It is safe to say that nowadays nearly every single project here at firstborn contains Flash Video files (short: flv). Due to our success and experience, I think it is also safe to say that we are well-versed with web video and Flash Video in particular. Sadly, it is as well safe to say, that with each single project that we work on, we encounter new problems with that video format, even if it is simply the dark magic one has to perform, to achieve good filesize-to-quality ratios or a simple action like looping the video fluently without a millisecond of lag between the ending and recurring beginning.

Many of our former projects contain PNG image sequences, just so they can be looped smoothly, and therefore make our designers happy (read: make them stop getting on the developer's nerves). The downside of this technique is the much heavier filesize compared to an flv solution. This problem has been solved as of today. Imagine our surprise when we practically "stumbled" upon the solution of some major difficulties. The secret is the "keyframe interval" option when compressing the Flash Video. Usually you would try to set this to a slightly higher value, because this means smaller filesizes. In our case, the optimal (and embarrassingly obvious) solution would be to make it as small as possible though: "1 keyframe per frame"... This way the flv loops perfectly smooth and when embedded it in a MovieClip-Timeline in Flash, can - with the help of a little bit of code - finally be treated like a "real" regular MovieClip. I annouce the discovery of the holy grail: As long as they don't have sound, we can now change the playback speed of flvs and reverse (!!!) them. How cool is that.

I made 4 little demos, to illustrate what I'm talking about. Have a look at the different performances, as well as the filesizes:

http://www.jensfischer.us/demos/flvPlayback01
keyframe every 1 frame - video filesize with same settings 2,830 kb

http://www.jensfischer.us/demos/flvPlayback02
keyframe every 3 frames - video filesize with same settings 1,708 kb

http://www.jensfischer.us/demos/flvPlayback03
keyframe every 10 frame - video filesize with same settings 1,103 kb

http://www.jensfischer.us/demos/flvPlayback04
automatic keyframe setting - video filesize with same settings 900 kb



2 Responses to “The holy grail of flash video”

  1. jan:
    August 20th, 2008 at 1:24 pm

    ey ey ey, du machst mir irgendwie angst. du alter haxxX0r :-)

  2. John:
    April 21st, 2010 at 1:59 pm

    Awesome find! It always frustrated me that I could never play embedded flvs in reverse on the timeline smoothly.

    Though I am not finding this technique to save must in the way of file size. Turning the keyframe interval or “Key Frame Distance” as it’s now called in Adobe Media Encoder to 1 sends the file size of the flv through the roof. In some cases the exported flv was 4x larger than one with the Key Frame Distance set to the default (which I believe is 30)

    Any new findings since this post that have helped manage this problem?

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