We’re testing gaming while streaming on the R5 1500X & i5-8400 today, both CPUs that cost the same (MSRP is about $190) and appeal to similar markets. Difficulties stemming from stream benchmarking make it functionally impossible to standardize. CPU changes drastically impact performance during our streaming + gaming benchmarks, which means that each CPU test falls closer to a head-to-head than an overall benchmark. Moving between R5s and R7s, for instance, completely changes the settings required to produce a playable game + stream experience – and that’s good. That’s what we want. The fact that settings have to be tuned nearly on a per-tier basis means that we’re min-maxing what the CPUs can give us, and that’s what a user would do. Creating what is effectively a synthetic test is useful for outright component comparison, but loses resolution as a viable test candidate.
The trouble comes with lowering the bar: As lower-end CPUs are accommodated and tested for, higher-end components perform at lower-than-maximum throughput, but are capped in benchmark measurements. It is impossible, for example, to encode greater than 100% of frames to stream. That will always be a limitation. At this point, you either declare the CPU as functional for that type of encoding, or you constrict performance with heavier duty encoding workloads.
H264 ranges from Ultrafast to Slowest settings, with facets in between identified as Superfast, Veryfast, Faster, Fast, and Medium. As encoding speed approaches the Slow settings, quality enters into “placebo” territory. Quality at some point becomes indistinguishable from faster encoding settings, despite significantly more strain placed on the processor. The goal of the streamer is to achieve a constant framerate output – whether that’s 30FPS or 60FPS – while also maintaining a playable player-side framerate. We test both halves of the equation in our streaming benchmarks, looking at encode output and player output with equal discernment.
Some further testing is performed by assigning process priority to the encoding process (OBS), which can help in scheduling issues with Windows and multi-core CPUs. Affinities were tested to some extent, but ultimately cut from this content piece; we found that affinity assignment, when done optimally, largely produced the same results as High process priority given to OBS.
Stream output is 1080p60 to YouTube. Our uplink is fast enough to accommodate a low 10Mbps uprate – which is admittedly still higher than many of the world’s internet connections – and means that we’re not limited where most folks are. Of course, this also means that a lot of streamers are likely to become throttled by their ISP prior to hardware limitations, so a lot of this data interpretation comes down to the reader’s ability to keep her own situation in mind.
Most tests use the “Faster” preset, as we established that our audience prefers streaming at either “Fast” or “Veryfast,” so we picked the middle-ground. These CPUs are low-end enough that we do have to drop to “Superfast,” at times, but those charts will be demarcated as such.
Also note that a resolution drop is always possible, and will best accommodate challenged CPUs. Falling to 720p60 would reduce load significantly, as bit-rate can be reduced in-step with this. We don’t presently test 720p60, as it’s just not enough load: All the CPUs end up encoding 100% of their frames, leaving us with a benchmark that offers no real comparative data. An i9 or TR CPU would look the same, viewer-side, as an R5.
Finally, GPU encoding is always an option, but not one we’re accounting for. We’re running these tests under the assumption that the user would rather allocate this encoding workload to the CPU, either for perceived quality concerns or for increased headroom on the GPU for gaming. High-end Pascal GPUs do have two NVENC engines on them, but this is not a case accounted for in CPU tests.
For hardware used, we're on GeIL 3200MHz CL16 memory (16GB) for each platform, a Z370 Gigabyte Aorus Ultra Gaming motherboard for Coffee Lake, ASUS Crosshair VI Hero for Ryzen, a GTX 1080 FTW video card, and an EVGA SuperNova T2 1600W PSU.
The video component to this content piece includes live capture recordings from each CPU, providing a visual look at streamed output to viewers. We’d recommend watching parts of that, as it will better illustrate the differences between encoding presets and stream fluidity.
Reader FAQ: "Why not an R5 1600?"
That will come when it's time to test the higher-end i5s, like the 8600K (vs. 1600X). We went for the same price point. We previously did tests for the R7 and i7 CPUs, have tested the 8700K, i9 & TR, and wanted to get a price-to-price R5 & i5 test. We used high-end boards on each and aren't counting them toward the price. We're only interested in the CPU price matching, right now. Might do a 16-class CPU later, but not right now.