![]() H.264 encoders divide each video frame into horizontal and vertical rows of tiles called macroblocks. P-frame Comparison 1080p30 (IP 15-frame GOP): I-frame Comparison 1080p30 (IP 15-frame GOP): P-frame Comparison 1080p24 (IBP 12-frame GOP):ī-frame Comparison 1080p24 (IBP 12-frame GOP): I-frame Comparison 1080p24 (IPB 12-frame GOP): I then displayed and cropped them at 200% magnification in side-by-side 24Mbps versus 54Mpbs comparison shots, and saved screenshots of each comparison. After loading the video files into a 32-bit Adobe After Effects project, I selected I, P, and B-frames from the second GOP in each video sample. In 1080p30 mode, the D5100 records in an IP format using a 15-frame GOP. In 1080p24 mode, the D5100 records in H.264 IPB format using 12-frame GOP. This type of subject presents a myriad of high-contrast moving images that tax the motion tracking and bitrate allocation algorithms of the camera's H.264 video encoder. I selected a sunlit scene of a running stream of water with highlights on the water ripples. The camera was locked down on a tripod and used the Neutral Picture Profile. I took these shots with a Tamron 24-70mm f2.8 lens set at 70mm, f5.6, and ISO 100. I recently shot comparison tests of the D5100 in 1080pp30 video modes, using the stock 24Mbps bitrate, and hacked 36Mbps and 54Mbps bitrates. D5100 macroblock artifact comparison:stock 24Mbps versus hacked 54Mbps ![]()
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