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Scene change detection during encoding and key frame extraction code

In a previous post we explained how to generate thumbnails for each scene change using Edit Decision Lists from your non-linear editor of choice. Sometimes, though, you won't have an EDL along with your video assets (for instance, when you are using off-airs or videos edited by somebody else). In those situations we can still create a thumbnail for each scene change thanks to how frames are structured in digital compression.

According to Wikipedia, a GOP structure specifies the order in which intra- and inter-frames are arranged. A Group Of Pictures can contain the following frame types:

EDL to HTML with thumbnails for every shot change

For video production companies video asset management is an important part of our post-production workflow. Being able to re-use footage can reduce our production costs considerably and enhance the creative editing process. The more footage we have, the better the video will look.

As our best footage always ends up one way or another in a sequence, it made sense to us to use Edit Decisions Lists as the starting point of our online video asset management.

The problem is that EDLs are text-based and, therefore, don't give a visual representation of the shots. For this reason, we needed to convert the information in an EDL, the timecodes, into thumbnails that would correspond to every shot change of the original sequence. We also wanted to use these thumbnails to control a low-res video file so we could preview not just a frame but the whole length of a clip.

For this purpose, we designed the following EDL to HTML workflow using Powershell, FFmpeg and the JW Player. We hope you'll find it useful.

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