FOMS: Funny Name, Serious Talk about HTML5, Bitrate Switching, WebM, and WebSRT

Oct 8, 2010


Update: JW7 is now available. Check it out here.

Last week, in the midst of our normal support requests and software development, we found a way to squeeze in a little extra time to attend the Open Video Conference and associated meetings here in New York. Everyone here at LongTail is a strong believer in open media formats, but it is rare to see so many people who are as committed to it as we are – assembled in one place.

For most of us, the most exciting part of this whole week was the Foundations of Open Media Software Workshop, organized by Silvia Pheiffer, a member of and frequent contributor to the HTML5 media specification.

Bitrate Switching

Going into the workshop, we were especially interested in hearing everyone’s thoughts on adaptive bitrate switching. While this is one of the most popular features of our Flash player, HTML5 doesn’t offer any mechanism for handling this, so we can’t offer this functionality in our HTML5 player. Thankfully, the workshop included a brilliant mix of browser vendors (Philip Jägenstedt from Opera, Chris Blizzard from Mozilla), Codec designers (John Luther of WebM and Christopher “Monty” Montgomery, Gregory Maxwell,Timothy Terriberry, and Ralph Giles of Ogg Theora and Vorbis), and player developers (Steve Heffernan of VideoJS, Michael Dale of Kaltura).

Several viable alternatives were presented for bitrate switching, however, there are several technical challenges to contend with. First, there is a question as to whether to use several long files and simply switch between them using range requests, or to break the files up into thousands of short (~5 second) “chunks”, and play them back sequentially. Ultimately, using several long files presents a big challenge, both in terms of time to start playback and live streaming. All current file formats would require that the index of switch points be loaded for all files before starting the video. This dramatically increases the amount of time required to begin playing back a video and makes live streaming impossible, since the index could not be dynamic. Additionally, while a new file format could be designed to handle this, it would be difficult to achieve widespread adoption.

This meant that a mechanism that used several manifest files and many small files seemed quite attractive. The browsers would simply load the manifest for the appropriate quality, and then load a different manifest if necessary. Furthermore, the browser could periodically check for additional entries in the manifest, effectively allowing for a livestream with DVR. The browser vendors noted that this could be very simple: they will need to implement a mechanism for synchronizing media playback over multiple files for accessibility (alternate audio tracks) regardless, so why not use this to simply stitch together video files, one after another? Finally, this mechanism closely mimics Apple’s bitrate switching mechanism, so it has a proven track record, and the tools built to support it.

Unfortunately, the format discussion was so involved, it left little time to discuss how the browsers would choose to switch streams. A loose JS API was proposed for this, with the possibility that browsers would build in their own default logic. However, based on this feedback from the group, we will draft a specification for this, post it for feedback, and include it in the JW Player as soon as possible.


One of the other highlights was the community’s interest in WebM. Much of the video on the web today relies on the H.264 for encoding video. Unfortunately, H.264 cannot always be used without paying royalties to a licensing organization, MPEG LA. While the HTML5 video spec was being developed, Ogg Theora was the only realistic open source alternative to H.264. Unfortunately, it’s performance is not nearly as good as H.264. WebM is a project that was started up by Google after their acquisition of ON2, which offers a high-performance, royalty-free codec for video. For this reason, the participants were especially interested in the possibility of adopting it as the baseline codec for HTML5. In fact, our HTML5 player already supports it, as both Opera and Chrome have this functionality built into their production browser, and Firefox has it available in their new beta. The biggest concern was that Apple and Microsoft have both refused to include support, and while Adobe recently announced VP8 support, there have been no dates set.


Finally, there was a discussion over web accessibility, specifically subtitles and closed-captions. This is near and dear to our heart, as JW recognized the importance of this early on, and made sure to include accessibility functionality ever since. The new standard for subtitling and captioning on the web will likely be WebSRT, and we’ll be working closely with the drafters of that specification and browser vendors to include support as soon as possible.

As intellectually stimulating (and fun) as these workshops are, it’s important to us that we’re a part of these discussions so that we can continue to develop the most innovative products, and that those products are standards based. So keep your eyes peeled – we’ll be working hard to integrate these technologies into all of our products as the standards develop.