any best hosting service for my video blog ?
You’re going to have to give us a bit more than just “a video blog”. What software are you running, how many visitors do you get, how many concurrent users, etc. Without that information all we do is guess …
For video you are better off hosting the videos on youtube and linking to the videos through your website. Any cheap shared host will run this setup.
If you are going to host the website videos yourself go for dedicated hosting.
For video blogs or “vlogs”, I always suggest a strong VPS since you will be streaming the content which is a lot more accessible which drains more resources.
I would go vps like grandma says, check out some vps offers on this forum, i have my vps at jaguarpc.com 2 months free baby!!!
Upload your videos to Youtube / Vimeo etc and then link to them / embed them on your blog is probably a better solution than trying to upload them and host them on your own server - let someone else pay for the video bandwidth 
For video hosting you will require FFMPEG web hosting provider.
No you don’t, unless you specifically need to convert uploaded videos on the server. For just hosting video files, it’s not required.
best way is to upload your videos on youtube and then link it to your blog … you can upload it on youtube, vimeo, metacafe.
Go with dedicated vps server, it would be good for video streaming and also it will support your software too. Youtube is not sufficient for your task because there some limitation and no one need it at least when you going to upload a long duration videos a hug amount of videos.
so go with vps server