CastToTV

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║  [ DLNA Caster ]           v0.5.0-beta  *  D3x  *  2026  ║
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A keygen-2005-styled DLNA caster for LG webOS TVs and generic WiFi cast dongles. Fast parallel SSDP+/24 discovery with deep port-scan fallback, on-the-fly AC3/DTS→AAC transcoding, external subtitles, pause/resume, single-file Python, ~1500 LOC, no installation.

Screenshots

Initial state — [TV] dropdown, [MODE] checkbox, PAUSE button	Fast discovery — LG webOS UP7750 detected, IP synced, dropdown populated
DONGLE WiFi probe (mid-check of dongle gateway IPs)	Mid-cast — selftest HEAD/GET, SetAVTransportURI 200, Play 200, "Streaming started!"

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TL;DR

git clone https://github.com/mikhailartamonov/CastToTV.git && cd CastToTV
python cast_to_tv.py
# Click DISCOVER → click [...] → pick a video → click <<< CAST >>>

The TV starts playing within ~2 seconds. That is the entire workflow.

Why this exists

Streaming a local file to an LG webOS TV looks like a solved problem until you actually try. VLC's renderer support hangs on subtitles. Plex needs a server. Kodi wants a remote. Web casts re-encode the entire file. Chrome's Cast extension only speaks Google's protocol.

DLNA / UPnP works on every TV in the last 15 years, but the spec is a maze and LG's implementation has five quirks no one writes down:

1. The AVTransport port randomises after every reboot — port 9197 one day, 41123 the next. So discovery has to happen every session.
2. SSDP multicast is silently dropped on many home LANs (AP isolation, IGMP snooping, guest VLAN, mesh APs) — the TV is there, just unreachable via the polite discovery path. Most casters give up here.
3. External subtitles need CaptionInfo.sec plus sec:CaptionInfoEx — both, in matching case, or the renderer ignores them.
4. Subtitles must start with a UTF-8 BOM, even though the spec doesn't require one. The decoder silently drops anything else.
5. The DMR rejects long URLs with non-ASCII bytes or spaces with UPnP 716 Resource not found — before it even tries to fetch the URL. Filename Реквием по мечте (2000).mkv simply doesn't cast.

CastToTV figures all five out automatically. The GUI is the kind of thing you used to find on a warez floppy — and that's the point.

How casting works

sequenceDiagram
    participant App as CastToTV (Tk + Python)
    participant TV as LG webOS TV
    participant HTTP as Built-in HTTP server (:8766)

    App->>TV: SSDP M-SEARCH (multicast 239.255.255.250)
    TV-->>App: HTTP/1.1 200 LOCATION: http://tv/desc.xml
    App->>TV: GET desc.xml → extract AVTransport controlURL
    Note over App: Port may differ each boot — use SSDP-advertised one

    App->>HTTP: start, serving the local file (Range-aware)
    App->>TV: SOAP SetAVTransportURI<br/>+ DIDL metadata + CaptionInfo.sec
    App->>TV: SOAP Play
    TV->>HTTP: GET /video.mp4 Range: bytes=0-
    HTTP-->>TV: 206 Partial Content + DLNA flags
    TV->>HTTP: GET /subs.srt
    HTTP-->>TV: 200 + UTF-8 BOM prepended
    TV-->>App: TransportState: PLAYING

Loading

For WiFi cast dongles (Maxscreen / AnyCast / EZCast / ElfCast) the same control plane is used, but the data plane switches to MPEG-TS in a 50 MB ring buffer because dongles can't seek raw MP4:

flowchart LR
    A[Local video file] -->|ffmpeg -c:v copy| B[MPEG-TS pipe]
    B --> C[(50 MB memory<br/>ring buffer)]
    C -->|video/MP2T| D[Dongle]
    D --> E[TV via HDMI]
    F[Audio: AC3/DTS?] -.->|yes| G[Re-encode to AAC stereo]
    G --> B
    F -.->|no| H[Copy stream]
    H --> B

