First the difficult, complicated and limited successful method. This requires the experience of knowing what sites are generally successful to download from. In general, low security sites offer less encrypting protection on the videos. These videos are easier to download but compromise the security of your pc. Lower security settings on any anti-spyware or browser settings may make this easier. Do so on your own risk. Find a video you want.
Use Google Chrome browser for best results. Click in the settings icon in the right top corner. Click more tools, then developer tools. Make sure the volume is on. Make sure the video plays. When the new tab comes up click the network tab. Then click all or media. You will be directed to hit f5 to reload the page. You will be able to hear if the video automatically loads. Or if you need to manually press play again. Okay, now you are looking for the longest bar in the timeline. A solid bar is best. Check the type to see that it says video mp4, media or something similar. Now right click the bar and choose copy link address. Now paste this into the address bar and click enter if you didn't choose paste and go. You should have the video playing with a black screen background. Once the video is playing and it must be kept playing. Right click and choose Save as. Choose a desirable location. Then you can rename the file. Press save. And your video will download. You will then have this streaming video to watch permanently without buffering!
The drawbacks to this first method are numerous, even if you have the patience and experience. Firstly, this works on a limited amount of websites and videos. Important sites such as youtube it will not work for. These videos are layered in multiple video streams and encrypted. However, you can download almost any video with the correct software. Some new videos that have high encryption you may have to wait to a time when you are able to properly download the video. However this works on youtube and most sites. Many of these free download software bundles your computer with adware. This isn't worth it in the least. Some of these software may have a worthless upgrade. There is one reliable software I have found. No adware and it downloads almost any video. Well worth the price tag.
Method two is to buy and use Wondershare video converter. I do not make any money from recommending them. This service has simply worked for me. You can even record videos that won't download by doing a screen shot capture and letting the video run. This is pretty good if you can figure out how to set the timer. You must let the video run at a time when you have fast internet. And limit the sound as much as possible as the recorder will capture any noises from your real physical environment.
I hope this guide helped to let you download your favorite videos online for free. (Free once you buy the software if you used method 2) You no longer have to deal with buffering.