moonfire-nvr/design/api.md

Moonfire NVR API

Status: unstable. This is an early draft; the API may change without warning.

Objective

Allow a JavaScript-based web interface to list cameras and view recordings.

In the future, this is likely to be expanded:

• configuration support
• commandline tool over a UNIX-domain socket (at least for bootstrapping web authentication)
• mobile interface

Detailed design

All requests for JSON data should be sent with the header Accept: application/json (exactly). Without this header, replies will generally be in HTML rather than JSON.

TODO(slamb): authentication.

/cameras

A GET request on this URL returns basic information about all cameras. The application/json response will have a top-level cameras with a list of attributes about each camera:

• uuid: in text format
• short\_name: a short name (typically one or two words)
• description: a longer description (typically a phrase or paragraph)
• retain\_bytes: the configured total number of bytes of completed recordings to retain.
• min\_start\_time\_90k: the start time of the earliest recording for this camera, in 90kHz units since 1970-01-01 00:00:00 UTC.
• max\_end\_time\_90k: the end time of the latest recording for this camera, in 90kHz units since 1970-01-01 00:00:00 UTC.
• total\_duration\_90k: the total duration recorded, in 90 kHz units. This is no greater than max\_end\_time\_90k - max\_start\_time\_90k; it will be lesser if there are gaps in the recorded data.
• total\_sample\_file\_bytes: the total number of bytes of sample data (the mdat portion of a .mp4 file).

Example response:

{
  "cameras": [
    {
      "uuid": "fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe",
      "short_name": "driveway",
      "description": "Hikvision DS-2CD2032 overlooking the driveway from east",
      "retain_bytes": 536870912000,
      "min_start_time_90k": 130888729442361,
      "max_end_time_90k": 130985466591817
      "total_duration_90k": 96736169725,
      "total_sample_file_bytes": 446774393937,
    },
    ...
  ],
}

/cameras/<uuid>

A GET returns information for the camera with the given URL. The information returned is a superset of that returned by the camera list. It also includes a list of calendar days (in the server's time zone) with data in the server's time zone. The days entry is a object mapping YYYY-mm-dd to a day object with the following attributes:

• total_duration_90k is the total duration recorded during that day. If a recording spans a day boundary, some portion of it is accounted to each day.
• start_time_90k is the start of that calendar day in the server's time zone.
• end_time_90k is the end of that calendar day in the server's time zone. It is usually 24 hours after the start time. It might be 23 hours or 25 hours during spring forward or fall back, respectively.

A calendar day will be present in the days object iff there is a non-zero total duration of recordings for that day.

Example response:

{
  "days": {
    "2016-05-01": {
      "end_time_usec": 131595516000000,
      "start_time_usec": 131587740000000,
      "total_duration_90k": 52617609
    },
    "2016-05-02": {
      "end_time_usec": 131603292000000,
      "start_time_usec": 131595516000000,
      "total_duration_90k": 20946022
    }
  },
  "description":"",
  "max_end_time_90k": 131598273666690,
  "min_start_time_90k": 131590386129355,
  "retain_bytes": 104857600,
  "short_name": "driveway",
  "total_duration_90k": 73563631,
  "total_sample_file_bytes": 98901406,
}

/camera/<uuid>/recordings

A GET returns information about recordings, in descending order.

TODO(slamb): once we support annotations, should they be included in the same URI or as a separate /annotations?

TODO(slamb): this should support paging. The client can limit the range via the URI parameters start\_time\_90k and end\_time\_90k. If the range is too large, the server will return some fraction of the data along with a continuation key to pass in for the next request.

TODO(slamb): There might be some irregularity in the order if there are overlapping recordings (such as if the server's clock jumped while running) but I haven't thought about the details. In general, I'm not really sure how to handle this case, other than ideally to keep recording stuff no matter what and present some UI to help the user to fix it after the fact.

In the property recordings, returns a list of recordings. Each recording object has the following properties:

• start\_time\_90k
• end\_time\_90k
• sample\_file\_bytes
• video\_sample\_entry\_sha1
• video\_sample\_entry\_width
• video\_sample\_entry\_height

TODO(slamb): consider ways to reduce the data size; this is in theory quite compressible but I'm not sure how effective gzip will be without some tweaks. One simple approach would be to just combine some adjacent list entries if one's start matches the other's end exactly and the video\_sample\_entry\_* parameters are the same. So you might get one entry that represents 2 hours of video instead of 120 entries representing a minute each.

Example request URI (with added whitespace between parameters):

/camera/fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe/recordings
    ?start_time_90k=130888729442361
    &end_time_90k=130985466591817

Example response:

{
  "recordings": [
    {
      "end_time_90k": 130985466591817,
      "start_time_90k": 130985461191810,
      "sample_file_bytes": 8405564,
      "video_sample_entry_sha1": "81710c9c51a02cc95439caa8dd3bc12b77ffe767",
      "video_sample_entry_width": 1280,
      "video_sample_entry_height": 720,
    },
    {
      "end_time_90k": 130985461191810,
      ...
    },
    ...
  ],
  "continuation_key": "<opaque blob>",
}

/camera/<uuid>/view.mp4

A GET returns a .mp4 file, with an etag and support for range requests.

Expected query parameters:

• start\_time\_90k
• end\_time\_90k
• ts: should be set to true to request a subtitle track be added with human-readable recording timestamps.
• TODO(slamb): possibly overlap to indicate what to do about segments of recording with overlapping wall times. Values might include:
  • error (return an HTTP error)
  • include_all (include all, in order of the recording ids)
  • include_latest (include only the latest by recording id for a particular segment of time)
• TODO(slamb): gaps allowed or not? maybe a parameter for this also?