If you take a look at the video link it contains a part "&range=<number>-<number>". Remove this part of the link and it will download the entire video.
The following url will download a 1.69 MB chunk of the video.... from byte range 7127040 to 8908799.
8908799 bytes - 7127040 bytes = 1781759 bytes = 1.69 MB
Remove the part in red and the entire video will be downloaded.
Code:
http://o-o.preferred.ams03s07.v21.lscache1.c.youtube.com/videoplayback?signature=29CDE8B43AC7963F4B52B3F791FDA07E6C288E29.5A024EF4B75CDFBEE34B8DEEB16F2178A960CCCD&range=7127040-8908799&key=yt1&algorithm=throttle-factor&mt=1341498618&source=youtube&sparams=algorithm%2Cburst%2Ccp%2Cfactor%2Cid%2Cip%2Cipbits%2Citag%2Csource%2Cupn%2Cexpire&ip=94.0.0.0&upn=1qAnkJm55qc&ipbits=8&factor=1.25&itag=34&expire=1341521655&sver=3&burst=40&cm2=0&ms=au&cp=U0hTRlVNT19KT0NOM19NR1NHOnlwTHZLLXRRWnMz&fexp=906717%2C912301%2C913002%2C907217%2C907335%2C921602%2C919306%2C922600%2C919316%2C920704%2C924500%2C924700%2C913542%2C919324%2C920706%2C907344%2C912706%2C902518&keepalive=yes&id=49b5013249504955