DJI Inspire 1: Transcoding/correcting "log" footage

• Report rights infringement
• published: 06 Feb 2015
• views: 20064

On February 5th, DJI posted a new tool entitled "Inspire 1 Transcoding Tool v0.91": http://download.dji-innovations.com/downloads/inspire_1/DJI_Transcoding_Tool_v0.9.1.zip This app does two things: 1) It transcodes the video files from the H.264 codec written to the SD card to the Apple ProRes codec. 2) It corrects video captured in "log" color mode by restoring the contrast and saturation that are missing from log-mode video. My initial thoughts: 1) Why transcode from a low-bit-rate, highly-compressed codec (H.264) to a high-bit-rate, moderately-compressed codec (ProRes)? It can't improve the quality of the video; it can only increase the file size, and it may degrade the video quality in the process. 2) Why a separate app to correct the log-mode footage? Why not just restore the missing contrast and saturation with the tools in your video editing software? I decided to run a test. On my first Inspire flight, I recorded a 6-minute and 45-second 4K video. A portion of this video is presented here in four ways: 1) Unmodified; you can see the washed-out quality of the log-mode footage. This file is about 60 megabits/second. 2) Transcoded and corrected with the DJI app using the "proxy" setting, which resulted in a 7.4 GB file (more than 2.4 times the original size). This file was about 140 megabits/second. 3) Transcoded and corrected with the DJI app using the "LT" setting, which resulted in a 25.3 GB file (more than 12 times the original size). This file was about 475 megabits/second. 4) The original (non-transcoded) H.264 file with contrast and saturation adjustments made with the Fast Color Corrector effect in Adobe Premiere Pro CC 2014. These four versions are presented in two ways: first in a round-robin fashion, then again in a split-screen fashion. My conclusions: 1) Apple ProRes files range from enormous to unbelievably enormous. This makes sense when I am recording the 4K output of my Sony A7s video camera on my Atomos Shogun. But it makes no sense whatsoever when the source material is highly compressed at such a low bit rate. 2) There is no discernable difference between the "proxy" and "LT" transcodes, despite the enormous difference in file size (7.4 GB vs. 25.3 GB). Again, transcoding cannot improve the quality of the video; it can only degrade it, and take up more space in the process. 3) It took me about 45 seconds to make four adjustments to the Fast Color Corrector effect. The result is very close to the correction done by the DJI app. (* Details on these adjustments below) I see the value in an external tool that corrects the log-mode footage for people who don't have access to decent video-editing software. It would be just as valuable as the GoPro Studio software that corrects ProTune footage from those cameras. So why does this tool export to the Apple ProRes codec, with its enormous file sizes? That certainly can't be helpful to less-advanced users who don't have decent video editing software. Here is what I hope DJI does: 1) Increase the bit rate of the H.264 files that the Inspire writes to its SD card. The video I am getting is very very very compressed, and I would really appreciate a higher bit-rate. 2) Provide log-mode correction presets for the big video editors (Premiere Pro, Final Cut Pro, etc.). * Here are the adjustments I made to the original footage in Premiere Pro CC 2014. I applied the "Fast Color Correction" effect, and then: 1) Changed the "Input Black Level" to 30.22 2) Changed the "Input Gray Level" to 0.89 3) Changed the "Input White Level" to 248.11 4) Changed the "Saturation" to 120 That's it. It's not exactly the same as the DJI transcode app, but it's very close.