Radamés Ajna

Misc experiments with JS/WebGL/Typography

Experiments

Video Experiments

Might be good to mention the size difference, e.g. via

(await FileAttachment("flor-default@1.webm").blob()).size/1024/1024

Also, is webp seekable and would be an alternative if direct frame access is required?

Fabian Iwand

yes, the size is a good point, however in my example they have almost the same size ?  I guess because of the increased number of I-frames. webp should be smaller in size. I'm not sure about youre other question, I think webp is seekable, what do you mean by direct frame acess?

> however in my example they have almost the same size ?

Oops, you're right! I was going by the info in the network tab and accidentally compared the wrong files. Should have double checked.

I guess that renders my question regarding webp moot. I was assuming (without doing research) that animated webp might have better optimization for individual frames, at a better quality/size ratio. However, afaik there's no HTML/JS API for webp to jump to jump to a specific offset in the animation?

Sorry, apparently I'm a bit dense and out of my depth: The ffmpeg documentation states that the default for -g is "12", which means that "-g 30" would increase the group size.

Did you use "-g 30" for the "Fast Seeking" video or for "Defaults"? If it's the former, I don't quite understand why increasing the group size would enable faster seeking.

Sorry for the noise. https://developers.google.com/media/vp9/bitrate-modes states that the default is 240, which answers my question.

yes that's right, the default and recommended is 10*the frame rate, it makes sense for compression and streaming, no one is interested in larger files and fast seeking. However, this is the secrete sauce of interactive projects such as https://www.nytimes.com/interactive/2020/09/09/world/middleeast/beirut-explosion.html and https://www.nytimes.com/interactive/2020/11/21/science/artificial-intelligence-fake-people-faces.html

Decreasing the group of pictures increase the number of I-frames, which are the full image frames, and we need that for fast seeking, otherwise, it needs to be calculated from b-frames and p-frames, which slows things down.

Yup, I got confused because I initially thought that the default number of i frames / GOPs was higher. :)

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