Title: i.MX8MP V4L2 H.264 Encoder Fails on Dynamic Runtime Update (Bitrate Mode / Resolution) — poll

VishnuSidda — Tue, 17 Mar 2026 09:00:03 GMT

Platform Details:

SoC: i.MX8MP
BSP: (Linux imx8mpevk 6.12.20-lts-next-gdfaf2136deb2)
GStreamer: 1.26.0 (NXP plugins)
Encoder: v4l2h264enc
Source: v4l2src (camera)
OS: Linux (Yocto-based)

Use Case:
We are building a dynamic multi-stream video pipeline using GStreamer with the following architecture:

v4l2src → capsfilter → imxvideoconvert_g2d → tee
                                         ├── RTSP branch (v4l2h264enc)

We dynamically create/remove encoder branches from a tee (using request pads) and support runtime configuration updates via API.

Problem Description:

We are attempting to dynamically update encoder parameters at runtime (pipeline in PLAYING state), specifically:

Bitrate mode (CBR / VBR)
Bitrate
Resolution (caps change)

This is done using:

g_object_set() on encoder (extra-controls)
Updating caps on downstream capsfilter
Updating videorate (max-rate)

Relevant Code (Simplified):

enc_el.set_property("extra-controls", Gst.Structure.new_from_string(
    "controls,video_bitrate_mode=1,video_gop_size=25"))

rate_el.set_property("max-rate", fps)

res_el.set_property("caps", Gst.Caps.from_string(
    f"video/x-raw,width={w},height={h},format=BGRx"))

Observed Behavior:

Immediately after applying dynamic update (especially bitrate mode change), pipeline fails with:

gstvideoencoder.c:2506:
Can't copy metadata because input frame disappeared

v4l2object.c:6524: gst_v4l2_object_poll:
poll error 1: Invalid argument (22)

GST_ERROR:
Could not read from resource.

gstbasesrc.c:3187:
Internal data stream error.
streaming stopped, reason error (-5)

This results in:

Encoder failure (v4l2h264enc)
Queue failure
Source (v4l2src) stopping
Entire pipeline going to error state

Full Error Logs (Excerpt):

gst_v4l2_object_poll:<v4l2h264enc> error: poll error 1: Invalid argument (22)
gst_element_message_full_with_details: Could not read from resource
gst_base_src_loop:<v4l2src> error: Internal data stream error
streaming stopped, reason error (-5)

Key Observations:

Issue is reproducible when changing:
- video_bitrate_mode (CBR ↔ VBR)
- bitrate
Sometimes encoder accepts property but:
- no visible effect OR
- fails shortly after
FPS changes using videorate work fine
Resolution changes sometimes work but are unstable

Questions:

Is runtime update of v4l2h264enc controls supported?
- Specifically:
  - video_bitrate_mode
  - video_bitrate
  - video_gop_size
Are these controls required to be set only in:
- NULL / READY state?
Does the i.MX8MP VPU driver support:
- dynamic bitrate adjustment in PLAYING state?
For resolution change:
- Is dynamic caps renegotiation supported with imxvideoconvert_g2d + encoder?
- Or is pipeline restart required?
What is the recommended approach for:
- changing bitrate mode (CBR/VBR)
- changing resolution
- in a live streaming pipeline?

Additional Context:
In commercial IP cameras, bitrate appears to change dynamically without stream interruption.
We would like to understand whether:

This is supported at driver level, or
Requires encoder restart / pipeline rebuild.

Expected Guidance:

Official recommendation from NXP for runtime encoder reconfiguration
Supported vs unsupported controls in PLAYING state
Best practice for dynamic streaming pipelines

Summary:
Dynamic updates to v4l2h264enc (especially bitrate mode) result in:

V4L2 poll errors (EINVAL)
Encoder failure
Pipeline crash

We want to confirm whether this is expected behavior and how to correctly implement dynamic reconfiguration.

Thank you.

Re: Title: i.MX8MP V4L2 H.264 Encoder Fails on Dynamic Runtime Update (Bitrate Mode / Resolution) —

joanxie — Wed, 18 Mar 2026 05:22:37 GMT

I've already mailed to you for enabling VBR, then you can control it dynamically, pls check my mail

topic Re: Title: i.MX8MP V4L2 H.264 Encoder Fails on Dynamic Runtime Update (Bitrate Mode / Resolution) — in i.MX Processors

Title: i.MX8MP V4L2 H.264 Encoder Fails on Dynamic Runtime Update (Bitrate Mode / Resolution) — poll

Re: Title: i.MX8MP V4L2 H.264 Encoder Fails on Dynamic Runtime Update (Bitrate Mode / Resolution) —