Crash when switching H264 RTP streams using input-selector / pipeline restart (v4l2h264dec)

Application Development Embedded
1

Hi all,

I’m relatively new to GStreamer and still have a limited understanding of it. I’m trying to build an application that receives H264 RTP streams over UDP and displays them using a hardware-accelerated decoder (v4l2h264dec). However, I’m facing instability and crashes when switching between two streams.

Setup

I have two independent RTP H264 streams:

Stream 1:

gst-launch-1.0 \
  udpsrc port=8081 \
  caps="application/x-rtp,media=video,encoding-name=H264,clock-rate=90000,payload=96" \
  ! rtph264depay \
  ! h264parse \
  ! v4l2h264dec \
  ! kmssink sync=false force-modesetting=true

Stream 2:

gst-launch-1.0 \
  udpsrc port=8082 \
  caps="application/x-rtp,media=video,encoding-name=H264,clock-rate=90000,payload=96" \
  ! rtph264depay \
  ! h264parse \
  ! v4l2h264dec \
  ! kmssink sync=false force-modesetting=true

Each pipeline works correctly when run independently.

Requirement

I need to dynamically switch between these two streams (e.g., based on user interaction or events).

What I Tried

1. Pipeline restart approach

  • Stop pipeline (stream on port 8081)
  • Start pipeline (stream on port 8082)

This works initially but leads to random crashes after multiple switches.

2. input-selector approach

  • Single pipeline with two inputs
  • Switch active pad dynamically

This improves behavior but still results in instability after some time.

Observed Errors

Kernel / driver logs:

vdec 30210000.video-codec: wave5_vpu_enc_finish_encode: encoded buffer (1) was not in ready queue 0. 
vdec 30210000.video-codec: wave5_vpu_enc_finish_encode: no source buffer with index: 1 found 
vdec 30210000.video-codec: wave5_vpu_firmware_command_queue_error_check: result not ready: 0x800
vdec 30210000.video-codec: wave5_vpu_dec_finish_decode: could not get output info.

GStreamer warning:

v4l2h264dec0: Too old frames, bug in decoder -- please file a bug

Questions

  1. Is repeatedly stopping/starting pipelines with v4l2h264dec expected to cause instability?

  2. Is input-selector the recommended way to switch between RTP streams with hardware decoding?

  3. What does the "Too old frames" warning indicate in this context?

Goal

A stable solution to:

  • Keep both RTP streams active
  • Switch between them dynamically
  • Avoid decoder crashes or desynchronization

Any suggestions or pointers would be greatly appreciated.

Thanks!

2

I do not have any experience with v4l2h264dec but I am working on a similar project, and I would suggest that since you are ok with keeping both streams live at the same time, that you remove the input selector and use a compositor downstream of the decoders. With this approach you can then change settings on the compositor sink pads to show or hide a particular stream on the fly.