Huge thanks for `--parallel` implementation! Benchmarked results across many resolutions

[quamt]

Hi @rigaya

I just wanted to sincerely thank you for your fantastic work on QSVEnc and especially the --parallel implementation.
I ran a benchmark across a range of videos and resolutions using both HEVC and H.264, and the speed gains are massive — all while output sizes stayed consistent (or even slightly better!).

Test Setup
Test content: I used a variety of Big Buck Bunny files at resolutions from 320x180 up to 2160p60.

Extended content: Each input file was concatenated 3x using ffmpeg to simulate a longer real-world encoding task.

Comparison targets:

Codecs: --codec hevc and --codec h264

Modes: Standard vs --parallel auto

Settings:

HEVC: --profile main10 --output-depth 10

H.264: default profile (no bit-depth)

Hardware:

CPU: Ryzen 9 5950X

GPU: 2x Intel Arc A770

QSVEnc Version: 7.84 (r3665)

Results Summary:

After running all these tests, it's honestly impressive how well the --parallel implementation performs in QSVEnc.

Looking at the results, it's clear:
Whether it’s 320x180 or full 4K at 60fps, enabling--parallelgives a consistent and meaningful speed boost.
In most cases around 70–75% faster, sometimes even doubling the encode speed.

Even more impressive?
The output file sizes stayed nearly the same, with only tiny differences (sometimes even smaller!).
No need to compromise on quality or size to get that performance gain.

Amazing work, thank you again for your ongoing development!

[rigaya]

Thank you for all the tests and sharing the result!

Although having some restrictions, I think that the current --parallel implementation is an efficient way to utilize multiple GPUs at the same time with minimum compression loss.

Theoretically, using the multiple encoders with same encoding speed would result the highest efficiency, but I haven't been able to test with 2 dGPUs myself (I tested with iGPU + dGPU). Therefore, it's really nice to be able to know by your test that --parallel actually works quite efficient in terms of speedup ratio with 2x Arc A770.

Thanks again for the detailed report!

[quamt]

You're very welcome — happy to contribute and help validate such an excellent feature!

Just to add a bit more context: since I'm using two Intel Arc A770 cards, I’ve set their power limits to 110W each, not just during testing but also during the actual encoding runs. This keeps the temperatures below 65°C consistently. I haven’t measured whether this power limit has a notable impact on encoding speed, but it’s something I could look into if it helps.

Also, if it would be useful, I have access to a different system with two NVIDIA RTX 3080 cards (running at stock settings. No power limits or overclocking). I’d be happy to run similar parallel encoding tests on that machine and share the results as well.

Let me know if that’s of interest and once again, thanks for your amazing work!

[rigaya]

Arc A770 power limits

Generally, encode itself does not pull so much power (if you don't use vpp filters), so I think 110W power limit shouldn't have much impact on encoding speed.

Also, if it would be useful, I have access to a different system with two NVIDIA RTX 3080 cards (running at stock settings. No power limits or overclocking). I’d be happy to run similar parallel encoding tests on that machine and share the results as well.

Thank you for your offer! Yes, sharing results would be useful, as my NVEnc test I did when I released the first version using different GPUs (RTX4080+GTX1060) was "so-so" at 2K, only getting 30-40% boost. Although RTX4080 has 2 encoders on one card, decoder is 1, so that might be the bottleneck.

It would be nice to know whether using 2 same dGPUs like your 2x RTX 3080 system actually performs better, to know the limits of this feature.

---

Although the input is not same, my test results which I did on initial release was below.

Depending on test conditions, some performs well, but some do not, as when mixing encoders with different speed, the slower encoder limits the performance boost.

