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UDP Pipelines

End-to-end MPEG-TS streaming of H.264 video with MISB ST 0601.8 KLV metadata over UDP.

Quick Start

Python

Receiver first:

python3 examples/udp-pipelines/python/udp_receiver_93tags.py \
  --host 0.0.0.0 --port 5000

Then sender:

python3 examples/udp-pipelines/python/udp_sender_93tags.py \
  --host 127.0.0.1 --port 5000 --count 50

C++

cmake -S . -B build -DGSTKLVPLUGIN_BUILD_EXAMPLES=ON
cmake --build build

The C++ example binaries are built via CMake. Meson still builds the plugin and tests, but not the example executables.

Receiver first:

./build/gstklv_udp_receiver --host 0.0.0.0 --port 5000

Then sender:

./build/gstklv_udp_sender --host 127.0.0.1 --port 5000 --count 50

Transport Notes

  • Sender still uses mpegtsmux alignment=7, so TS leaves in 1316-byte network-friendly buffers.
  • Receiver uses udpsrc with MPEG-TS caps: video/mpegts, systemstream=true, packetsize=188.
  • PMT signaling is the same as the SRT examples because the transport differs, not the mux/signaling path.
  • The receiver keeps video and decoded-KLV output clock-synchronised, so terminal prints follow the visible frame instead of a separate metadata-only timeline.

Pipeline Composition

Sender

flowchart LR
    A["videotestsrc"] --> B["videoconvert"]
    B --> C["x264enc"]
    C --> D["h264parse"]
    D --> E["klvframeinject"]
    E -->|video_src| F["queue"]
    F --> G["mpegtsmux<br/>alignment=7"]
    E -->|klv_src| H["queue"]
    H --> I["meta/x-klv<br/>parsed=true<br/>stream-format=klv<br/>stream-type=21"]
    I --> G
    G --> J["tspmtrewrite"]
    J --> K["udpsink"]
Loading

Receiver

flowchart LR
    A["udpsrc<br/>caps=video/mpegts"] --> B["tsdemux"]
    B -->|video/x-h264| C["queue"]
    C --> D["h264parse"]
    D --> E["avdec_h264"]
    E --> F["videoconvert"]
    F --> G["videosink"]
    B -->|meta/x-klv| H["queue"]
    H --> I["klvmetadec"]
    I --> J["fakesink / appsink"]
Loading

Practical note:

  • --print-summary gives the most stable live preview.
  • --print-all is still useful for debugging, but console throughput can become the limiting factor before the transport does.

PMT Signaling

The UDP examples use the same tspmtrewrite behavior as the SRT examples:

  • stream_type = 0x06
  • registration_descriptor = KLVA
  • metadata_descriptor (0x26) = present

That is the current repo behavior because it works with GStreamer tsdemux for raw KLV.

Troubleshooting

Symptom Resolution
Receiver prints KLV but the video window never starts Check that sender still uses mpegtsmux alignment=7, and keep the receiver decode path as h264parse ! avdec_h264 ! videoconvert ! videosink
Prints do not seem aligned to the displayed frame Keep the current receiver sync settings and prefer --print-summary when inspecting live streams

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