Intel QSV slowing down during encode

[dickh]

I sometimes use the Intel QSV codec for making low-compression h264 copies of .ts files to improve compatibility with my editing software. On typical SD material and my old i5 3450 system I would get ~ 350fps conversion speed. Having now upgraded to an i5 8600 I was initially very pleased to see figures of ~750fps, however as the conversion proceeds (say a 1hr film) the rate gradually reduces to ~ 200fps so that the overall average is no faster than before.
My first assumption was that this was a thermal problem however the CPU temperature on the Gigabyte system monitor hardly breaks 50deg C with just the QSV codec running and even with 100% CPU load in addition, it only touches 55deg. Also, if I queue up two files in succession, the second file also starts at 750fps and drops off in the same way. The Task Manager performance window shows the GPU usage dropping at the same rate as the fps.


HandBrake version 1.07 64bit


OS is Windows 10 Home 64 bit V.1709 with 8Gb ram. )



Activity Log: https://www.dropbox.com/s/hmdrzc06i21exet/log.txt?dl=0

[Woodstock]

Are you letting Windows do power management, which tends to lower the priority of non-interactive tasks?

[dickh]

I had the windows power management set to 'balanced' although I have just switched to 'High Performance' and edited the Intel Graphics setting to 'Maximum' - the result is the same however with the fps figures dropping from 800 to 200 over the length of the encode. So GPU 3D utilisation drops from around 90% at the start to ~20% by the end.
Also just tried raising the priority of the Handbrake task in Task Manager to 'High' whilst encoding with no obvious effect.

[Deleted User 11865]

The Decomb filters runs on the CPU and is most likely the bottleneck here.

[dickh]

So I have just run the same file with and without the decomb filter. The rate holds up a bit longer i.e at the 30% point the fps is 680 vs 580 and at the 40% point I see 540 vs 480, however the starting figure of ~800 fps is the same on both and the final figure is ~ 260 fps on both.

[dickh]

I have just installed StaxRip which also has an Intel QSV encoder option and there does not seem to be any sign of the slowing of the encoder. Using a couple of different default quality settings I got steady rates of 700 and 550 fps - this is slightly slower than the initial Handbrake speed but a much better average rate over a 90 minute file. (NB: Some of the slowdown may be due to using the same drive for source and destination files).

This test would suggest that there is a problem with the Handbrake usage of Intel QSV rather than the Intel or FFMpeg components.