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Features

• Fast unified discovery. One < DISCOVER > button runs SSDP multicast and a parallel TCP scan of the entire /24 on DLNA-relevant ports (~400 workers, ~2 s) at the same time, then dedupes by (ip, port). Found device XMLs are fetched in parallel.
• Deep port-scan fallback for hosts that don't reply to SSDP at all (LG's DMR on some firmwares is mute on 1900/udp). All 50 000 ports scanned with 800-way concurrency in ~13 s, then each open port HTTP- probed for <MediaRenderer> + <AVTransport>. Early-exit cancels the remaining probes the moment a hit lands.
• Multi-device dropdown — every renderer that came back via SSDP, port-scan or unicast lookup is listed in the [TV] combobox; pick one and the IP field syncs. Manual CONNECT adds to the same list with (ip, port) dedup.
• File-scoped HTTP server. The built-in server at :8766 only serves the exact video + optional subtitle for the active cast — any other path is 404. No directory listing, no other files leak.
• ASCII URL aliasing. Cyrillic, spaces, parens, &, long paths — none of that goes to the TV. URLs are normalised to video.mkv / subs.srt; the original filename only lives in the DIDL <dc:title> for the on-screen overlay. Fixes UPnP 716 on LG webOS.
• UPnP errorCode-aware retry. _soap_call parses <errorCode>NNN</errorCode> out of SOAP faults regardless of body length, so cast_video can auto-recover from 701 Transition not available by sending Stop then re-issuing SetAVTransportURI.
• Pause / Resume. < PAUSE > button toggles Pause / Play SOAP actions; status label and button text reflect transport state.
• Range-aware HTTP server — seek buttons (<<30s / >>10s / >>5m) use DLNA Seek SOAP for native TV-side seeking; the server itself honours Range: bytes=N-M for direct-file mode.
• External subtitles — SRT, VTT, SUB, SMI. Delivered via CaptionInfo.sec HTTP header and sec:CaptionInfoEx DIDL-Lite metadata (with sec:type + sec:URIType), and the file is served with UTF-8 BOM auto-prepended.
• On-the-fly audio transcode — AC3 / EAC3 / DTS / TrueHD / MLP get re-encoded to AAC stereo via ffmpeg pipe; video is copied losslessly. Auto-engages when probe_file flags a bad codec, or via the explicit [MODE] Force MPEG-TS checkbox.
• Dongle mode — for WiFi cast sticks, MPEG-TS in a 50 MB memory ring buffer, served as video/MP2T with transferMode.dlna.org: Streaming and DLNA.ORG_OP=00 (no Range). Seeking re-spawns ffmpeg with -ss.
• Duration in DIDL — TV remote shows the full timeline immediately instead of waiting on byte ranges to figure out the runtime.
• Socket-clean teardown. HTTPServerThread.stop() calls both shutdown() and server_close() — without that, on Windows with SO_REUSEADDR a fresh server binds alongside the dead one and Windows hands incoming SYNs to either, causing random selftest timeouts on recasts. Took an evening to figure out.
• One-click dongle WiFi reconfigure — opens the dongle's setup web UI (192.168.49.1, 192.168.203.1, 192.168.1.1) when it forgets your network.
• Debug logger — cast_log.txt next to the script, gated by the DEBUG_VERBOSE flag, captures every request, response code, DLNA header, SOAP body and access line. Saved my evening more than once.

Case studies

Case 1 — "Why does my movie play silent on the LG?"

The MKV is H.264 video + AC3 5.1 audio. LG webOS doesn't have an AC3 licence, so the renderer accepts the file, plays the video, and mutes the audio with no error.

CastToTV's probe_file reads the audio codec via ffprobe; if it's in the bad-list (ac3, eac3, dts, dca, truehd, mlp) it routes the file through ffmpeg with -c:v copy -c:a aac -b:a 128k -ac 2 and serves the resulting stream. The video is bit-for-bit identical, only the audio is re-encoded, so CPU stays low.

[FFMPEG] audio ac3→AAC
[FFMPEG] Buffering...
[FFMPEG] Ready (50MB)
[HTTP] resp 206 bytes 0-65535/9217683456 ctype=video/MP2T
[OK] Playing on LG webOS TV UP7750PTB

Case 2 — "The cast dongle won't seek"

You bought a $12 ElfCast off Aliexpress. It speaks DLNA but its firmware drops the connection any time the TV requests a Range past the first byte. So MP4 fast-start doesn't help — the dongle hangs the moment you scrub.

The fix is to never let the dongle ask for a Range. Encode to MPEG-TS (which is already a streaming format), keep the entire stream in a 50 MB ring buffer, and serve it back on a single open connection. When the user clicks >>10s, ffmpeg restarts from the new offset and the buffer resets.

That's the DongleCaster class. The dongle never sees a 206 response and never has to seek.

Case 3 — "SSDP says nothing, but the TV is right there"

You're on a guest VLAN, or your AP has client isolation, or your mesh just doesn't relay multicast properly. You can ping the TV. The TV is happily showing the YouTube screensaver. < DISCOVER > returns zero devices, every time.

The targeted /24 TCP scan still finds the host (port 7000 is open on LG webOS regardless of network state), but the SSDP follow-up to that host on 1900/udp also fails — the LG webOS DMR doesn't always reply to unicast M-SEARCH. And worse: the AVTransport service randomises its port across 1000–50000, so no fixed list catches it.

The deep-scan fallback brute-forces all ~50 000 ports in parallel (~13 s on a typical LAN at 800-way concurrency), HTTP-probes each open port for the MediaRenderer + AVTransport device descriptor, and short-circuits the moment one matches. Total time: ~15 s from click to populated dropdown, with <errorCode> parsing for clean diagnostics on the way.

[FAST] discover on 192.168.100.0/24 — SSDP + port scan
[LAN] 192.168.100.0/24: 1 host(s) with DLNA ports open
[SSDP] 0 reply(s), 0 unique location(s)
[FAST] 1 host(s) without SSDP reply — unicast probe
[FAST] 1 host(s) need deep scan (no SSDP)
[DEEP] 192.168.100.28: 16 open port(s)
[DEEP] 192.168.100.28:1451 → [LG] webOS TV UP7750PTB
[OK] 1 renderer(s) in 17.1s

Case 4 — "UPnP 716, but the URL works in my browser"

Your filename is Реквием по мечте - Requiem for a Dream (2000).mkv. The URL after quote() is 219 characters long with %D0...%29 runs and spaces. Selftest HEAD → 200. TV: <errorCode>716</errorCode> Resource not found — and the TV never even sent a HEAD to your server.

