Quality-Based VBR Descrepencies

I am using H.264 Intel QuickSync hardware encoding for a 34m 4k video. Settings are below

image image

Video has three filters
-Brightness 110
-Contrast 55
-Hue\Lightness\Saturation 100\100\130%
-First 8 Seconds has a green screen animated text overlay on a second video track

For some reason the resultant video has is super-grainy even though it has 124Mbps data rate. Note that quality I am using quality-based VBR set at 80%. Original video from DJI Osmo Pocket has 100Mbps data rate.

Exported Clip Info:
Video: MPEG4 Video (H264) 3840x2160 29.97fps 124400kbps [V: h264 high L5.1, yuv420p, 3840x2160, 124400 kb/s]
Audio: AAC 48000Hz stereo 382kbps [A: SoundHandler (aac lc, 48000 Hz, stereo, 382 kb/s)]

Previously two days before I encoded an Intro with all of the same settings except the quality % is set to 60%. This video seems much better-looking with a higher 37MBps data rate.

Video: MPEG4 Video (H264) 3840x2160 29.97fps 36980kbps [V: h264 high L5.1, yuv420p, 3840x2160, 36980 kb/s]
Audio: AAC 48000Hz stereo 382kbps [A: SoundHandler (aac lc, 48000 Hz, stereo, 382 kb/s)]

What am I doing wrong here? Is is exporting based on proxy files rather than the original Osmo Pocket clips or something else that I missed?

Shotcut always exports from the originals.

Any chance that encode was done with libx264 rather than Quick Sync? If so, then these differences seem about right.

Would the words blocky or smeary also apply? Grain alone is not a typical artefact of compression algorithms, so something else could be going on.

How much motion is in this video? If there is a lot, then 124Mbps for Quick Sync may be insufficient. For older generation Core processors, Quick Sync can produce files up to three times larger than libx264 to reach the same visual quality.

Yes its blocky and smeary. I happen to have a backup of the mlt project file and I am in process of re-editing and then will re-encode to see if there is some corruption in the project. There should be an autosave of projects files with a parameter to save to a selectable number of project copies such as last 10.

Both files are encoded using H.264qsv. That is the specific reason I downloaded Shotcut to get the hardware encoding support. Th first video is 1m20seconds long, encoded in 5 mins and produced an mp4 with 36Mbps data rate and a file size of 933MB. The second file is 35m long, encoded in 4 hours and produced an mp4 with 124Mbps data rate and a file size of 30GB but for some reason this second encode has terrible quality. Its as if its not even using hardware encoder and the quality is terrible.

Ok Solved!

Looks like the project was somehow corrupt. The backup of the original project that I made manually and exported overnight is back to decent quality. This H.264 qsv 60% VBR video comes out looking good an with a 15.6GB file size looks waaaay better than the H.264 qsv 80% VBR video I kept trying to generate over the past couple of days.

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