Step 1) Check the site http://scmplayer.net/;
Step 2) Choose the what player you want;
Step 3) Press Edit Playlist;
Step 4) On the Song Title box, you put the name, and the Song URL box, you put the link of the music on youtube;
Step 5) Press Configure Settings and make all what you want there;
Step 6) Press Done on the right corner of the screen;
Step 7) Copy the code; go to Tumblr >> Customize >> Custom HTML and paste the code below the <body>, to find where are the <body> use Ctrl+F;
NOTE: The player will not appear at the Customization page, to see how the player looks, save and go to your Tumblr page.
Step 8) Comment here if it's works.
This post was suggested by the reader @nlavelli