Its operation process is so simple, you just need copy and paste the URL of the YouTube videos which you want to download and convert to it, and then select output format, here I choose MP4 for my iPhone, afterwards, specify where to save the output files, and click “OK” to start. You see, all are done, isn’t it easy?

HD Video Converter can easily convert HD video formats such as AVCHD (mts, m2ts), H.264/AVC, MKV, MPEG-2 (ts), DivX, HD WMV, MPEG-4 and Quick Time.

Of course, if you have higher expectation of the output files, you can click “Custom” to adjust video and audio parameters like codec, aspect ratio, bit rate, frame rate, etc. on the following panel:
Since I am a Windows user, I do not know many about Mac, and I just know some of my friends are using Safari to download YouTube videos on their Mac OS. One day by chance, when chatting with one of my friends, he told me that he also used Pavtube

Pavtube iPhone video converter, can convert AVI, MPEG, WMV, MOV, etc to Apple iPod video.

(YouTube Converter for Mac) to download and convert YouTube videos to MP4 for his iPod and iPhone.
This utility joins multiple .MTS files into a single .m2ts file on the hard drive of your PC, and then you can work this file with Sony Vegas smoothly.
Secondly, I’d like to say something more about the older version of Sony Vegas. Although the robust Vegas Pro 9 has been released not long ago, and it boasts supporting AVCHD definitely, I know some users are not willing to spend much more money to upgrade their old version to the newest one. Many people are still using Vegas 7 or former version to edit their video files.
To these people, the only way to let Vegas work with MTS files is convert these files to Vegas compatible formats like WMV and MP4 previously. The converter I personally used is Pavtube MTS/M2TS Converter, I usually use it to convert my MTS files for my iPhone, and its output formats is various, you can select one for your Vegas. To be honest, I’ve tried many other converters before choosing it, this one can make my audio and video go in the same way, so it finally won my appreciation. Hopefully it will also do you a favor.
As for other AVCHD camcorders, because no research has no right to speak, I can say nearly nothing about them. I’m not sure whether they have certain plug-ins or utilities like Sony’s HDD Handycam Utility, or something else to help them import MTS files to Vegas. If not, may use Pavtube MTS/M2TS Converter to do previous conversion work still be an available way?

Provides five ways to rip Blu-ray DVD to PC, AVI, DVD, ISO, iPod, MP4, WMV, MPEG, DivX, etc.

Of course, if you have the latest version of Vegas or have your better way to solve this problem, just let my words go, or you can share your ideas to me as well. Thanks Prior.