To embed YouTube Tumblr you first have to copy the embed from a Youtube video, access the HTML source code for your Tumblr Blog and paste the code in the body section. Follow the step by step instructions below.

Copy embed code from Youtube video

1. Go to the video you want to embed onto Tumblr.
2. Click on the 'Share' button.
3. Click on the 'Embed' button.
4. Copy the code snippet that appears.
   

Embed video automatically

1. Log into Tumblr
2. Click on the 'Video' icon.
   
3. Next you can insert the embed code into the 'Embed a Video' tab field, or upload a video using the 'Upload a Video' tab options.
4. Enter in a caption for your video and click the 'Create post' button.

Embed Youtube Video Tumblr

1. Log into your Tumblr account.
2. Click on the 'Text' link icon to create a post.
3. Click on the 'Post' field.
4. Click the 'HTML' icon from the menu.
   
5. Paste the Youtube embed code into the window.
6. Click the 'Update' button.