This piece is called 'The Perilous Night' performed on a prepared piano 1944, this is something that a lot of people won't have heard of, as it is targeted to the art market more than entertainment, but Cage still managed to sustain a long career out of his works, working right up until his later life. Another aspect of an Avant Garde career route is that the product tends to be the direct vision of the artist at work, unlike an X - Factor winner who sings other songs or even an Indie band who can take the rough idea from another artist to help produce thier image, for example here is a song called 'The Fire' by Ben Howard.
This sounds similar to the song 'Go Down Easy' by John Martyn, in terms of dynamics and lyrical themes, with other elements taken in form artists such as Erik Mongrain, who uses a distinct percussive and finger tapping guitar technique, as seen in the next example, 'Airtap'
In terms of credibility for Avant Garde artists, it is usually determined by how much influence they have on others based as well as based on their creativity.