I found your useful plugin and I thank you for it. However I didn't work for me so I tried to figure it out and found that the link address Speakerdeck provides is https, not http. So I tried to fix your code a bit to use a regular expression rather than the simple wildcard format as below:
wp_oembed_add_provider( '#http(s)?://speakerdeck.com/u/.*/p/.*#i', 'http://speakerdeck.com/oembed.json', true );
I hope someone find this useful.