Hardware
Intel i9 12900K
Intel Arc B580 (PCIe3x4) + UHD770
NVIDIA RTX4080(PCIe4x16) + GTX1060(PCIe3x1)
Win11 24H2
QSVEnc 7.84
NVEncC 8.00 beta6

4K
input: 3840x2160 HEVC 10bit 23.976fps 17min 1sec
option: -c [h264/hevc] [--output-depth 10] [--parallel 2] --audio-copy

2K:
input: 1920x1080 MPEG2 29.97fps interlace 30min 6sec
option: -c [h264/hevc] [--output-depth 10] [--parallel 2] --audio-copy --tff --vpp-deinterlace normal

QSVEnc

			B580 single	B580+UHD770 --parallel 2
2K	H.264	8bit	357 fps	637 fps(+78%)
2K	HEVC	8bit	353 fps	636 fps(+80%)
2K	HEVC	10bit	353 fps	626 fps(+77%)
4K	H.264	8bit	147 fps	248 fps(+69%)
4K	HEVC	8bit	167 fps	215 fps(+29%)
4K	HEVC	10bit	167 fps	217 fps(+30%)

NVEncC

			RTX4080 single	RTX4080 --parallel 2	RTX4080+GTX1060 --parallel 3
2K	H.264	8bit	504 fps	733 fps(+45%)	848 fps(+68%)
2K	HEVC	8bit	484 fps	687 fps(+42%)
2K	HEVC	10bit	489 fps	618 fps(+26%)
4K	H.264	8bit	131 fps	249 fps(+90%)	250 fps(+91%)
4K	HEVC	8bit	133 fps	263 fps(+98%)
4K	HEVC	10bit	133 fps	258 fps(+94%)

[quamt]

You're very welcome @rigaya

As promised, I ran a follow-up test on the second machine equipped with 2x NVIDIA RTX 3080 cards.
This system runs at stock settings with no power limits or overclocking.

Here's a quick overview of the hardware and NVEnc version:

CPU: Intel Core i9-12900K (4.92GHz, 16C/24T)
GPU: 2x NVIDIA RTX 3080
Driver : 572.83
NVEncC: 8.03 (x64)

Like the Arc A770 setup, I tested encoding with --parallel and logged speed and file size differences.
Here’s a quick snapshot of the results:

Observations from the 2x RTX 3080 test:

Speed gains with --parallel were consistently in the 60–90% range, depending on resolution and codec.

Even at 4K, the performance boost stayed above 89% in most tests.

Like with the Arc A770s, the file size difference remained minimal or negligible, which is excellent.

Compared to your mixed RTX4080 + GTX1060 results, using two identical dGPUs (even older ones) helps avoid any performance drag from mismatched encoder speeds.

One quick question I was wondering about:

According to Intel’s specs, the Arc A770 has “2 Multi-Format Codec Engines”.
Shouldn’t that mean each card technically has 2 hardware encoders available?
Or is there a practice limitation preventing both from being used simultaneously with QSV or --parallel?

Would love to understand how that’s handled internally, if you happen to know.

[rigaya]

Thank you for the tests in NVEnc, 2x RTX3080 looks great! I'm glad to be able to know that it is quite efficient with 2 identical GPUs also in NVEnc, especially 4K speed up around 90% is quite nice.

According to Intel’s specs, the Arc A770 has “2 Multi-Format Codec Engines”.
Shouldn’t that mean each card technically has 2 hardware encoders available?

Actually I didn't notice that, but yes I also think so.

I've tested using --parallel 2 with one B580, which also said to have "2 Multi-Format Codec Engines". --parallel might be able to use the 2nd engine, as I were able to get around around 70% performance increase with --parallel. But the weird thing is that task manager or even HWiNFO reports nearly 100% video engine utilization with --parallel disabled, so I'm not sure...

Hardware
Intel i9 12900K
Intel Arc B580 (PCIe3x4)
Win11 24H2
QSVEnc 7.85

4K
input: 3840x2160 HEVC 10bit 23.976fps 17min 1sec
option: -c [h264/hevc] [--output-depth 10] [--parallel 2] -d 1 --audio-copy

2K
input: 1920x1080 MPEG2 29.97fps interlace 30min 6sec
option: -c [h264/hevc] [--output-depth 10] [--parallel 2] -d 1 --audio-copy --tff --vpp-deinterlace normal

result

			B580 single	B580 --parallel 2
2K	H.264	8bit	344 fps	607 fps(+76%)
2K	HEVC	8bit	341 fps	583 fps(+71%)
2K	HEVC	10bit	337 fps	570 fps(+69%)
4K	H.264	8bit	147 fps	206 fps(+40%)
4K	HEVC	8bit	167 fps	225 fps(+34%)
4K	HEVC	10bit	167 fps	225 fps(+35%)

[quamt]

@rigaya

I ran extended benchmarking using --parallel implementation in QSVEnc, with --parallel 4.

