How To make video file size reduced by 50% without losing Quality ?

It's a broad question... It all depends on your requirement what your intended use is? Another part of this is which plateform are you using I.e: Mac or windows for editing? I mean, if your going to process between packages some may try to keep the quality 'lossless' then use the H.264 at given Total Bit/rate Or VBR2 for Final Output. H.264 is really a standard in the online publishing right now set by Apple. HOWEVER, as the4K market is on the rise so has the Compressor quality and much more have been updated too. Read up on H.265 that's the one people should be aware I would suggest. I hope that helped. Feel free to question or comment on my website.

Personally I would reduce the frame rate (frames per second) of the video. This will automatically reduce the file size. While most high quality videos have a high frame rate,  its not always necessary to keep the rate that high. It is not always a good idea to convert files including video to formats that have better compression, because we cannot assume that the end user has the required codecs to view the video. To avoid compatibility issues, I would change as little as necessary and that  means sticking to the provided file format and not convert so as to avoid future problems.

I think unnecessary frames should be remove

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There are many ways to do this task, and scholars still work on it. If you want some more advance way, you can read about wavelet comparison. and for more simple and traditional one:

- the vid is a list of pics.

- get the diff of the next images from the current image.

- instead of listing all full images, do the effect on the first and so.

be careful, if the first is damaged.. the full vid is as well ;)

There are many ways to achieve that but I will tell you a simple one. You just need to convert your video file type to MKV which reduces the file size by a lot without loosing and significant video quality.

Large video files are slow to upload and download. One of the most popular tools that can significantly shrink the file size without losing quality is Handbrake. It is popular due to three reasons:

• It can convert video from nearly any format, e.g. .wmv – Windows Media Video File, .avi – Audio Video Interleave File, .m4v, .mov, etc.
• It is free and Open Source
• It works on Windows, Mac and Linux

This tutorial illustrates how to compress a video file for the web on a Windows machine. The sample file I used to compress was called WL-Video.wmv and its original size was39.0 MB. After compression the file size was down to4.40 MB. The compressed video format is MP4 as it is the most supported video format on the web. Depending on your original video file, following the instructions in the tutorial, the file size may still be reduced if your video file is already MP4 format.