For a 60fps YouTube Live stream, target a keyframe every 2 seconds: that is 120 frames at a constant 60fps. YouTube recommends a 2-second interval and says not to exceed 4 seconds. With FFmpeg’s libx264 encoder, start with -g 120; for a more regular cadence, consider -keyint_min 120 and -sc_threshold 0. YouTube also specifies a closed GOP for optimal transcoding, so verify the behavior of the encoder you actually use rather than treating those flags as proof of a closed GOP.
Why the 60fps setting is 120 frames
YouTube expresses its recommendation in time: a keyframe frequency of 2 seconds, with a maximum interval of 4 seconds. FFmpeg’s -g setting expresses maximum GOP size in frames. At a constant output rate of 60 frames per second:
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- 2 seconds: 60 × 2 = 120 frames. This is the target.
- 4 seconds: 60 × 4 = 240 frames. This is YouTube’s stated ceiling, not the recommended target.
A 60-frame GOP at 60fps is only 1 second. The 120-frame value follows from the two-second target; it is not the same value used for a two-second interval at 30fps. YouTube’s interval guidance and closed-GOP requirement are in its live encoder settings guidance and live-stream error guidance.
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For a known, constant 60fps output encoded with libx264, these are GOP-related starting options:
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-g 120 -keyint_min 120 -sc_threshold 0
For example, in a larger command:
ffmpeg -i INPUT -c:v libx264 -g 120 -keyint_min 120 -sc_threshold 0 ... OUTPUT
This is not a complete YouTube streaming command: the ellipsis stands for the output destination and the other choices your stream needs, including rate control, audio, pixel format, and output frame rate. The example communicates the GOP intent; it has not been tested as a complete command.
-g 120sets the maximum GOP size to 120 frames in the libx264 wrapper. At 60fps, that is a two-second maximum interval.-keyint_min 120sets the minimum keyframe interval for libx264. Pairing it with-g 120can support a regular interval.-sc_threshold 0disables scene-cut keyframe insertion for libx264, which can help avoid scene cuts interrupting the cadence.
These options are documented in the FFmpeg codec documentation. Encoder choices and builds can differ; check the options supported by your selected encoder and inspect the resulting stream. Do not assume libx264 flags apply to a hardware encoder or establish its GOP structure.
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Alternative: force keyframes by time
FFmpeg also documents a timestamp-based option:
-force_key_frames 'expr:gte(t,n_forced*2)'
The expression asks FFmpeg to force a keyframe on a two-second time cadence. FFmpeg’s command documentation explains that requested timestamps are rounded to the nearest output timestamp, and the first frame at or after the computed time is selected. Frame timestamps and the encoder time base therefore affect where keyframes land.
This is an alternative control, not a guarantee that every GOP has an exact fixed length or is closed. Inspect the output and confirm the chosen encoder’s closed-GOP behavior separately.
Closed GOP and encoder verification
YouTube Help says, “YouTube’s pipeline requires a Closed GOP for optimal transcoding.” A GOP interval setting specifies timing or length; it does not, by itself, prove that the encoded GOP is closed. The relevant option and its meaning depend on the encoder. Confirm that your selected encoder can produce the needed structure, consult its documentation, and verify the output rather than assuming one FFmpeg flag covers every encoder.
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YouTube also notes that ingestion errors can cause incorrectly reported GOP sizes. Check stream health in YouTube Live Control Room and test with representative motion and audio, as YouTube advises in its live-stream error guidance.
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The keyframe interval is only one part of the stream configuration. YouTube’s live encoder settings list H.264, H.265/HEVC, and AV1 for RTMP/RTMPS, support up to 60fps, recommend RTMPS, and list progressive scan and two B-frames among its advanced settings. The recommended H.264 bitrates below are separate from the GOP interval:
| Output resolution | YouTube recommended H.264 bitrate at 60fps |
|---|---|
| 1080p60 | 17 Mbps |
| 1440p60 | 34 Mbps |
| 2160p60 | 50 Mbps |
Match bitrate to resolution and codec using YouTube’s current live encoder settings; do not treat these bitrate values as keyframe settings or apply the H.264 figures automatically to other codecs.
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Check variable frame rate and output cadence
The 120-frame calculation assumes the encoded output is constantly 60fps. A variable-frame-rate source, dropped frames, frame-rate conversion, or a different output frame rate can change the relationship between frame counts and elapsed time. Set the intended output cadence in the full FFmpeg command and verify the actual stream. If your output is not constant 60fps, do not assume -g 120 will correspond to exactly two seconds throughout.
Troubleshoot keyframe and GOP problems
- GOP interval is twice as long as expected: Check the output frame rate. At 30fps, 120 frames spans 4 seconds; the two-second target at that rate is 60 frames.
- Scene changes create extra keyframes: For libx264, consider
-sc_threshold 0alongside the GOP options, then inspect the encoded output. Other encoders may use different controls. - Keyframes do not land exactly every two seconds: Check output timestamps, frame-rate conversion, and encoder time base. With
-force_key_frames, FFmpeg rounds to output timestamps, so exact timing depends on the output cadence. - YouTube reports an unexpected GOP size: Check stream health in Live Control Room. YouTube warns that ingestion errors can produce incorrect GOP-size reports.
- The stream has a regular interval but transcoding is still problematic: Verify closed-GOP support and configuration for the selected encoder. A regular interval alone does not establish closed-GOP structure.
- The stream is unstable or quality is poor: Review codec, bitrate, resolution, frame rate, scan type, B-frames, and RTMPS settings independently of the keyframe interval against YouTube’s encoder guidance.
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