A standalone tool verifies that a stream delivers correctly — that segments arrive in order and the delivery queue does not break. It is independent of the request path; for that, see the [Streaming Subsystem](streaming-subsystem.md).
A single dependency-free tool that both **verifies** stream delivery and **renders** the result as SVG. Auto-detects HLS vs MPEG-TS. Three subcommands:
| Subcommand | Purpose |
| --- | --- |
| `check <url>` | verify one stream (or watch it live with `--live`) |
| `playlist <path\|url>` | test every stream in an `.m3u` channel list → aggregate JSON (+ per-stream files) |
| `graph <inputs…>` | render the JSON from `check`/`playlist` as static SVG charts |
| HLS (`.m3u8`) | `EXT-X-MEDIA-SEQUENCE` monotonic and contiguous (no dropped or rewound segments), no `EXT-X-DISCONTINUITY`, every newly appearing segment downloadable. Master playlists are resolved to their first variant. |
Exit code: `0` healthy, `2` queue problem or stall, `1` usage.
### Live dashboard (`--live`)
Models a virtual player: the playhead advances at wall-clock rate while content is "received". For **TS** the received timeline comes from **PCR** (the stream clock); for **HLS** from the segments' `EXTINF` durations. Buffered playtime ("cache") = received − played; if it reaches zero the playhead freezes (a rebuffer event).
IN CACHE : [█████████████████░░░░░░░░░░░░░] 11.6s / 20s
PLAYING : PLAYING head 00:18 received 00:29
rate 1000 kbit/s received 4.1 MB last data 7.0s ago
QUEUE OK cc:0 sync:0 gaps:0 disc:0 rebuffers:0
```
The buffer graph and gauge are colored green (healthy) / yellow (low) / red (starving). For HLS a row of blocks shows the segments still in cache ahead of the playhead.
> **Note — delivery pacing.** Live client delivery is now handled by the
> `xc_fanout` daemon (see [Streaming Subsystem → Daemon delivery](streaming-subsystem.md#daemon-delivery-xc_fanout)), which pulls each source once and fans it out over a unix socket. `stream_check.py check --live` visualises the buffer behaviour a real player would see against the delivered stream.
