Kinoma Notes

We recently had a cus­tomer who wanted to choose the “best” frame rate for his encoded content.

To that end, his goal was to crank up the frame rate as high as pos­si­ble. He used Kinoma Player’s Per­for­mance Test fea­ture on one of his videos and con­cluded that the best frame rate for encod­ing for his Treo was 18 FPS (frames per second).

Unfor­tu­nately, there are a cou­ple of incor­rect assump­tions in there:

• That the result of a Per­for­mance Test on one piece of con­tent is applic­a­ble to other content
• That when it comes to FPS, “more is better”

Using the Per­for­mance Test feature

The Per­for­mance Test fea­ture gives you the aver­age max­i­mum frame rate pos­si­ble with the cur­rent video. What it doesn’t do is tell you what would be the “best” frame rate for the cur­rent video.

Even though this video has an aver­age max­i­mum frame rate of 54.1 FPS, it needed to be encoded at 15 FPS in order for the most challenging-to-decode parts to play smoothly on a range of devices.

Also, this fea­ture isn’t meant as a pre­dic­tor for how another video will per­form. Sim­i­lar types of video encoded using the same encod­ing para­me­ters should show com­pa­ra­ble results, though.

Choos­ing a frame rate

Here’s the secret: For smooth video, always use a frame rate that’s a sub-multiple of the source frame rate. In other words, choose a frame rate that divides evenly into the frame rate of your source.

Why? Imag­ine 30 keys on a piano, rep­re­sent­ing one sec­ond of source video. A frame rate of 18 FPS is like try­ing to play 18 of those keys if they were spread out across the same space. At first, your fin­ger will line up with the first key — so far, so good. But then your fin­ger will hit a com­bi­na­tion of the 1st and 2nd key, then a com­bi­na­tion of the 3rd and fourth keys, etc. It would sound pretty hor­ri­ble, and the equiv­a­lent in the video world is stuttering.

For 30 FPS video — NTSC video is tech­ni­cally 29.97 FPS, but it’s gen­er­ally accept­able to round it up when encod­ing — good choices include 30, 15 and 7.5 FPS. 15 FPS is a great start­ing point.

A frame rate of 7.5 FPS seems a bit crazy, doesn’t it? But a frame rate of 7.5 FPS doesn’t mean that half-frames are being encoded. Since 30 divided by 7.5 is 3, it sim­ply means that every third frame is being encoded.

And know­ing is half the battle

Now that you know how to choose frame rates, be sure to check out the Kinoma Forum if you have any addi­tional ques­tions about encod­ing con­tent for Kinoma Player.

This entry was posted on Tuesday, September 25th, 2007 at 12:00 am and is filed under General, Kinoma Producer. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.