What format should I use for my Video Podcast?

What some producers do when it comes to video is they create an "HD" version and put it on YouTube and embed it on their website for website visitors.

Then they create a smaller version (I believe quick time lets your export in a format for portable devices) and upload that to your media host. The smaller file is cheaper to host, faster to download, and doesn't take up as much room on your audience's phone.

So when someone comes to your site, they see the YouTube version, when they subscribe to your show they get the smaller version for smaller screens.

MP4 (MPEG-4)

MP4 is currently the most widely supported video format playable by most portable audio players, Internet-connected TVs, and software-based media players.

MP4 is a video format based on Apple’s QuickTime video format and is essentially identical to the Apple QuickTime MOV format, with additional features. 

MP4 video format most commonly contains AAC encoded audio and H.264 encoded video.

M4V (Apple’s iTunes implementation of MP4)

M4V is a non-standard file extension of the MP4 (MPEG-4) format (see above) popularized by Apple’s iPod, iPhone and the iTunes Store.

M4V is essentially identical to the MP4 except it has additional capabilities added by Apple. Since the file extension of .m4v was popularized by iTunes, the media opens in the iTunes application rather than by the default media player. The consumer of the media will typically be presented a “Save As” dialog if the iTunes application is not installed on the computer. The M4V format also allows for the inclusion of Apple’s FairPlay Digital Rights Management (DRM).

Note: Even though the .m4v and .mp4 file extensions are essentially interchangeable, we do not recommend it.

Source: blubrry.com