Comparison of video types available on YouTube: HQ18, HQ22, HQ35, HQ37, FLV, MP4, HQ, HD, etc.

Update (12-Jul-10): YouTube has recently added support for 4096*3072 ("ultra-high") resolution videos, as reported here.

I frequently download videos from YouTube, using Mozilla Firefox and Video DownloadHelper extension. However, DownloadHelper shows that many YouTube videos have multiple versions available, labeled as HQ18, HQ22, HQ35, HQ37, etc. There does not seem to be any official explanation of these different versions.

So today I set out to

1. Understand the difference between these video types
2. Identify the version with the highest quality

I started with this video (Check out E3 Spotlight) (screenshot below), as it was available in all versions that I've seen on YouTube so far.

Click image to view in full size

The findings are below

++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Schema Details
[Video Type]: [Container]; [File Size]; [Ratio]; [Relative Quality]
++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1. Basic / Normal: FLV; 718 KB; 1x; Low
2. HQ18: MP4; 1.4 MB; 2x; Medium
3. HQ22: MP4; 4.5 MB; 6.4x; Very high
   
4. HQ35: FLV; 2.7 MB; 3.9x; High
5. HQ37: Container?; Size?; Factor?; Super
   

What it shows: HQ22 (and now HQ37 - an even higher-quality video) has the highest quality on YT, if file-size is used as an indicator of video-quality. Additionally, for HQxy, a higher value of xy doesn’t necessarily mean an increase in video-quality over a lower xy value.

Verification of the above findings: The above findings have been found to hold true for all 5 of the following videos (except for HQ37 - which is known to have higher-quality than HQ22, but this has not been verified yet)

1. Windows Gaming at E3
   
2. Gaming for Everyone
   
3. Introducing Google Squared
   
4. Google Health - Product Overview
5. Nokia Booklet 3G first video
   

Result of My Memory Test