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I have some videos I recorded with my cell phone that I want to crop using Avisynth's crop(). I am using x264vfw with VirtualDub which asks for a target bitrate. I usually just get the bitrate from the vid's properties in Windows Explorer and plug that value in for the target bitrate for the new encoded video, but, since I am cropping it, I don't want to use the full bitrate. Ideally, I would be able to find out the bitrate of only the region I am wishing to crop. After all, if the original video is 1920x1080 with a total bitrate of 30 mbps (30,000 kbps) and I want to crop it down to a 1080x1080 region, I don't want to use the bitrate of the full, uncropped video.

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You can only estimate the bitrate as proportion of your crop. If you have 30,000 Kbps for 1920*1080 pixel, then for 1080*1080 pixel this would mean 16,875 Kbps. If there is more complexity inside the crop region than outside, I would even increase the target bitrate further.

However, if your videos are not that long and not intended for streaming I wouldn't invest too much thought into saving some disk space. The video quality will degrade anyway with the encoding process and a high bitrate will help you avoiding too much loss.

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  • That's what I was afraid of. It's not easy being a pedant trying to find the absolute perfect bitrate to yield the best quality/disk space ratio. I'll probably just use original bitrate in the new video for good measure, though using the proportional calculation would probably be just as good. – oscilatingcretin Sep 20 '15 at 0:12

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