GPU: 2x Intel Arc A770 (1 at PCIe 4.0 x16, 1 at PCIe 4.0 x4)
I noticed you mentioned this as well, so I added it.

Observations
Performance (FPS)
Parallel 2 consistently boosted FPS by ~70–80% on average compared to normal mode. This held true across most resolutions and codecs, including 1080p and 2160p.

Parallel 4 further increased performance in some cases, but with diminishing returns. The average gain from 2x to 4x was often between 5–15% depending on resolution.

For example:

bbb_sunflower_1080p_30fps_normal_x3_h264:
Normal: 472 FPS,
Parallel 2: 868 FPS,
Parallel 4: 935 FPS

bbb_sunflower_2160p_60fps_normal_x3_hevc:
Normal: 134 FPS,
Parallel 2: 210 FPS,
Parallel 4: 286 FPS

File Size
File sizes remained very close across all modes, with only minor variations (typically under 1–2%).

This confirms the compression quality is stable even when running across multiple encoders in parallel.

System Behaviour & Side Note

When running with --parallel 4, I encountered an unusual side effect:
monitor flickering and desktop instability, which persisted after the encode completed.
A system reboot was required to fully restore normal display behaviour.

In Task Manager, I observed that one GPU completed its assigned tasks earlier, while the other continued processing.
This suggests a possible workload distribution imbalance across the two GPUs.

While I can’t conclusively attribute this to hardware limitations, my educated guess is that the PCIe x4 bandwidth constraint on one of the Arc A770 cards may be contributing to reduced throughput or uneven task allocation.
If accurate, this could help explain the diminishing performance gains observed when scaling from --parallel 2 to --parallel 4, especially in high-resolution HEVC scenarios where bandwidth and decode throughput may become critical factors.

Additionally, based on previous experience running two concurrent encodes on a single GPU, I noticed that one encode would typically operate at full speed, while the second ran at significantly reduced FPS.
This kind of encoder contention could also be influencing performance scaling in multi-GPU scenarios, particularly if multiple parallel encode sessions are unintentionally stacked on the same device.

At this time, I haven’t been able to verify whether --parallel 4 consistently distributes encoding jobs across both discrete GPUs, or if multiple sessions are sometimes assigned to a single GPU, depending on driver or API behaviour.
If there’s a way to explicitly pin sessions per device or improve task distribution across hardware, it might help optimize parallel performance further; though this may be limited by current system architecture and driver scheduling.

That said, the scaling achieved is still excellent, and any performance quirks noted here are more likely due to system-specific characteristics than QSVEnc’s implementation itself.

[rigaya]

Thank you for sharing the results for --parallel 4, it's quite interesting. I think monitor flickering might be caused by high utilization or memory usage.

As you have said, the performance gain might be limited by PCIe x4 bandwidth, or encode sessions not distributed evenly.

I've made a test build that can print which GPU is selected by each session to check out the encode session distribution. If the session are distributed equally, then the result you've shared might be the limit of the hardware(or system), but if not, I might be able to improve the GPU selection implementation by checking the log of it.
https://nightly.link/rigaya/QSVEnc/actions/runs/14334060052/QSVEncC_release_r3683_x64.zip

Below is log print of my test for --parallel 4 in this test build.

Parallel Enc 0: GPU #1 (Intel Arc B580 Graphics) score: 300.0: Use: 100.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: GPU #2 (Intel UHD Graphics 770) score: 300.0: Use: 100.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #1 (Intel Arc B580 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #2 (Intel UHD Graphics 770) score: 300.0: Use: 100.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: Selected GPU #1 (Intel Arc B580 Graphics)
Parallel Enc 2: GPU #1 (Intel Arc B580 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: GPU #2 (Intel UHD Graphics 770) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: Selected GPU #2 (Intel UHD Graphics 770)
Parallel Enc 3: GPU #1 (Intel Arc B580 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: GPU #2 (Intel UHD Graphics 770) score: 250.0: Use: 50.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: Selected GPU #1 (Intel Arc B580 Graphics)
Parallel Enc 3: Selected GPU #2 (Intel UHD Graphics 770)

In this case session 0 and 2 runs on B580, with session 1 and 3 running on UHD770.

