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B-frames are video frames that can improve compression by referring to other frames, but conventional bidirectional B-frames may add encoding delay because the encoder looks ahead and reorders frames. For ordinary quality-focused streaming, use them if your encoder and destination support them. For interactive, very low-latency streams, disable conventional B-frames or use a supported low-latency mode. Always check the destination’s ingest rules: Amazon IVS Real-Time, for example, disconnects OBS/RTMP streams that contain B-frames.
What B-frames do
Video codecs reduce data by predicting frames rather than encoding every frame as a complete image. A P-frame can refer to earlier frames; a conventional bidirectional B-frame can refer to frames before and after it in display order. That extra prediction can make encoding more compression-efficient, helping preserve quality at a given bitrate.
Because a conventional B-frame may depend on a future frame, the encoder can need to look ahead and reorder frames before output. That adds encoder-side latency. The size of the effect depends on the codec, encoder, settings and stream; B-frames are only one part of end-to-end delay, which also includes transmission, platform processing, buffering and playback.
Should you enable B-frames?
Choose based on your latency target, platform compatibility, encoder support, bitrate budget and hardware limits. The following are starting points, not universal presets.
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| Use case | Starting choice | Reason and scope |
|---|---|---|
| Quality-focused game or studio broadcast with ordinary viewer interaction | Enable a modest number of B-frames if the destination accepts them; test the result. | NVIDIA recommends B-frames in its game/studio and high-quality live configurations. Its examples include a two-second GOP, but that is vendor guidance, not a universal best setting. NVIDIA’s FFmpeg/NVENC guidance. |
| Interactive stream, cloud gaming, conferencing or a very tight latency target | Disable conventional bidirectional B-frames, or assess a supported unidirectional B-frame mode. | NVIDIA describes unidirectional B-frames for low-latency NVENC; they refer to past frames and avoid reordering delay. Availability depends on GPU, codec, driver and FFmpeg version. Its example requires FFmpeg 7.1 or later. NVIDIA’s FFmpeg/NVENC guidance. |
| Amazon IVS Real-Time OBS/RTMP publishing | Set B-frames to 0. | IVS says streams containing B-frames will be disconnected. This restriction is specific to the cited Real-Time OBS/RTMP instructions, not every IVS product. Amazon IVS Real-Time RTMP publishing guide. |
| Constrained GPU video memory | Consider fewer or no B-frames. | NVIDIA notes that B-frames require additional reordering buffers and advises avoiding them when reducing video-memory footprint. NVIDIA NVENC Video Encoder API Programming Guide. |
How much latency and quality difference should you expect?
AWS Elemental describes conventional B-frames as adding a few frames of latency for each additional B-frame in a GOP. In the same explanation, zero B-frames remove that reordering impact but require more bitrate to maintain similar quality. This is a qualitative vendor explanation, not a benchmark that applies to every encoder or codec; actual results depend on the preset, scene complexity, bitrate and the rest of the pipeline. AWS Elemental’s latency explanation.
NVIDIA reports 5–10% better compression than P-only encoding, with no frame-reordering delay, for its unidirectional B-frame mode and setup. Treat that as a vendor claim about that NVENC capability, not a general gain for conventional B-frames or every stream. NVIDIA’s FFmpeg/NVENC guidance.
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Removing B-frames can raise the bitrate needed for comparable visual quality. If your upload bitrate is fixed, compare the actual picture in motion—especially complex game scenes—rather than assuming a setting is better from its name alone. Also distinguish encoder delay from glass-to-glass latency: a faster encoder does not remove delay elsewhere in the delivery path.
Where the setting appears—and important distinctions
OBS with NVENC
Available options depend on the encoder and codec selected. OBS’s Advanced NVENC Options page is specifically for OBS 31.0. It describes “B-frame-as-reference” for HEVC and AV1, and recommends it when using multiple B-frames. This reference option is not the same as enabling B-frames, nor is it a general low-latency recommendation. OBS Advanced NVENC Options (31.0).
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NVENC unidirectional B-frames via FFmpeg
NVIDIA’s low-latency FFmpeg example uses -bf 0 -unidir_b 1. In that configuration, -bf 0 disables conventional bidirectional B-frames while -unidir_b 1 enables the separately supported unidirectional mode. NVIDIA’s example for 1080p30 uses a 5 Mbps target and a 167K VBV buffer; these are example values, not recommended defaults for other resolutions, frame rates or services. The guide says FFmpeg 7.1 or later is required for this example, and compatible GPU, codec and encoder support is also necessary. NVIDIA’s FFmpeg/NVENC guidance.
Keyframes and buffers are separate settings
A keyframe interval (GOP length) is not a B-frame count. Amazon IVS Real-Time’s OBS guidance recommends a 1- or 2-second keyframe interval while separately requiring B-frames to be disabled. Its cited input limits are up to 720p at 8.5 Mbps; exceeding either limit disconnects the stream. These limits apply to IVS Real-Time, not YouTube or streaming services generally. Amazon IVS Real-Time RTMP publishing guide.
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Encoder and decoder buffers also affect delay. AWS Elemental’s article describes a default encoder buffer equal to twice the video bitrate as producing a two-second decoder delay in the workflow it discusses; reducing the buffer can affect quality. That example is product- and workflow-specific, not a universal decoder rule. AWS Elemental’s latency explanation.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.A practical test before going live
- Check the destination’s current ingest requirements. Confirm supported codec, B-frame restrictions, keyframe interval, resolution and bitrate. A platform-specific rejection rule takes priority over a general encoder recommendation.
- Set a latency target. If viewers need to respond in real time, test with conventional B-frames disabled. If the stream is primarily for viewing and the platform accepts them, test the encoder’s quality-focused recommendation.
- Change one variable at a time. Keep resolution, frame rate, bitrate, preset and keyframe interval constant while comparing B-frame settings. Monitor encoder delay, dropped frames, visual quality and the delay viewers actually experience.
- Check resource headroom. If GPU memory is constrained or encoding becomes unstable, reduce B-frames or disable them and retest.
- Verify with the actual service and content. Use a representative game scene and an unlisted or otherwise controlled test stream where appropriate; confirm the destination accepts the stream and that latency meets your needs.
Common problems and fixes
- The service disconnects the stream: Check its ingest documentation for a B-frame restriction. For Amazon IVS Real-Time OBS/RTMP, set B-frames to 0.
- Viewer interaction feels delayed: Disable conventional bidirectional B-frames and test again, or use a compatible unidirectional mode. If delay remains, investigate platform, network and playback buffering rather than assuming B-frames are the only cause.
- Picture quality drops after disabling B-frames: The encoder may need more bitrate for similar quality. Check the platform’s bitrate limits and compare at a permitted bitrate before changing other settings.
- The option is missing or an FFmpeg command fails: Confirm the selected encoder, GPU, codec, driver and FFmpeg version support the requested mode. NVIDIA’s cited unidirectional example requires FFmpeg 7.1 or later and compatible NVENC support.
- GPU memory use is a concern: Reduce or disable B-frames and check whether memory headroom improves; NVIDIA identifies reordering buffers as an additional memory cost.
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