DJI Osmo Pocket 4 RTMP HEVC Fix for BELABOX/RK3588

A small flvdemux patch that lets BELABOX accept wireless RTMP HEVC from the DJI Osmo Pocket 4. The Pocket 4 sends HEVC inside FLV using legacy codec ID 12, which stock GStreamer 1.20.3 throws out as unsupported video codec tag 12. This patch patches flvdemux to handle codec ID 12 as H.265 so the pipeline reaches h265parse, Rockchip MPP decode and BELABOX encoding.

The original gstreamer-1.0/libgstflv.so is never touched. The patched plugin lives in /opt/belabox-pocket4-rtmp-hevc/ and BELABOX picks it up through a belaUI.service systemd drop-in.

Tested on

• BELABOX on RK3588 / Radxa ROCK 5B+
• Ubuntu Jammy base image, GStreamer 1.20.3, source gst-plugins-good1.0 1.20.3-0ubuntu1.5
• Pocket 4 stream: 1920x1080 @ 30 fps, HEVC Main, 8-bit, BT.709
• Pocket 4 publishing to rtmp://<belabox-address>:1935/publish/live

Main10 or other HEVC profiles may fail later in mppvideodec and have not been tested.

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Step 1 - Back up first

Take a rollback point before anything else. The package is built to be easy to remove, but this is still live encoder pipeline work. A full board image is best. At a minimum, keep a copy of your working BELABOX configuration.

Step 2 - Download

Download this repo:

cd /home/user/
curl -L https://github.com/Kimsec/belabox-pocket4-rtmp-hevc/archive/refs/heads/main.tar.gz | tar xz
mv belabox-pocket4-rtmp-hevc-main belabox-pocket4-rtmp-hevc

Download the GStreamer source:

apt source gst-plugins-good1.0=1.20.3-0ubuntu1.5

You should now have this layout:

/home/user/
  belabox-pocket4-rtmp-hevc/
  gst-plugins-good1.0-1.20.3/

Step 3 - Apply the patch

cd /home/user/gst-plugins-good1.0-1.20.3
patch -p1 < ../belabox-pocket4-rtmp-hevc/patches/pocket4-flvdemux-hevc-codec12.patch

If the source tree is already patched, this command may say the patch was previously applied.

Step 4 - Install build dependencies

sudo apt update
sudo apt install build-essential pkg-config dpkg-dev patch \
  libglib2.0-dev libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev

Step 5 - Build

cd /home/user/belabox-pocket4-rtmp-hevc
bash scripts/build.sh

Output: build/libgstflv.so.

Step 6 - Install

sudo bash scripts/install.sh

The script:

• copies the patched plugin to /opt/belabox-pocket4-rtmp-hevc/
• drops the custom pipeline files in the BELABOX pipelines folder
• writes the belaUI.service systemd drop-in
• clears the GStreamer registry cache
• runs daemon-reload and restarts belaUI.service

No reboot needed.

Step 7 - Verify the patched plugin is loaded

bash scripts/test-inspect.sh

You want to see:

• Filename pointing to /opt/belabox-pocket4-rtmp-hevc/libgstflv.so
• both video/x-h265, stream-format=hvc1 and video/x-h265, stream-format=byte-stream in the caps

If Filename points back to /usr/lib/aarch64-linux-gnu/..., the drop-in is not active.

Step 8 - Test live decode

Warning

Start the Pocket 4 publishing to BELABOX first.

This test reads from the live RTMP stream, so it will fail if nothing is being streamed in.

bash scripts/test-live-decode.sh

Healthy output:

• video/x-h265, stream-format=byte-stream, alignment=au reaching mppvideodec
• video/x-raw, format=NV12 on the decoder's source pad
• pipeline going to PREROLLED then PLAYING

There is also test-live-reencode.sh which adds mpph265enc to confirm the full decode-plus-encode chain. Both scripts run until you press Ctrl+C. MPP device access often needs root, so they re-run themselves through sudo if needed.

Step 9 - Use it in the BELABOX UI

Pipeline files for 25 and 30 fps are installed automatically. Picking the right one is still a manual step in the BELABOX UI.

A good real run shows:

• clean video and audio at the receiver
• no unsupported video codec tag 12
• no Delayed linking failed
• no mppvideodec errors
• bitrate control still working

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Rollback

cd /home/user/belabox-pocket4-rtmp-hevc
sudo bash scripts/rollback.sh

That removes the systemd drop-in and the custom pipeline files, clears the registry cache, reloads systemd, and restarts belaUI. The original GStreamer plugin was never replaced, so there is nothing to restore.

What is in the package

• the patch
• build, install, rollback and test scripts
• BELABOX custom pipeline files for 25 and 30 fps

There is no prebuilt libgstflv.so. You build the plugin yourself against the matching Ubuntu source.

The package does not change nginx or nginx-rtmp. The reason nginx comes up at all is diagnostic: it may not cache/replay HEVC sequence headers for legacy codec ID 12, so the fallback is handled on the GStreamer side instead.

Technical notes

What the patch actually changes in flvdemux:

• maps FLV codec ID 12 to H.265
• adds video/x-h265 to the source caps
• falls back to byte-stream mode if nginx-rtmp does not replay HEVC sequence.
• logs the fallback warning once per stream instead of once per packet
• leaves H.264 (codec ID 7) alone

Caveats

• experimental - soak test for an hour or more before relying on it
• targets legacy codec ID 12, not Enhanced RTMP ExHeader HEVC
• byte-stream fallback assumes 4-byte length-prefixed HEVC NAL units: a different legacy variant from another camera is not tested.
• watch audio sync, bitrate behaviour, reconnect handling, temperature and memory through longer testing before recommending it to anyone else. All was fine while testing on my setup.