AVC is lossy (excluding some lossless profiles aimed for professional/broadcast use). This means that you can compress the source at even higher bitrates (50 Mbps for example) but you will still have differences/loss compared to the source. You can at max expect a 'visually transparent' result, which means that during playback you can't detect differences between two sources. CRF have almost the same encoding engine as a 2pass. If you want to target some specific bitrate/filesize, it's better to use the 2pass encode rather than do various different CRF.
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