Pocketcine's blog

Most of the principles governing compression of video data for playback on constrained devices like the mobile phone apply also to the audio track. This article focuses on audio data compression. This is not an article about audio level compression, a method for altering the volume levels of audio.

Just like video compression, there are two forms of audio compression, lossless and lossy. In the first case audio is compressed without loss of information. An example is the FLAC (Free Lossless Audio Codec). In the second case information is lost. Examples are Vorbis, MP3 and AAC. We'll discuss codecs later.

In a recent test, we compared how well four different projects compared in terms of their compressed data rates. It did not surprise us that a 3D animated short compressed to the smallest file relative to its running length. Nor did it surprise us that video shot on a high end consumer camera produced the largest file relative to its running length.

Think Small
Shooting video for a mobile video has special challenges because of the wide diversity of delivery platforms, from cell phones with 2 inch screens to iPhones and other portable media with much larger screens and higher video resolutions. If you want your mobile viral video to travel far and wide, then you need to think small and short. A typical mobile video resolution is 176x144, with file sizes ranging from 100kb to 1 megabyte. iPod resolution, 320x240, is becoming more common.

The focus of the Pocketcine project has been short videos that can be downloaded quickly and inexpensively over the air to cell phones.

The smaller the file size, the fewer bytes would flow over the air, triggering smaller carrier charges. Impatient mobile consumers will not be left tapping their toes, waiting for big video files to land on the storage media of their cell phones before playing. One of the main reasons why the world’s most successful viral mobile video, The Crazy Frog, is so widely distributed is that it is only about half a megabyte in size.

From the beginning my research told me that 3D animated shorts would compress most efficiently and live action video the least efficiently. Flash generated vector art and traditional hand-drawn animation would fall into the middle of the spectrum. In an upcoming blog, I’ll publish a primer on MPEG-4 compression so that you will understand the reasons why. However some of the main reasons are that a 3D animation does not have the sharp edges that compression algorithms don’t compress well, it has smoother and less random gradations, its color space works well with the compression algorithms, and the artist has more control over backgrounds and movement than possible with live action video.

You would think that mobile video would not need to be proselytized. After all there is a daily flood of news releases about mobile video arriving in mailboxes.

However, what I have discovered is that digital artists are only peripherally aware of the medium. They know it’s coming, sometime in the future. But they are just too busy to study it from the point of view of production. Plus there is a dearth of information about creating and deploying mobile video on cell phones. I imagine it was like telephones when they first came along. People knew how to talk to each other, but they had to learn how use the new technology created to make a new form of talking possible.