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_90k": 131595516000000,
      "start_time_90k": 131587740000000,
      "total_duration_90k": 52617609
    },
    "2016-05-02": {
      "end_time_90k": 131603292000000,
      "start_time_90k": 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.

Valid request parameters:

• start_time_90k and and end_time_90k limit the data returned to only recordings which overlap with the given half-open interval. Either or both may be absent; they default to the beginning and end of time, respectively.
• TODO(slamb): continue to support paging. (If data is too large, the server should return a continue key which is expected to be returned on following requests.)

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

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

• start_id. The id of this recording, which can be used with /view.mp4 to retrieve its content.
• end_id (optional). If absent, this object describes a single recording. If present, this indicates that recordings start_id-end_id (inclusive) together are as described. Adjacent recordings from the same RTSP session may be coalesced in this fashion to reduce the amount of redundant data transferred.
• start_time_90k: the start time of the given recording. Note this may be less than the requested start_time_90k if this recording was ongoing at the requested time.
• end_time_90k: the end time of the given recording. Note this may be greater than the requested end_time_90k if this recording was ongoing at the requested time.
• sample_file_bytes
• video_sample_entry_sha1
• video_sample_entry_width
• video_sample_entry_height
• video_samples: the number of samples (aka frames) of video in this recording.

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": [
    {
      "start_id": 1,
      "start_time_90k": 130985461191810,
      "end_time_90k": 130985466591817,
      "sample_file_bytes": 8405564,
      "video_sample_entry_sha1": "81710c9c51a02cc95439caa8dd3bc12b77ffe767",
      "video_sample_entry_width": 1280,
      "video_sample_entry_height": 720,
    },
    {
      "end_time_90k": 130985461191810,
      ...
    },
    ...
  ],
  "continue": "<opaque blob>",
}

/camera/<uuid>/view.mp4

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

Expected query parameters:

• s (one or more): a string of the form START_ID[-END_ID][.[REL_START_TIME]-[REL_END_TIME]]. This specifies recording segments to include. The produced .mp4 file will be a concatenation of the segments indicated by all s parameters. The ids to retrieve are as returned by the /recordings URL. The optional start and end times are in 90k units and relative to the start of the first specified id. These can be used to clip the returned segments. Note they can be used to skip over some ids entirely; this is allowed so that the caller doesn't need to know the start time of each interior id. If there is no key frame at the desired relative start time, frames back to the last key frame will be included in the returned data, and an edit list will instruct the viewer to skip to the desired start time.
• ts (optional): should be set to true to request a subtitle track be added with human-readable recording timestamps.

Example request URI to retrieve all of recording id 1 from the given camera:

    /camera/fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe/view.mp4?s=1

Example request URI to retrieve all of recording ids 1–5 from the given camera, with timestamp subtitles:

    /camera/fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe/view.mp4?s=1-5&ts=true

Example request URI to retrieve recording id 1, skipping its first 26 90,000ths of a second:

    /camera/fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe/view.mp4?s=1.26

TODO: error behavior on missing segment. It should be a 404, likely with an application/json body describing what portion if any (still) exists.

/camera/<uuid>/view.m4s

A GET returns a .mp4 suitable for use as a HTML5 Media Source Extensions media segment.

Expected query parameters:

• s (one or more): as with the .mp4 URL, except that media segments can't contain edit lists so none will be generated. TODO: maybe add a Leading-Time: header to indicate how many leading 90,000ths of a second are present, so that the caller can trim it in some other way.

It's recommended that each .m4s retrieval be for at most one Moonfire NVR recording segment for several reasons:

• The Media Source Extension API appears structured for adding a complete segment at a time. Large media segments thus impose significant latency on seeking.
• There is currently a hard limit of 4 GiB of data because the .m4s uses a single moof followed by a single mdat; the former references the latter with 32-bit offsets.
• There's currently no way to generate an initialization segment for more than one video sample entry, so a .m4s that uses more than one video sample entry can't be used.

/init/<sha1>.mp4

A GET returns a .mp4 suitable for use as a HTML5 Media Source Extensions initialization segment.

TODO: return a MIME type with a Codecs parameter as in RFC 6381. Web browsers expect this parameter when initializing a SourceBuffer; currently the user agent must divine this information.