Video Compression

VideoNerd

Is it correct to double the bandwidth when the frame rate of video stream is switched to 60Hz from 30Hz?

Common sense says: if you double the number of frames then the bitrate should be also doubled.

On the other hand, the temporal distance between frames in 60Hz is twice less than those of 30Hz. Moreover, for camera captured video the motion blur is also reduced at 60Hz and as a result the temporal redundancy tends to be better exploited.

i conducted the following test:

1) i took 60Hz video gaming content (significant motion, fast zooms). i deliberately took graphics content to exclude motion blur issues.

2) i converted 60Hz video to 30Hz one by removal each second frame.

3) i applied x264 with constant QP mode (in order to exclude Rate Control impact): QP = 20, GOP =30 frames, no B frames (IP-only GOP structure).

Results:  Bits per pixel (bpp) for 30Hz video is 0.331 while for 60Hz it’s 0.291 (better coding efficiency).

Conclusion: migration to 60Hz from 30Hz video does not require doubling of bitrates. Although, in case of I-only coding the bitrate should be doubled (because temporal prediction is disabled).

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