I uploaded couple of short Xvid video segments from two different DV files to YouTube.

I then played them in default, "Watch In High Quality", and &fmt=18 mode. After each pass I used VideoCacheView to retrieve the resulting files. In each case VCV shows two files in the cache:

Default - VideoCacheView shows one with a name scheme like flaXX.tmp with a .tmp ext and another with a scheme like get_video[X] and a long string of characters as the extension. When copied to a folder elsewhere, the string of characters on the get_video version gets changed to an .flv extension. The .tmp version gets changed to an .flv extension.

They seem to be the identical file - video bitrate is around 327kbps audio is 64 kbps mono

Watch In High Quality - again one with a .tmp extension and another with a video[x].flv name scheme.

When copied, they retain the same name, both with .flv extensions and again appear to be exact duplicates. They have higher bitrates on audio and video than the default files. These test files show 713 and 801 kbps video and 96 kbps audio, still in mono. I get the same numbers using MediaInfo and simply hovering the cursor over the files.

&fmt=18 - Again, a .tmp file and now one with the video[x] naming scheme but an .mp4 extension. However, when copied, the .tmp file is assigned an .flv extension, the video[x] file is assigned an .mp4 extension, but they still have identical properties - right at 500 kbps video (one shows 500, the other 501), both show 121 kbps 44.1 stereo audio.


Does this mean that for each video YouTube creates three versions?

I see the video bitrate is actually significantly lower on the &fmt=18 version than on the WIHQ version - right at 500kbps -vs- in this case 713 - 801 on the WIHQ. It's clearly more than a simple tradeoff in bitrate, with &fmt=18 you get stereo and gain 25 kbps on the audio but lose 200 - 300 kbps on the video.

Sub-question 1) How is it an .flv and .mp4 file have the exact same properties, seem to be the same file? I thought they were two different file types. Apparently there's something I don't understand about file naming conventions.

Sub-question 2) Why do 2 versions of each file show up - the .tmp and the other one? Under VideoCacheView the .tmp file shows as being under "Temporary Folder" and the other as under "Web Browser". Which one is the system playing when I'm watching on YouTube?

Thanks for all input