[quamt]

Thank you

I run a few encodes here some results:

H:\QSVEnc_Output\big_buck_bunny_1080p_h264_x3_h264_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: GPU #1 (Intel Arc A770 Graphics) score: 300.0: Use: 100.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 2: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: GPU #2 (Intel Arc A770 Graphics) score: 199.9: Use: 0.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: Selected GPU #2 (Intel Arc A770 Graphics)
Parallel Enc 3: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: GPU #2 (Intel Arc A770 Graphics) score: 249.9: Use: 50.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: Selected GPU #2 (Intel Arc A770 Graphics)
Parallel Enc 2: Selected GPU #1 (Intel Arc A770 Graphics)
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

H:\QSVEnc_Output\big_buck_bunny_1080p_h264_x3_hevc_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: GPU #1 (Intel Arc A770 Graphics) score: 300.0: Use: 100.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 2: GPU #1 (Intel Arc A770 Graphics) score: 190.4: Use: 0.0, VE 100.0, GPU 90.4, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: GPU #2 (Intel Arc A770 Graphics) score: 199.9: Use: 0.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: Selected GPU #2 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 3: GPU #1 (Intel Arc A770 Graphics) score: 208.1: Use: 50.0, VE 100.0, GPU 58.1, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: GPU #2 (Intel Arc A770 Graphics) score: 186.0: Use: 0.0, VE 100.0, GPU 86.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: Selected GPU #2 (Intel Arc A770 Graphics)
Parallel Enc 3: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

H:\QSVEnc_Output\bbb_sunflower_2160p_30fps_normal_x3_h264_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: GPU #1 (Intel Arc A770 Graphics) score: 300.0: Use: 100.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 2: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: GPU #2 (Intel Arc A770 Graphics) score: 199.9: Use: 0.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: Selected GPU #2 (Intel Arc A770 Graphics)
Parallel Enc 3: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: GPU #2 (Intel Arc A770 Graphics) score: 249.9: Use: 50.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 3: Selected GPU #2 (Intel Arc A770 Graphics)
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

Each file used 4 parallel encodes.

All encoding jobs were split evenly between GPU # 1 and GPU # 2.

Than I came across this:

--------------------------------------------------------------------------------
H:\QSVEnc_Output\bbb_sunflower_2160p_30fps_normal_x3_hevc_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 1: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 2: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 3: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

In the HEVC encode of the 4K video, everything was pushed to GPU # 1.

[quamt]

I made another test run only 4K this time

H:\QSVEnc_Output\bbb_sunflower_2160p_30fps_normal_x3_h264_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: GPU #1 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 2: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: GPU #2 (Intel Arc A770 Graphics) score: 199.9: Use: 0.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: Selected GPU #2 (Intel Arc A770 Graphics)
Parallel Enc 3: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: GPU #2 (Intel Arc A770 Graphics) score: 249.9: Use: 50.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 3: Selected GPU #2 (Intel Arc A770 Graphics)
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

H:\QSVEnc_Output\bbb_sunflower_2160p_30fps_normal_x3_hevc_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: GPU #1 (Intel Arc A770 Graphics) score: 300.0: Use: 100.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 2: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: GPU #2 (Intel Arc A770 Graphics) score: 199.9: Use: 0.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: Selected GPU #2 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 3: GPU #1 (Intel Arc A770 Graphics) score: 147.6: Use: 0.0, VE 100.0, GPU 47.6, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: GPU #2 (Intel Arc A770 Graphics) score: 249.9: Use: 50.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: Selected GPU #2 (Intel Arc A770 Graphics)
Parallel Enc 2: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

