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constant frame rate

How to Stream a Video File to YouTube Live at a Constant Frame Rate with FFmpeg

A practical FFmpeg workflow for converting prerecorded video to a constant-frame-rate YouTube Live stream, with keyframe, bitrate and troubleshooting guidance.

By VGSources Team 6 min read

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To stream a video file to YouTube Live at a constant frame rate (CFR), have FFmpeg read the file in real time, transcode it to your chosen output frame rate, and send it to YouTube using the stream URL and key shown in YouTube Studio. For example, -vf "fps=30" converts the output to 30 fps by dropping or duplicating frames as needed. Use a two-second keyframe interval—60 frames at 30 fps—and a bitrate suited to your resolution, frame rate, and stable upload bandwidth.

Stream a video file to YouTube Live with FFmpeg

This example loops a file indefinitely, converts its video to 30 fps, and sends H.264 video and AAC audio over RTMP. It is a starting point, not a tested command: adapt the video bitrate and confirm that your FFmpeg build includes libx264.

ffmpeg -re -stream_loop -1 -i input.mp4 
  -vf "fps=30" 
  -c:v libx264 -preset veryfast -pix_fmt yuv420p 
  -b:v 10M -maxrate 10M -bufsize 20M 
  -g 60 -keyint_min 60 -sc_threshold 0 
  -c:a aac -b:a 128k -ar 44100 
  -f flv "rtmp://SERVER/STREAM_KEY"
  1. Prepare the live stream in YouTube Studio. Create or open the live stream and copy its server URL and stream key. Replace rtmp://SERVER/STREAM_KEY with the values YouTube supplies. Treat the key like a password: do not publish it or share it.
  2. Choose your input file and loop behavior. Replace input.mp4 with the file path. -stream_loop -1 repeats the file indefinitely; remove that option if the live output should end when the file ends.
  3. Set the output frame rate. -vf "fps=30" asks FFmpeg to produce 30 frames per second, dropping or duplicating frames as needed. Choose an output cadence appropriate to your content and stream plan.
  4. Set the video encoding and bitrate. The example encodes H.264 using libx264, the veryfast preset and yuv420p. Its 10 Mbps video bitrate is YouTube’s listed H.264 recommendation for 1080p30 live ingestion, not a universal setting. Change it for your chosen resolution and frame rate, and ensure your connection can sustain the stream bitrate.
  5. Set keyframe timing. At 30 fps, -g 60 sets a 60-frame GOP, or two seconds. The matching -keyint_min 60 and -sc_threshold 0 settings support a regular interval with this x264 example.
  6. Start FFmpeg and check the live preview. Watch YouTube Studio’s stream health and verify that video, audio, frame rate and timing are as expected before sharing the live stream.

-re makes FFmpeg read the file at its native playback speed instead of sending it as fast as it can process it. -f flv selects the container used for this RTMP example. YouTube’s live encoder guidance covers RTMP/RTMPS and recommends H.264, H.265/HEVC or AV1, with frame rates up to 60 fps. This example uses H.264 as a straightforward profile. See YouTube’s live encoder settings and bitrate recommendations.

Choose the frame rate and keyframe interval together

YouTube recommends a two-second keyframe interval and says not to exceed four seconds. GOP size is measured in frames, so the frame rate determines the GOP length for a given interval.

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Output frame rate GOP for a two-second interval
25 fps 50 frames
30 fps 60 frames
60 fps 120 frames

For another frame rate, multiply frames per second by two to get a two-second GOP. The example command’s -g 60 is correct for 30 fps, not for every output cadence. YouTube also documents live errors related to frame rate and keyframe timing in its live streaming error messages.

Set bitrate to match resolution, frame rate and connection

For H.264 live ingestion, YouTube lists these recommended video bitrates:

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Output YouTube-listed H.264 recommendation
720p30 8 Mbps
1080p30 10 Mbps
1080p60 17 Mbps

These are platform recommendations, not a guarantee that your upstream connection can hold the bitrate reliably. Leave bandwidth headroom for audio and network variation, and test on the connection you will use for the event. YouTube’s live guidance recommends CBR for live bitrate mode. In the example, -b:v, -maxrate and -bufsize are illustrative encoder controls; they do not guarantee constant instantaneous bitrate. Confirm your encoder’s actual rate-control behavior and adjust for the target profile.

The example audio settings encode AAC stereo at 128 kbps and 44.1 kHz. Check the live preview for intelligible, synchronized audio as well as a healthy video signal.

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Make variable-frame-rate footage constant-frame-rate

For a CFR transcode, specify the desired output frame rate. FFmpeg’s -vf "fps=30" filter creates a 30-fps cadence by dropping or duplicating frames. Output -r 30 can also request an output rate by duplicating or dropping frames before encoding; the filter makes the conversion explicit in the video filter chain.

Do not casually put input -r 30 before an ordinary video file as a CFR fix. FFmpeg documents input -r as ignoring stored timestamps and generating timestamps at the specified rate, a behavior intended for raw formats. For a normal file, use an output conversion instead. Likewise, -c:v copy stream-copies the existing encoded frames; it does not create a new constant frame cadence from arbitrary variable-frame-rate footage. These options have distinct timestamp and frame-handling behavior in the FFmpeg documentation.

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Do not confuse a live stream with a normal upload

A live stream is sent in real time to YouTube’s live ingest using a stream URL and key. You choose an output cadence, keyframe interval, live protocol, codec and sustained bitrate for that stream. A normal upload is a file processed after you send it; YouTube’s upload guidance says to encode and upload at the frame rate at which the content was recorded, and lists common rates including 24, 25, 30, 48, 50 and 60 fps.

Workflow Destination and timing Frame-rate approach Relevant settings
File playout as a live stream Live ingest; file is played in real time Choose a live output cadence; transcode if needed for CFR Stream key, protocol, keyframe interval and sustainable live bitrate
Ordinary video upload Upload processing; create the file offline Use the recording frame rate, per YouTube’s upload guidance File/container and upload encoding recommendations

For an ordinary upload, follow YouTube’s recommended upload encoding settings rather than treating live-ingest settings as a general export recipe. That guidance includes MP4, H.264 and progressive scan recommendations.

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Test before the stream and troubleshoot problems

YouTube recommends testing with similar audio and movement before going live, then monitoring stream health during the event. A static test image alone may not reveal cadence or motion issues.

  • YouTube reports an unsuitable frame rate: Confirm that the command uses an output conversion such as -vf "fps=30", and that the stream is encoded rather than stream-copied. Check the selected output profile and YouTube Studio’s stream health.
  • YouTube reports a keyframe interval issue: Recalculate the GOP in frames for the actual output rate. For example, a two-second interval at 60 fps requires 120 frames, not 60.
  • The connection cannot keep up: Reduce resolution, frame rate or video bitrate to a level your upstream connection can sustain. YouTube’s recommended bitrate is not proof of available bandwidth at your location.
  • FFmpeg says the encoder is unavailable: The command assumes the installed build includes libx264. Use a build with that encoder or select an available compatible encoder and verify its rate-control and keyframe options.
  • The stream ends when the file finishes: Keep -stream_loop -1 to repeat indefinitely, or omit it when ending at the file boundary is intended.
  • YouTube does not receive the stream: Recheck the server URL and stream key copied from YouTube Studio, confirm the selected protocol and inspect FFmpeg’s output for connection errors. Regenerate or replace a key if it has been exposed.

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