Capture cards (SDI / HDMI) and FM / DAB+ radio as sources
Updated 27 Oct 2026A channel's source can also be a device in the server: an SDI or HDMI capture card, or an SDR receiver (an RTL2832U USB stick) that picks up FM or DAB / DAB+ radio. Choose it in the channel editor like any other source; it can also be a backup source behind an IP or DVB one.
Available since Castreon 3.0.0, in all editions.
Capture card (SDI / HDMI)
Channel editor → Sources → Type: Capture card (SDI / HDMI), then:
- Card type — V4L2 (HDMI / SDI / USB) for cards and USB grabbers with a Linux video driver, or DeckLink for SDI / HDMI cards with Desktop Video installed (the server's FFmpeg must be built with DeckLink; the editor tells you if it is not).
- Card —
/dev/videoNfor V4L2; for DeckLink, choose the card by its name from the list. - Resolution and Frames/s — empty = what the card delivers.
- Card format (V4L2) —
yuyv422,nv12,mjpegorh264; empty = the default of the card. - Audio — the capture's sound card (ALSA), or no audio. With DeckLink the sound comes embedded in SDI.
Frames arrive uncompressed, so the channel is encoded on the server — a “copy” profile comes out as H.264. Pick a profile with the resolution and bitrate you want, with NVENC if the server has an NVIDIA card. A card is used by one channel at a time.
FM radio
Type: FM radio (SDR):
- Frequency in MHz (for example
98.5). - Receiver — which SDR stick, from 0 when there are several.
- Gain in dB — empty = automatic; PPM — the stick's oscillator correction, if the station is slightly off.
Castreon starts rtl_fm (package rtl-sdr) for the station and takes its sound (48 kHz, mono). One stick receives one FM station at a time.
DAB / DAB+ radio
Type: DAB / DAB+ radio (SDR):
- Block — the DAB ensemble, for example
12B,5C,13F. - Programme — the service ID (
0x4FB1) or the exact name as the ensemble announces it. - Receiver — empty = the first stick;
rtl_tcp,host:portfor a stick on another machine. - Gain — empty = automatic.
Castreon starts welle-cli (package welle.io) once per block and stick; several channels from the same block share one stick.
How radio goes out
FM and DAB sources have no picture: the channel shows its “no signal” image (or a black screen) with the radio sound encoded as AAC, so it plays everywhere — HLS, HTTP-TS, players, set-top boxes. For a radio-only channel, choose the Radio type of the channel instead: then only sound goes out.
The same Audio only switch exists on any other source (for example an internet radio stream used as a backup for a TV channel): the channel stays on air with its “no signal” image.
Installing the tools
On Ubuntu / Debian: sudo apt install rtl-sdr welle.io. On Rocky / RHEL, rtl-sdr comes from EPEL; welle-cli may have to be built from its source. If a tool is missing, the editor says so under the source. Other paths can be set in /etc/castreon/castreon.json with rtl_fm and welle_cli.
Keep the SDR sticks away from the server's fans and use a proper outdoor antenna — reception quality is decided by the antenna, not by Castreon.