Media Source CPU load: WebM vs Uncompressed MOV


New Member
Hey everyone,

We have a lot of overlays in our OBS setup, and I'm trying to make everything as CPU-efficient as I can.
I've been experimenting with the format I'm using to render things out from After Effects, and watching the effect it has on my CPU in OBS.
Everything I've been reading or watching has recommended using WebM, but whenever I do an A/B test in OBS, it always seems like uncompressed MOVs use significantly less CPU. This includes overlays with transparent elements/alpha channel.
Can anyone explain why this might be happening?



Active Member
Uncompressing compressed stuff needs CPU power but low disk i/o. Using uncompressed stuff directly needs no CPU power to uncompress but high disk i/o. Some compressed formats can be uncompressed using hardware acceleration, so they need significantly less CPU power, but some cannot. In the end, you need trial and error for the best format for you. You have to balance between three parameters: CPU load, i/o load, GPU load (for hardware decoding). What's best for you depends on the quality and dimensions (size) of your overlays, there is no general recommendation.

The less moving and animated stuff you include, the more static stuff you include, the better. If you include 3 movies that always play together, consider merging them into one movie - reading decoding one movie may bee less resource intensive than reading and decoding 3, even if the 3 together are smaller than one large.
Great question.
with storage being very inexpensive I can’t imagine it being a concern anymore. I’ve always been of the mind of, uncompressed runs smoother and keeps the cpu down... but I thought maybe thrrr was something I was missing/didn’t know about.
I was even getting better alpha channel performance via the HAP codec over the webm alpha. And surprisingly h.264 was pretty high.
I’d love to see the “money ain’t a concern” answer for the gurus