RTMP: relay drops H264 non-IDR frames before first IDR

[dkosaty]

Which version are you using?

e98b727

Which operating system are you using?

macOS amd64 standard

Describe the issue

When relaying H264 from a stream to RTMP, MediaMTX ignores non-IDR access units until the first IDR is received.

docker-compose.yml

Describe how to replicate the issue

1. start the MediaMTX
2. publish with ffmpeg
3. read with ffprobe/vlc

MediaMTX configuration

default configuration

MediaMTX logs

2026/07/10 13:07:53 INF MediaMTX v1.19.2-9-e98b7272-dirty, darwin, arm64
2026/07/10 13:07:53 INF configuration loaded from /Users/gpm/Documents/mediamtx/mediamtx.yml
2026/07/10 13:07:53 INF [RTSP] started with listeners on :8554 (TCP/RTSP), :8000 (UDP/RTP), :8001 (UDP/RTCP)
2026/07/10 13:07:53 INF [RTMP] started with listener on :1935 (TCP/RTMP)
2026/07/10 13:07:53 INF [HLS] started with listener on :8888 (TCP/HTTP)
2026/07/10 13:07:53 INF [WebRTC] started with listeners on :8889 (TCP/HTTP), :8189 (UDP/ICE)
2026/07/10 13:07:53 INF [SRT] started with listener on :8890 (UDP/SRT)
2026/07/10 13:07:53 INF [MoQ] started with listeners on :8892 (TCP/HTTP2), :8892 (UDP/HTTP3)
2026/07/10 13:07:56 INF [RTMP] [conn 127.0.0.1:57896] opened
2026/07/10 13:07:57 INF [path live/stream] stream is available and online, 2 tracks (H264, MPEG-4 Audio)
2026/07/10 13:07:57 INF [RTMP] [conn 127.0.0.1:57896] is publishing to path 'live/stream'
2026/07/10 13:08:00 INF [RTMP] [conn [::1]:57920] opened
2026/07/10 13:08:00 INF [RTMP] [conn [::1]:57920] is reading from path 'live/stream', 2 tracks (H264, MPEG-4 Audio)

Packet dump

No response