Wal-Mart Stores Inc. is ending its digital music sales this month after seeing increased competition.The world's largest retailer confirmed Tuesday that it will stop selling MP3s as of Aug. 29. Customers who already bought digital music through its site may continue to use and manage their music there.Wal-Mart began selling digital music in 2003 to compete with Apple's iTunes, which has become the largest seller of digital music. The company also faces tough competition from Amazon.com.The company said it will now concentrate its digital efforts on its Vudu.com video-streaming service, which it acquired last year.NPD industry analyst Marshall Cohen said the dynamic of retail is changing, and sometimes companies are better off focusing on what they do best rather than offering something that doesn't deliver an above-average experience for consumers."It is very easy to become antiquated very quickly in the entertainment industry," he said. "If you are losing ground, and they probably were losing ground more rapidly year after year, it's probably better to regroup and retool."