What You’ll Learn

  • The basic RTMP push syntax in FFmpeg
  • Streaming to YouTube Live and Twitch
  • Encoding settings (bitrate, resolution, audio)
  • Looping a video file for broadcast-style streaming
  • Low-latency streaming configuration
  • Common errors and fixes

Tested with: FFmpeg 7.0
Platform: Windows / macOS / Linux

What is RTMP?

RTMP (Real-Time Messaging Protocol) is a video streaming protocol originally developed by Adobe. YouTube Live, Twitch, Facebook Live, and virtually every major streaming platform accept RTMP input. FFmpeg acts as an RTMP client, encoding and pushing audio/video to the RTMP server.

Basic Syntax

ffmpeg [input] [encode options] -f flv rtmp://server-url/stream-key

Use -f flv as the output format — RTMP uses FLV as its container.

Streaming to YouTube Live

Find Your Stream Key

YouTube Studio → Go Live → Stream → Copy the stream key (e.g. xxxx-xxxx-xxxx-xxxx-xxxx)

Webcam + Microphone (Linux/macOS)

ffmpeg \
  -f v4l2 -i /dev/video0 \
  -f pulse -i default \
  -c:v libx264 -preset veryfast -b:v 3000k -maxrate 3500k -bufsize 6000k \
  -pix_fmt yuv420p -g 60 -keyint_min 60 \
  -c:a aac -b:a 128k -ar 44100 \
  -f flv rtmp://a.rtmp.youtube.com/live2/YOUR_STREAM_KEY

Webcam + Microphone (Windows, DirectShow)

ffmpeg \
  -f dshow -i video="Webcam Name":audio="Microphone Name" \
  -c:v libx264 -preset veryfast -b:v 3000k -maxrate 3500k -bufsize 6000k \
  -pix_fmt yuv420p -g 60 -keyint_min 60 \
  -c:a aac -b:a 128k -ar 44100 \
  -f flv rtmp://a.rtmp.youtube.com/live2/YOUR_STREAM_KEY

Key Parameters

OptionDescription
-preset veryfastEncoding speed (use veryfast/ultrafast for real-time)
-b:v 3000kVideo bitrate
-maxrate 3500kMaximum bitrate
-bufsize 6000kBuffer size (2× maxrate is a good rule of thumb)
-g 60Keyframe interval (same as FPS = 1 keyframe per second)
-pix_fmt yuv420pYouTube-required pixel format
ResolutionFPSVideo BitrateAudio Bitrate
720p302,500–4,000 kbps128 kbps
1080p304,500–6,000 kbps192 kbps
1080p607,500–9,000 kbps192 kbps
4K3015,000–30,000 kbps256 kbps

Streaming to Twitch

Find Your Stream Key

Twitch Dashboard → Settings → Stream → Primary Stream key

ffmpeg \
  -f v4l2 -i /dev/video0 \
  -f pulse -i default \
  -c:v libx264 -preset veryfast -b:v 4500k -maxrate 5000k -bufsize 9000k \
  -pix_fmt yuv420p -g 60 -keyint_min 60 \
  -c:a aac -b:a 160k -ar 44100 \
  -f flv rtmp://live.twitch.tv/app/YOUR_STREAM_KEY

Twitch enforces a 6,000 kbps video bitrate cap. Do not exceed it.

Loop a Video File (Broadcast-Style)

Replay a pre-recorded file on loop:

ffmpeg \
  -re -stream_loop -1 -i input.mp4 \
  -c:v libx264 -preset veryfast -b:v 3000k -maxrate 3500k -bufsize 6000k \
  -pix_fmt yuv420p -g 60 \
  -c:a aac -b:a 128k \
  -f flv rtmp://a.rtmp.youtube.com/live2/YOUR_STREAM_KEY
OptionDescription
-reRead input at native framerate (required for real-time streaming)
-stream_loop -1Loop forever (-1 = infinite, 0 = no loop)

Simultaneous Multi-Platform Streaming

Use the tee muxer to push to multiple destinations with a single encode pass:

ffmpeg \
  -f v4l2 -i /dev/video0 \
  -f pulse -i default \
  -c:v libx264 -preset veryfast -b:v 3000k -maxrate 3500k -bufsize 6000k \
  -pix_fmt yuv420p -g 60 \
  -c:a aac -b:a 128k \
  -f tee -map 0:v -map 1:a \
  "[f=flv]rtmp://a.rtmp.youtube.com/live2/YT_KEY|[f=flv]rtmp://live.twitch.tv/app/TWITCH_KEY"

Desktop Capture Streaming

Linux (X11)

ffmpeg \
  -f x11grab -s 1920x1080 -r 30 -i :0.0+0,0 \
  -f pulse -i default \
  -c:v libx264 -preset veryfast -b:v 4000k -maxrate 4500k -bufsize 8000k \
  -pix_fmt yuv420p -g 60 \
  -c:a aac -b:a 128k \
  -f flv rtmp://a.rtmp.youtube.com/live2/YOUR_STREAM_KEY

macOS (AVFoundation)

ffmpeg \
  -f avfoundation -capture_cursor 1 -i "1:0" \
  -c:v libx264 -preset veryfast -b:v 4000k -maxrate 4500k -bufsize 8000k \
  -pix_fmt yuv420p -g 60 \
  -c:a aac -b:a 128k \
  -f flv rtmp://a.rtmp.youtube.com/live2/YOUR_STREAM_KEY

Low-Latency Settings

ffmpeg \
  -f v4l2 -i /dev/video0 \
  -f pulse -i default \
  -c:v libx264 -preset ultrafast -tune zerolatency \
  -b:v 2000k -maxrate 2000k -bufsize 2000k \
  -pix_fmt yuv420p -g 30 -keyint_min 30 \
  -c:a aac -b:a 128k \
  -f flv rtmp://a.rtmp.youtube.com/live2/YOUR_STREAM_KEY

-tune zerolatency combined with -preset ultrafast minimizes encoding delay at the cost of some compression efficiency.

GPU Encoding (Reduce CPU Load)

NVIDIA (NVENC)

ffmpeg \
  -f v4l2 -i /dev/video0 \
  -f pulse -i default \
  -c:v h264_nvenc -preset p4 -b:v 4000k -maxrate 4500k -bufsize 8000k \
  -pix_fmt yuv420p -g 60 \
  -c:a aac -b:a 128k \
  -f flv rtmp://a.rtmp.youtube.com/live2/YOUR_STREAM_KEY

Apple VideoToolbox (macOS)

ffmpeg \
  -f avfoundation -i "1:0" \
  -c:v h264_videotoolbox -b:v 4000k \
  -pix_fmt yuv420p -g 60 \
  -c:a aac -b:a 128k \
  -f flv rtmp://a.rtmp.youtube.com/live2/YOUR_STREAM_KEY

Troubleshooting

Connection refused / Server error

  • Your stream key is wrong — re-copy it from the dashboard
  • YouTube Live requires you to schedule or enable a stream before pushing

Video drops / choppy stream

Reduce bitrate or switch to a faster preset:

-preset ultrafast -b:v 2000k

Audio/video out of sync

-async 1

avformat_write_header: Connection timed out

Verify the RTMP URL. YouTube’s RTMP endpoint is rtmp://a.rtmp.youtube.com/live2/.

Tested with ffmpeg 7.0 / Ubuntu 24.04
Primary source: ffmpeg.org/ffmpeg-protocols.html#rtmp