H:\QSVEnc_Output\bbb_sunflower_2160p_60fps_normal_x3_h264_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: GPU #1 (Intel Arc A770 Graphics) score: 300.0: Use: 100.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #1 (Intel Arc A770 Graphics) score: 199.9: Use: 0.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 2: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: GPU #2 (Intel Arc A770 Graphics) score: 199.9: Use: 0.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: Selected GPU #2 (Intel Arc A770 Graphics)
Parallel Enc 3: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: GPU #2 (Intel Arc A770 Graphics) score: 249.9: Use: 50.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 3: Selected GPU #2 (Intel Arc A770 Graphics)
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

And same behaviour here:

H:\QSVEnc_Output\bbb_sunflower_2160p_60fps_normal_x3_hevc_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 1: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 2: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 3: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

[quamt]

test run with 1080P

H:\QSVEnc_Output\bbb_sunflower_1080p_30fps_normal_x3_hevc_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: GPU #1 (Intel Arc A770 Graphics) score: 300.0: Use: 100.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 2: GPU #1 (Intel Arc A770 Graphics) score: 184.4: Use: 0.0, VE 100.0, GPU 84.4, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: GPU #2 (Intel Arc A770 Graphics) score: 199.9: Use: 0.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: Selected GPU #2 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 3: GPU #1 (Intel Arc A770 Graphics) score: 215.7: Use: 50.0, VE 100.0, GPU 65.7, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: GPU #2 (Intel Arc A770 Graphics) score: 185.2: Use: 0.0, VE 100.0, GPU 85.2, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: Selected GPU #2 (Intel Arc A770 Graphics)
Parallel Enc 3: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

H:\QSVEnc_Output\bbb_sunflower_1080p_30fps_normal_x3_hevc_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: GPU #1 (Intel Arc A770 Graphics) score: 300.0: Use: 100.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 2: GPU #1 (Intel Arc A770 Graphics) score: 184.4: Use: 0.0, VE 100.0, GPU 84.4, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: GPU #2 (Intel Arc A770 Graphics) score: 199.9: Use: 0.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: Selected GPU #2 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 3: GPU #1 (Intel Arc A770 Graphics) score: 215.7: Use: 50.0, VE 100.0, GPU 65.7, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: GPU #2 (Intel Arc A770 Graphics) score: 185.2: Use: 0.0, VE 100.0, GPU 85.2, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: Selected GPU #2 (Intel Arc A770 Graphics)
Parallel Enc 3: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

H:\QSVEnc_Output\bbb_sunflower_1080p_60fps_normal_x3_h264_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: GPU #1 (Intel Arc A770 Graphics) score: 300.0: Use: 100.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 2: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: GPU #2 (Intel Arc A770 Graphics) score: 199.9: Use: 0.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: Selected GPU #2 (Intel Arc A770 Graphics)
Parallel Enc 3: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: GPU #2 (Intel Arc A770 Graphics) score: 249.9: Use: 50.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 3: Selected GPU #2 (Intel Arc A770 Graphics)
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

H:\QSVEnc_Output\bbb_sunflower_1080p_60fps_normal_x3_hevc_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: GPU #1 (Intel Arc A770 Graphics) score: 300.0: Use: 100.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #1 (Intel Arc A770 Graphics) score: 200.0: Use: 0.0, VE 100.0, GPU 100.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: GPU #2 (Intel Arc A770 Graphics) score: 299.9: Use: 100.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 2: GPU #1 (Intel Arc A770 Graphics) score: 186.0: Use: 0.0, VE 100.0, GPU 86.0, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: GPU #2 (Intel Arc A770 Graphics) score: 199.9: Use: 0.0, VE 100.0, GPU 99.9, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 1: Selected GPU #2 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
Parallel Enc 3: GPU #1 (Intel Arc A770 Graphics) score: 211.4: Use: 50.0, VE 100.0, GPU 61.4, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 3: GPU #2 (Intel Arc A770 Graphics) score: 185.2: Use: 0.0, VE 100.0, GPU 85.2, CC 0.0, Core 0.0, CL 0.0.
Parallel Enc 2: Selected GPU #2 (Intel Arc A770 Graphics)
Parallel Enc 3: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

