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switch to websocket for live stream (#59)

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The multipart stream / hanging GET approach worked in a prototype for a
single stream, but Chrome has a per-host limit of six connections. If I
try streaming all my cameras at once, I hit that limit. I can't open all
the streams, much less additional connections to load init segments and
such. Websockets apparently has a much higher limit of 256.
This commit is contained in:
Scott Lamb
2020-02-28 21:41:31 -08:00
parent 3fa48ab0da
commit 92266612b5
6 changed files with 223 additions and 87 deletions
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57
design/api.md
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@@ -416,17 +416,21 @@ URL minus the `.txt` suffix.
### `GET /api/cameras/<uuid>/<stream>/live.m4s`
Returns a `multipart/mixed` sequence of parts. An extra top-level header,
`X-Open-Id`, contains the `openId` which is assigned to all recordings in this
live stream.
Initiate a WebSocket stream for chunks of video. Expects the standard
WebSocket headers as described in [RFC 6455][rfc-6455] and (if authentication
is required) the `s` cookie.
Each part is a `.mp4` media segment that starts with a key frame and contains
all other frames which depend on that key frame. The following part headers
will be included:
The server will send a sequence of binary messages. Each message corresponds
to one run (GOP) of video: a key (IDR) frame and all other frames which depend
on it. These are encoded as a `.mp4` media segment. The following headers will
be included:
* `Content-Length`: as defined by HTTP
* `Content-Type`: the MIME type, including `codecs` parameter.
* `X-Recording-Id`: the ID of the recording these frames are contained in.
* `X-Recording-Id`: the open id, a period, and the recording id of the
recording these frames belong to.
* `X-Recording-Start`: the timestamp (in Moonfire NVR's usual 90,000ths
of a second) of the start of the recording. Note that if the recording
is "unanchored" (as described in `GET /api/.../recordings`), the
recording's start time may change before it is completed.
* `X-Time-Range`: the relative start and end times of these frames within
the recording, in the same format as `REL_START_TIME` and `REL_END_TIME`
above.
@@ -442,40 +446,36 @@ Example request URI:
/api/cameras/fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe/main/live.m4s
```
Example response:
Example binary message sequence:
```
Content-Type: multipart/mixed; boundary=B
X-Open-Id: 42
--B
Content-Length: 536445
Content-Type: video/mp4; codecs="avc1.640028"
X-Recording-Id: 5680
X-Recording-Id: 42.5680
X-Recording-Start: 130985461191810
X-Time-Range: 5220058-5400061
X-Video-Sample-Entry-Sha1: 25fad1b92c344dadc0473a783dff957b0d7d56bb
binary mp4 data
```
--B
Content-Length: 541118
```
Content-Type: video/mp4; codecs="avc1.640028"
X-Recording-Id: 5681
X-Recording-Id: 42.5681
X-Recording-Start: 130985461191822
X-Time-Range: 0-180002
X-Video-Sample-Entry-Sha1: 25fad1b92c344dadc0473a783dff957b0d7d56bb
binary mp4 data
```
--B
Content-Length: 539195
```
Content-Type: video/mp4; codecs="avc1.640028"
X-Recording-Id: 5681
X-Recording-Id: 42.5681
X-Recording-Start: 130985461191822
X-Time-Range: 180002-360004
X-Video-Sample-Entry-Sha1: 25fad1b92c344dadc0473a783dff957b0d7d56bb
binary mp4 data
...
```
These segments are exactly the same as ones that can be retrieved at the
@@ -485,6 +485,13 @@ following URLs, respectively:
* `/api/cameras/fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe/main/view.m4s?s=5681@42.0-180002`
* `/api/cameras/fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe/main/view.m4s?s=5681@42.180002-360004`
Note: an earlier version of this API used a `multipart/mixed` segment instead,
compatible with the [multipart-stream-js][multipart-stream-js] library. The
problem with this approach is that browsers have low limits on the number of
active HTTP/1.1 connections: six in Chrome's case. The WebSocket limit is much
higher (256), allowing browser-side Javascript to stream all active camera
streams simultaneously as well as making other simultaneous HTTP requests.
### `GET /api/init/<sha1>.mp4`
Returns a `.mp4` suitable for use as a [HTML5 Media Source Extensions
@@ -660,3 +667,5 @@ Response:
[media-segment]: https://w3c.github.io/media-source/isobmff-byte-stream-format.html#iso-media-segments
[init-segment]: https://w3c.github.io/media-source/isobmff-byte-stream-format.html#iso-init-segments
[rfc-6381]: https://tools.ietf.org/html/rfc6381
[rfc-6455]: https://tools.ietf.org/html/rfc6455
[multipart-mixed-js]: https://github.com/scottlamb/multipart-mixed-js