...reader is too slow, discarding XX frames. On Raspberry Pi 4 and Zero 2

[7789userxyz]

Which version are you using?

v1.15.2

Which operating system are you using?

raspi-os bookworm arm64

Describe the issue

Fresh installed Raspbian Bullseye/Bookworm/Trixie arm64 on Pi Zero 2 W or Pi 4. I am setting up a minimal configuration to use the Pi camera (source: rpiCamera).
After starting mediamtx in commandline it says INF [path cam] [RPI Camera source] ready: 1 track (H264)
When starting watching the livestream via browser, phone, etc. the stream is running perfectly with alsmost zero delay. After a randome time ( sometimes 5 mins sometimes 20 mins) of watching the stream the picture starts to get buggy and the Pi terminal gives the following ...

2025/10/14 22:10:30 INF [WebRTC] [session a3f0d983] peer connection established, local candidate: host/udp/2a02:6d40:237d:8e01:aa15:f6a1:49d9:db0d/8189, remote candidate: prflx/udp/2a02:6d40:237d:8e01:316e:318d:b76:1c7c/48883
2025/10/14 22:10:30 INF [WebRTC] [session a3f0d983] is reading from path 'cam', 1 track (H264)
2025/10/14 22:10:32 WAR [WebRTC] [session a3f0d983] reader is too slow, discarding 10 frames
2025/10/14 22:10:33 WAR [WebRTC] [session a3f0d983] reader is too slow, discarding 440 frames
2025/10/14 22:10:34 WAR [WebRTC] [session a3f0d983] reader is too slow, discarding 446 frames
2025/10/14 22:10:35 WAR [WebRTC] [session a3f0d983] reader is too slow, discarding 450 frames
2025/10/14 22:10:36 WAR [WebRTC] [session a3f0d983] reader is too slow, discarding 447 frames
2025/10/14 22:10:37 WAR [WebRTC] [session a3f0d983] reader is too slow, discarding 147 frames
2025/10/14 22:10:42 WAR [WebRTC] [session a3f0d983] reader is too slow, discarding 126 frames

A few seconds later, WebRTC becomes unavailable and the Pi crashes completely, requiring a restart.
This was tested on two factory-new Pi Zero 2 (Bullseye, Bookworm and Trixie) with three different versions of PiCam (the original Raspberry Pi camera). Wifi connection and speed can be excluded.

Also tried to change the readTimeout but no difference.

I have no idea what else to try or how to fix for raspberry pi zero 2 W and Pi 4.

Describe how to replicate the issue

Just installing mediamtx on Raspberry pi Zero 2 with fresh Bookworm.
Run mediamtx and watching webrtc stream via Browser for some minutes.

MediaMTX configuration

###############################################

Only changes i made in mediamtx.yml

paths:
cam:
source: rpiCamera

[leeprevost]

I can confirm same problem.

Oct 21 21:49:06 raspberrypi mediamtx[1077]: 2025/10/21 21:49:06 WAR [WebRTC] [session e335fd11] reader is too slow, discarding 160 frames (log full of these).

but, I'm also noticing this to correlate with when I turned on the rtsp server. I think it may also be related to a buildup when internet connection degrades.

api: yes
rtmp: no
rtsp: yes
hls: no
srt: no
playback: yes

paths:
cam:
source: rpiCamera
recordPath: /home/pi/recordings/%path/%Y-%m-%d_%H-%M-%S-%f
rpiCameraWidth: 800
rpiCameraHeight: 600
rpiCameraBitrate: 5000000

[PlaneNuts]

I came across this project yesterday and was getting this error when testing out reading an RTMP stream in OBS. When reading through the docs (https://github.com/bluenviron/mediamtx/blob/main/docs/2-usage/26-decrease-packet-loss.md) on the github page I came across

• When reading a stream, packets might get discarded because the write queue is too small. This can be noticed in logs through the "reader is too slow" message. Try increasing the write queue:

  writeQueueSize: 1024

Setting a higher value than the default solved this for me

[aler9]

One solution is the one suggested by @PlaneNuts.

The other solution is to monitor the bandwidth between the Raspberry and intended users and make sure that it's enough to account for the intended usage. Don't expect to serve a 5 Mbps stream to 20 users with a 2.4 ghz WiFi. Decrease the bandwidth or improve the WiFi.