[AltruisticGapHN]

Hey thanks I didn't know about this tool.

Interestingly since I have the older download from ~3 weeks ago I just ran mediainfo on it, and the new download from today. Then I just switch tabs in terminal so I can easily see what changes.

Old / New

    vp09 / vp09 

    filesize   488 mb   / 391 mb

    OVerall bitrate   3274 kb/s   /  2620 kb/s

    Bits/(Pixel\*Frame)    0.036 / 0.028

I don't see anything else significant.

It seems to me in recent weeks YouTube has changed the streams, added new "high bitrate Premium" streams (edit: WHILE lowering the bitrate on the older existing streams like 137!), and perhaps the one I downloaded earlier, despite being a larger filesize, was not encoded correctly?

The new file despite being 20% smaller (~400 mb instead of 500), has the smoother color banding, and doesn't show the ugly jittery grainy artifacts.

I used to think larger filesize is better but I guess Iḿ going to get the Vp9 from now on...

[ubercow13]

I have noticed that Youtube often re-encodes videos, replacing the data for a certain stream type/number with a new encode.

[AltruisticGapHN]

Yes that is probably what it was!

I'll remember that even two+ days after the initial upload, there may still be reencoding. I thought this was only few hours after the creator uploads.

So the smaller filesize also is not necessarily a sign of lower quality. In this case it's because it gets a quick first encoding like zip with fast compression, and then it gets reencoded presumably by something much more CPU intensive.

That said from 500mb to 400mb is a bit dodgy but what do I know maybe VP9 is that good.

[bavell]

Interesting! Thanks for running mediainfo on them to compare.

When encoding videos there's a "speed" parameter that basically tells the encoder to spend more CPU time compressing the frames. It results in a smaller output size while maintaining the same level of quality but takes much longer to encode. I'm sure that's part of what YT is doing here, an initial quick encode to get the video live then another pass to reduce filesize for long term storage. Good find!

I'm guessing that the perceived higher quality in the smaller file is because the encoder was able to find a more accurate way to represent those frames with the same or fewer number of bits since it has more time to search for the optimal encoding.