Combine your music to create a new song.

After using the extension feature in /v2/submit, a new part2 song will be generated, and using the concat endpoint,you can link the part1 and part2 songs together, so that the task will have an integrated song.If you extend it several times, that is, if you have parts 1, 2, 3, and 4, using the concat endpoint will link parts 1, 2, 3, and 4 into a song;