I have tried downloading video lectures but I couldn't.please help me out with that......Thanks

 

If you are talking about the video on this forum then you can do as this way:

1. Open the video file you want to watch - Video Lectures.

2. Waiting for about free seconds when the video start to play and then press the stop key.

3. Moving the mouse cursor to the range of video.

4. Press the right button of mouse and choose Save as (choosing the directory of HDD you like) test.ogv.

5. Waiting for the video file to download completed.

6. Go to the directory of HDD to select the video file test.ogv.

7. Setup the test.ogv file association which web browser you wish to watch.
(You can use your own way to do, if you don't know the method then you can using google to search).

8. Go to press the test.ogv file.
(You just waiting to watch the browser to showing the video, you can enlarge the video from the corner of right bottom.)

Good luck.