# 07 — Media (upload, download, playback)

Media travels **over the WebSocket** as chunked binary frames (decision: no
separate HTTP server; keeps the plugin to `websockets` only). Both directions
use the same chunking.

## 7.1 Kinds & MIME

`kind` ∈ `image | audio | video | document | voice`.
- `image` — `image/*` (jpg/png/webp/gif/heic).
- `audio` — `audio/*` (mp3/m4a/ogg/…) — music.
- `video` — `video/*` (mp4/webm/mov).
- `document` — anything else (pdf, docx, zip, txt, …).
- `voice` — short voice note (`audio/ogg; codecs=opus` typical).

The app sniffs `kind` from the picked file's MIME; the plugin re-sniffs on
receipt (don't trust the client) using hermes helpers
(`gateway/platforms/base.py` `_sniff_audio_ext`, `_looks_like_image`).

## 7.2 Inbound (app → agent) — `media.upload`

**Flow:**
1. App picks a file (SAF) → reads size + MIME.
2. App sends `media.upload.start {media_ref, kind, mime, size, filename}`.
3. App streams the file as **binary WS frames** (e.g. 256 KiB chunks).
4. App sends `media.upload.end {media_ref, sha256}`.
5. Plugin verifies size ≤ `max_upload_bytes` and sha256, writes to the media
   cache via hermes `cache_*_from_bytes`:
   - image → `cache_image_from_bytes`
   - audio/voice → `cache_audio_from_bytes`
   - video → `cache_video_from_bytes`
   - document → `cache_document_from_bytes`
   → returns a local path.
6. The path is attached to the next `message.send` via `media_refs`, becoming
   `MessageEvent.media_urls` + `media_types`
   (`gateway/platforms/base.py:2337`). The agent's vision/audio tools can then
   read the file.

**Limits:** `get_inbound_media_max_bytes()` / `validate_inbound_media_size`
(`base.py:758/779`) enforce the cap; over-limit → `error {code:"media_too_large"}`.

**Backpressure:** large uploads use the WS flow control; the plugin reads
binary frames into a temp file (not memory) to bound RAM.

## 7.3 Outbound (agent → app) — `media.offer` / `media.pull`

**Flow:**
1. Agent produces/references media (e.g. generates an image, or replies with a
   `MEDIA:` tag / image URL). hermes base `extract_media` / `extract_images`
   (`base.py:4439/4884`) pull these out and call the adapter's
   `send_image / send_video / send_document / send_voice / send_image_file /
   send_multiple_images`.
2. Adapter stages the file in the media cache, mints a `media_id`, and emits
   `media.offer {media_id, kind, mime, size, filename}` (inside/with the
   `message` frame's `media[]`).
3. App sends `media.pull {media_id}`.
4. Plugin streams the file as **binary WS frames**; ends with
   `media.pull.end {ok:true}`.
5. App writes to its cache dir and hands the path to the player/viewer.

**Security:** `validate_media_delivery_path` (`base.py:1684`) + the media
delivery root/recency/denied-path checks (`base.py:1312-1480`) ensure the plugin
only serves files hermes is allowed to deliver (no arbitrary file read).

## 7.4 Live playback (AI-sent music/video)

**Requirement:** play AI-sent music and video **in the app**.

- **Audio (music/voice):** `ExoPlayer` (Media3). Inline player in the bubble
  (play/pause, seek, duration); a persistent **mini-player** for music that
  survives navigation. Voice notes play inline with a waveform.
- **Video:** `ExoPlayer` inline player (play/pause, seek, fullscreen, PiP on
  Android). Streams from the local cache file after `media.pull`.
- **Documents/images:** image viewer (zoom) / open-with for documents (Android
  `Intent.ACTION_VIEW` with a `FileProvider` URI; Desktop opens with the system
  handler).
- **Desktop:** ExoPlayer is Android-only → the `MediaPlayer` expect/actual uses
  a desktop backend (see `11-desktop-app.md`): a `libmpv`/`mpv`-backed surface
  or a WebView fallback for video, and a desktop audio player for music.

## 7.5 Chunking parameters

- Chunk size: **256 KiB** (tunable). 
- Binary frames carry raw bytes only; framing/metadata is in the JSON header +
  end frames.
- Reassembly is ordered (WS preserves order); a gap/corruption → abort +
  `error {code:"internal"}` + retry the whole transfer.
- `sha256` in `media.upload.end` / a size check on pull verify integrity.

## 7.6 App-side storage

- Cache dir: app-specific external cache (`getExternalCacheDir()/media`).
- LRU eviction by size (configurable, default 500 MB) so old media doesn't fill
  the device.
- A `MediaRepository` tracks `{media_id, local_path, kind, size, ts}` in Room so
  bubbles can re-render players after process death.