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Comment by WhitneyLand | Hacker News Reader

"The H.264 video, 300 frames long is 175KB. A single frame of that video in PNG is 1015KB. It looks like we're storing 300 times the amount of data in the video. But the file size is a fifth. So H.264 would seem to be 1500x as efficient as PNG. How is this even possible? All right, what's the trick?"

Mostly the trick is they're comparing lossy to lossless compression which doesn't even make any sense.

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Yes, as they explain shortly after, in the next section "shedding weight".

They're not actually confused here. It's a writing style, where you pose an interesting problem/scenario, then explain it.

I don’t think they are confused either just don’t think it’s a good way to introduce the point.

When good expositors choose motivating questions, say like 3 blue 1 brown, they don’t usually make apples to oranges comparisons. The best examples motivate while making sense before and after you learn.

Sorry, but it's only apple to oranges if you already know the answer. That answer, explained in the next section, is very clearly intended for someone who didn't already know it:

> This concept of throwing away bits you don't need to save space is called lossy compression. H.264 is a lossy codec - it throws away less important bits and only keeps the important bits.

> PNG is a lossless codec. It means that nothing is thrown away. Bit for bit, the original source image can be recovered from a PNG encoded image.

Actually I had the same thought, but this is obviously an article for people who don't know the difference between lossless and lossy compression. Ok, you might argue that it's not a good fit for HN, but going by the many times it seems to have been posted here, some people disagree.

It makes tons of sense to compare those numbers. It's a big part of how you benchmark lossy compression. I guess in some sense they should use BMP instead of PNG but it's arguable.

Sure that’s true. But if something makes sense for a technical benchmark that’s not a guarantee it’s the best way to introduce a concept. I just think other approaches could have been more clear for this case.

Discussed elsewhere here: h.264 supports lossless storing.

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