Technical question regarding simultaneous streaming.

[new2this]

Hello,
I have a technical question regarding OBS.
My goal is to play in 4K and use OBS to generate two streams: one to Twitch in 720p and one to YouTube in 4K.
Can I achieve this with a single OBS instance?
Will this have a major impact on performance, or will the additional 720p stream have a negligible effect?


I asked CHatGPT about this topic and wanted to make sure if its answer is correct.

Here is ChatGPT's answer:

Your Goal:​

• Play in 4K
• Stream to YouTube in 4K
• Stream to Twitch in 720p
• Ideally using a single OBS instance

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Can OBS do this with one instance?​

Not natively. OBS by default supports only one streaming output.
To stream to two platforms with different resolutions/bitrates, you need a workaround.

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Option 1: Use OBS with the "Multiple RTMP Outputs" plugin​

• Allows streaming to multiple platforms at the same time
• Each stream can have different resolution and bitrate
• Still uses one OBS instance
• May support separate encoding per stream (if you set it up that way)

Downside: If you need two different encodes, your system must handle two encoder loads (e.g., two NVENC sessions or one NVENC + one x264).

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Option 2: Run Two OBS Instances​

• One OBS instance streams Twitch in 720p
• Another OBS instance streams YouTube in 4K
• Both run independently, with their own encoder settings

Downside: Higher overall system load
You need enough CPU/GPU power and possibly two NVENC encoder sessions (e.g., available on RTX 3000/4000 series)

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About Encoder Streams (NVENC):​

• Modern NVIDIA GPUs (like RTX 3060 and up) support two or more simultaneous NVENC streams
• So you can stream 720p to Twitch and 4K to YouTube using NVENC for both, without heavy CPU load
• Using x264 for one and NVENC for the other is also an option, but puts more load on the CPU

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Summary:​

• Yes, it’s possible — either with a plugin or two OBS instances
• Two encoding streams will increase load, but if your system is strong (e.g., RTX 3070/3080, decent CPU), it’s manageable
• Plugin is easier; two instances give more control

 

[Fenrir]

Do not use ChatGPT as it cannot be trusted to provide accurate information.

 

[Lawrence_SoCal]

What Fenrir said...
but with that said, ... that summary, at a high level seems relatively consistent with my understanding.

No, no multi-stream capability exists natively (that I'm aware of), with a couple of options using either plugin or multi-instance, with each approach having its own Pro's and Con's... depends on your system, available upload bandwidth, what else is running, system load, existing or potential bottlenecks, etc ... sorry... it depends, and not necessarily a simple 'easy' answer.
Another option is to use a service like restream.io, so your encode/upload bandwidth is single stream, and that (pay) cloud service re-encodes for whatever you desire... But adding a 720p upload bandwidth wouldn't be all that much.

My bigger concern would be the reliability/stability of the multi-stream plugin. My recommendation... look into that plugin, see issues reported, asked about, etc [being aware of normal bias that in these support forums you are likely to hear of problems, and not a bunch of 'plugin works for me as expected/desired'] and then decide for yourself

 

[qhobbes]

Option 3: Run One OBS Instance with no additional plugins.

Settings > Video > Set Base and Output resolutions to 4K.
Output > Recording > Change Output Mode to Advanced. Change Type to Custom Output
Change FFmpeg Output Type to Output to URL
Input your Twitch stream URL info in the File path or URL box
Set the Container Format to mp4
Input your Twitch bitrate in the Video Bitrate box
Keyframe interval: 60 for 30 FPS, 120 for 60 FPS
Check Rescale Output and select/type 1280x720
Video Encoder: If you have NVIDIA card try h264_nvenc - NVIDIA NVENC H.264 encoder. There's also an AMD one. I used libx264...(Default Encoder) as test.
Audio Bitrate 160
Audio Track: 1 unless you use that Twitch multi-audio track thing. I don't much about that.
Audio Encoder: aac - AAC...

Apply, OK, Start Recording.

I was able to stream to my local RTMP server and view it in VLC.