What's a free and simple way to add watermarks to a video?

Hi,

I take sports videos with my Sony XR500V camcorder which produces 1920x1080 .m2ts files. I usually join them together and that's enough. I use Sony Playmemories (the s/w that comes with the camcorder), and it does the job easily for this task.

Now I need to do some editing (e.g. a title slide with some text) as well as a semi-transparent watermark (logo and/or text). I already have Sony Vegas, but adding a watermark has not been easily, and I must be doing something wrong with the bitrate, etc. because the enjoined video is degraded resolution, etc.

Is there a simple s/w package out there that will work with a .m2ts file, allow me to easily add a watermark and create a new file that is same quality of resolution? Free/cheap would be great as well.

Thanks for any help out there.