Apple’s HTTP Adaptive Protocol

In June of 2009, Apple introduced a new video format that provides adaptive bitrate over http.  If those words don’t sound like they should go together – or in that order – don’t worry. It’s actually not as complex as it sounds and is a really cool technology.

Adaptive bitrate allows the quality of the video to adjust depending on your internet connection speed. The faster the connection, the better quality the video will be. While it has been executed in a number of ways on the desktop, this is the first implementation for mobile devices. Additionally, the implementation uses a standard http connection – a very basic building block of the internet. This protocol is very easy to scale and requires no additional software.

While the adaptive bitrate does have advantages, there are three specific disadvantages for publishers:

  1. It requires quite a bit of transcoding, as you need to transcode a minimum of 5 times per episode. If you chose to do separate profiles for iPad and iPhone, there are 12 or more transcodes required.
  2. The only tool Apple provided for transcoding is a command line tool for OSX.
  3. The spec is quite unfriendly to advertising!

Castfire utilizes a custom transcoding engine and queue that distributes the work across many different processors and servers. We are able to quickly divide the workload across available machines to process as quickly as possible. The queue enables each client and output profile to maintain a different priority to ensure that the most important episodes and profiles are completed as quickly as possible. Since Castfire acts as the origin server for your CDN, there is no need to be transferring all of the files between servers or to your desktop – it is completely automated.

Rather than tinker with the encoder from Apple, we built our own encoder for our LAMP infrastructure. We have now transcoded over 1600 hours of http adaptive video — almost 2 years worth — using our custom encoding solution. We are extremely happy with the quality and the performance of it.

Lastly, we have utilized our existing infrastructure, that enables ad insertion from any VAST enabled ad server, to allow publishers to monetize ads in the http adaptive format. Clients like CBS Mobile and the Washington Redskins are using this today to monetize videos across all of the iOS devices.

If you would like to view the http adaptive profiles from some Castfire customers, check out: