The rumors are true -- developments in video are exploding into the world of email marketing. It feels like we've been waiting for ages to use video (and deliver it safely into inboxes), and the time is finally here!Video usage is expanding right now primarily due to three major factors: 1) people are spending more time watching videos online and are thus more receptive to video in email; 2) the expenses involved in creating and hosting video are falling; and 3) video is consistently showing that it increases engagement and relevance. According to Mike Madaio, Chief Internet Architect at QVC, people who watch video tend to convert better. Assuming that this continues to be the case, we can count on seeing more and more video playing in our inboxes throughout the months (and years?!) to come. Trends in video usage With video rapidly becoming more prevalent and with capabilities constantly improving, it's too early to assert "rules" or all-encompassing best practices. For example, while videos have most often occupied the secondary messaging spot, we're seeing more cases of videos as the primary calls-to-action, such as in this Shop NBC video series. In addition, while the ideal length for videos highlighted in emails is generally thought to be 30 to 45 seconds, the main call-to-action in this Apple email links to a 30-minute video. Short and sweet still rules the email world, but Apple reminds us that the rules can be broken, and we're sure to see all kinds of variations as brands experiment with video. The benefits and limitations of three primary methods of video delivery: Static image. A static image simply features a still of one of the frames of the video, using strong visual cues (such as the ubiquitous sideways-triangle "play" symbol) to encourage subscribers to click through to Web-hosted video. This is the simplest, least expensive and most common method of including video in email. However, this method lacks eye-catching movement and requires the subscriber to click for video and audio. Smith-Harmon client REI uses this method in some of its emails, as does Thrillist (this is a hosted screenshot, so the link won't work here, but you get the idea). Embedded video gif. A video gif uses a compressed, streamed animated gif to deliver video-quality content. Liveclicker, a new video startup, is currently enabling this approach. Many brands, including Overstock.com and Sears , have been using this technique, and it's an awesome way to allow subscribers to preview longer video and to see motion straight from their inboxes. Audio can't be enabled from within the email using this method, however, as email messages projecting sound might be an unwelcome surprise for many recipients, especially in the workplace. Embedded video. Actual embedded email (that's not blocked by ESPs) is the next step. Currently, Goodmail Systems is rolling out its CertifiedVideo service, which enables both audio and video. Using this method, the video and audio will start playing right when subscribers open their emails. This could increase engagement, but it could also increase irritation; there are bound to be some brands that take video and audio too far. High-quality, engaging videos could draw subscribers in and give them a reason to look forward to certain marketing emails, but if subscribers deem a brand's emails "annoying" or worry about the disruption of audio, they may be pushed to unsubscribe or decrease their open rates. To dive deeper into methods of video delivery, check out Eli Ashery's great post from last month. Watch for more on this topic next time. We'll give you the scoop on types of email content that make sense in video and show how top brands are leveraging video in cool ways.