And here too:

H:\QSVEnc_Output\big_buck_bunny_1080p_h264_x3_h264_parallel4.mkv
--------------------------------------------------------------------------------
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 1: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 2: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 3: Selected GPU #1 (Intel Arc A770 Graphics)
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

[quamt]

After further testing, I’ve observed some inconsistent GPU allocation behaviour when using QSVEncC with parallel encoding and multiple GPUs (Intel Arc A770 x2). While most encoding sessions correctly distribute the workload evenly across both GPUs, there are intermittent cases where all parallel jobs are assigned to only one GPU — typically GPU # 1 — even though both GPUs are fully available and report similar load and scores.

Key Observations:
This behavior does not appear to be tied to a specific codec, resolution, or frame rate.

It occurs intermittently, and not consistently at the same spot in the encode queue.

It only seems to happen when multiple encodes are run in sequence via a batch script (i.e., one after another, without pause).

In all affected cases, there are no errors or warnings in the log; the encode completes successfully, but GPU allocation is suboptimal.

This raises the question:
Could batch execution be affecting GPU resource release or initialization?

I suspect this might be the case because the issue appears to occur when encodes are launched back-to-back through a batch file, potentially without enough delay or system cleanup between jobs. It’s possible that previous processes aren’t fully releasing GPU resources, or that the Media SDK/driver hasn’t had time to reset before the next job begins.

I haven’t yet tested adding a delay between jobs in the batch script, but I plan to do so now and will report back with the results.

[quamt]

I added a 5-second delay between encodes in the batch script to ensure that GPU resources had time to release between jobs.

After running multiple 1080p encodes (which balanced GPU usage correctly), I waited manually, then started a new encode using a 4K file. In that encode, all four parallel jobs were assigned to GPU # 1, despite both GPUs being idle and available.

This suggests that:
The issue is not simply caused by the lack of delay between jobs.
GPU # 2 may still be "ignored" under certain conditions, even when idle.
The problem may be tied to driver state or prior GPU affinity lingering across sessions.

[quamt]

Question, is the build optimised for parallel 4? Because when I use parallel 2 I always get this kind of behaviour:

test.mkv
--------------------------------------------------------------------------------
Parallel Enc 1: Selected GPU #1 (Intel Arc A770 Graphics)
Parallel Enc 0: Selected GPU #1 (Intel Arc A770 Graphics)
cop.SingleSeiNalUnit value changed off -> auto by driver
QSVEncC (x64) 7.85 (r3683) by rigaya, Apr  8 2025 12:57:34 (VC 1943/Win)

[rigaya]

Thank you for the detailed tests.

When both GPUs are detected, session seem to be distributed as ideal, but it seems like somehow only 1 GPU is detected by the thread when all four parallel jobs were assigned to one GPU. The 2nd GPU "disappeared".

Whenever there is no line with "score" shown, it means that only 1 GPU is detected by the thread which runs each session.

Currently, I cannot come up of an idea of why this is happening. Maybe too many opening/closing encode session at makes GPU too busy? (as there is multiple open/close of session when starting encoding)

Could batch execution be affecting GPU resource release or initialization?

Not sure, but generally not. I've tested on my system around 50 times using bat file with --parallel 4, but could not find GPU disappearing, perhaps as the system config differs (B580 + UHD770). I think it's more likely to be a problem at initialization phase.

Question, is the build optimised for parallel 4?

No, I just added log output from QSVEnc 7.85. One more change included, but that is about AV1 encoding, I don't think it affects this problem.

[KickAss0815]

@rigaya
thank you for your great work and for improving this topic more and more. You are the best, I can't thank you enough.

Hello,

can you give me the exact ffmpeg command for the concat that you use to split the files?
Furthermore, the exact command for encoding in H264, H265 and AV1 would be helpful.

How did you do it with the listing of the results?

The reason for this is that I want to test the whole thing with my 4x Arc A310 machine and also on my 2x Arc380 machine.

It would be perfect if I could pass this on as a feature request for StaxRip. This would perfect the encoding for me.

Thanks in advance.