video then choose playback/system info
Then you will see the audio codec (AAC) the video is using as in the below image
Using VLC
You can download VLC from here or here.
Open the video file you want, then right click anywhere on the video then hover over tools then select codec information
Then you will see the audio codec (AAC) the video is using as in the below image
