A UPC is very similar to an ISRC. Whereas an ISRC is a virtually embeded code, a UPC is a physical bar code used for the whole album/collection of songs. UPCs are found on anything for sale, in shops, supermarkets etc.
How do artists make money on YouTube? For starters, by putting music on YouTube for free with a digital music distributor.
YouTube address the most common questions asked about the recommendation system, such as how they personalize recommendations.