LG's DMR validates the URL string before fetching. Long URLs, Cyrillic bytes and parens trip it. The fix is to only ever hand the TV an ASCII alias (video.mkv, subs.srt) and have the HTTP server map that alias to the actual on-disk path. The Russian filename still appears on the TV's overlay via <dc:title> in DIDL — only the URL is sanitised.

Quick start

python cast_to_tv.py

1. < DISCOVER > — SSDP + parallel /24 TCP scan + deep port-scan fallback, all in one click. Found renderers populate the [TV] dropdown. (Or paste an IP and CONNECT for a single host.)
2. [...] next to [FILE] — pick a video.
3. [...] next to [SUBS] — optional, attach a subtitle.
4. [MODE] Force MPEG-TS — optional, tick if you're casting to a dongle or know your audio is AC3/DTS. (Auto-engaged on bad-codec detect anyway.)
5. <<< CAST >>>. Use < PAUSE > / < STOP > for transport control; the seek bar (<<30s / <<10s / >>10s / >>30s / >>5m) works during playback.

Build a Windows executable

pip install pyinstaller
build.bat

Output: dist\CastToTV.exe — single file, ~15 MB, UPX-compressed, no Python required on the target machine.

A tagged push to GitHub also runs .github/workflows/build.yml which attaches the same .exe to a release.

Compatibility

Receiver	Mode	Notes
LG webOS UP7750 (tested)	DLNA AVTransport	H.264/AAC plays without transcode. AC3/DTS audio auto-recodes.
LG webOS, older models	DLNA AVTransport	Same behaviour. Subtitle BOM trick is mandatory.
Maxscreen / AnyCast / EZCast / ElfCast dongles	MPEG-TS over HTTP	Auto-switches to DongleCaster ring buffer on detect.
Samsung / Sony Bravia	DLNA AVTransport	Untested, same UPnP profile so should work.
Chromecast	(not supported)	Different protocol stack — out of scope.

Requirements

• Python 3.10+ — tkinter ships with the standard distribution.
• ffmpeg / ffprobe on PATH — required for transcode and dongle modes. Without them the app falls back to direct file serving (works for plain H.264/AAC, fails for AC3/DTS sources).
• Network reachability to the TV — same /24, no isolation between WiFi clients.
• Windows for the chiptune music (winsound.Beep); on Linux/macOS the music button silently no-ops.

Project layout

.
├── cast_to_tv.py           main app: Tk GUI + HTTP server + DLNA SOAP
├── CastToTV.spec           PyInstaller spec
├── build.bat               one-shot Windows build
├── docs/
│   ├── images/             screenshots
│   ├── capture_screenshots.ps1  helper: launch GUI + grab window PNG
│   ├── interactive_capture.ps1  helper: timed capture for click flows
│   └── auto_capture.py     pyautogui colour-driven capture (best-effort)
├── legacy/                 January prototypes — pre-repo origin
│   ├── README.md
│   ├── dlna_cast.py        2025-12-31 — first SOAP cast
│   ├── cast_to_lg.py       2026-01-04 — added nmap port discovery
│   └── dlnap.py            cherezov/dlnap v0.15 (vendored, MIT)
└── .github/workflows/      tag-driven .exe build

The legacy/ folder preserves the three hand-written scripts from the New Year's weekend the project actually started. See its own README for which design choices in cast_to_tv.py descend from each one.

Roadmap

• SSDP discovery (replaced January's nmap port-scan trick)
• Range-aware HTTP server with seek
• AC3/DTS → AAC auto-transcode
• WiFi cast dongle MPEG-TS mode
• Dongle WiFi reconfigure shortcut
• File-based debug logger
• Fast parallel SSDP + /24 TCP scan unified into one click (v0.5.0)
• Deep port-scan fallback for SSDP-dead LANs / LG ephemeral port (v0.5.0)
• Multi-device dropdown (v0.5.0)
• File-scoped HTTP server — no directory listing (v0.5.0)
• ASCII URL aliasing — Cyrillic/spaces/parens stop tripping 716 (v0.5.0)
• UPnP errorCode-aware retry on 701 Transition not available (v0.5.0)
• Pause / Resume button (v0.5.0)
• Headless / CLI mode (--cast file.mp4 --to 192.168.x.y)
• Subtitle styling overrides (currently TV defaults)
• Chromecast — separate protocol stack, may never happen

License

MIT — do whatever, no warranty.

legacy/dlnap.py is by Pavel Cherezov, also MIT-licensed, copied verbatim from cherezov/dlnap.

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_{If you fix something here that helped you, drop a PR — even a typo. The project is small enough that it's still a single afternoon to read end-to-end.}