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moonfire-nvr/design/api.md
Scott Lamb 30d5807dd3 include ids in api responses for debugging
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Moonfire NVR API

Status: current.

Objective

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

In the future, this is likely to be expanded:

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

Detailed design

Note: italicized terms in this document are defined in the glossary.

All requests for JSON data should be sent with the header Accept: application/json (exactly).

POST /api/login

The request should have an application/json body containing a dict with username and password keys.

On successful authentication, the server will return an HTTP 204 (no content) with a Set-Cookie header for the s cookie, which is an opaque, HttpOnly (unavailable to Javascript) session identifier.

If authentication or authorization fails, the server will return a HTTP 403 (forbidden) response. Currently the body will be a text/plain error message; future versions will likely be more sophisticated.

POST /api/logout

The request should have an application/json body containing a csrf parameter copied from the session.csrf of the top-level API request.

On success, returns an HTTP 204 (no content) responses. On failure, returns a 4xx response with text/plain error message.

GET /api/

Returns basic information about the server, including all cameras. Valid request parameters:

  • days: a boolean indicating if the days parameter described below should be included.
  • cameraConfigs: a boolean indicating if the camera.config and camera.stream[].config parameters described below should be included. This requires the read_camera_configs permission as described in schema.proto.

Example request URI (with added whitespace between parameters):

/api/?days=true
     &cameraConfigs=true

The application/json response will have a dict as follows:

  • timeZoneName: the name of the IANA time zone the server is using to divide recordings into days as described further below.
  • cameras: a list of cameras. Each is a dict as follows:
    • uuid: in text format
    • id: an integer. The client doesn't ever need to send the id back in API requests, but camera ids are helpful to know when debugging by reading logs or directly examining the filesystem/database.
    • shortName: a short name (typically one or two words)
    • description: a longer description (typically a phrase or paragraph)
    • config: (only included if request parameter cameraConfigs is true) a dictionary describing the configuration of the camera:
      • username
      • password
      • onvif_host
    • streams: a dict of stream type ("main" or "sub") to a dictionary describing the stream:
      • id: an integer. The client doesn't ever need to send the id back in API requests, but stream ids are helpful to know when debugging by reading logs or directly examining the filesystem/database.
      • retainBytes: the configured total number of bytes of completed recordings to retain.
      • minStartTime90k: the start time of the earliest recording for this camera, in 90kHz units since 1970-01-01 00:00:00 UTC.
      • maxEndTime90k: the end time of the latest recording for this camera, in 90kHz units since 1970-01-01 00:00:00 UTC.
      • totalDuration90k: the total duration recorded, in 90 kHz units. This is no greater than maxEndTime90k - maxStartTime90k; it will be lesser if there are gaps in the recorded data.
      • totalSampleFileBytes: the total number of bytes of sample data (the mdat portion of a .mp4 file).
      • fsBytes: the total number of bytes on the filesystem used by this stream. This is slightly more than totalSampleFileBytes because it also includes the wasted portion of the final filesystem block allocated to each file.
      • days: (only included if request parameter days is true) dictionary representing calendar days (in the server's time zone) with non-zero total duration of recordings for that day. Currently this includes uncommitted and growing recordings. This is likely to change in a future release for #40. The keys are of the form YYYY-mm-dd; the values are objects with the following attributes:
        • totalDuration90k is the total duration recorded during that day. If a recording spans a day boundary, some portion of it is accounted to each day.
        • startTime90k is the start of that calendar day in the server's time zone.
        • endTime90k 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.
      • config: (only included if request parameter cameraConfigs is true) a dictionary describing the configuration of the stream:
        • rtsp_url
  • signals: a list of all signals known to the server. Each is a dictionary with the following properties:
    • id: an integer identifier.
    • shortName: a unique, human-readable description of the signal
    • cameras: a map of associated cameras' UUIDs to the type of association: direct or indirect. See db/schema.sql for more description.
    • type: a UUID, expected to match one of signalTypes.
    • days: (only included if request parameter days is true) similar to cameras.days above. Values are objects with the following attributes:
      • states: an array of the time the signal is in each state, starting from 1. These may not sum to the entire day; if so, the rest of the day is in state 0 (unknown).
  • signalTypes: a list of all known signal types.
    • uuid: in text format.
    • states: a map of all possible states of the enumeration to more information about them:
      • color: a recommended color to use in UIs to represent this state, as in the HTML specification.
      • motion: if present and true, directly associated cameras will be considered to have motion when this signal is in this state.
  • session: if logged in, a dict with the following properties:
    • username
    • csrf: a cross-site request forgery token for use in POST requests.

Example response:

{
  "timeZoneName": "America/Los_Angeles",
  "cameras": [
    {
      "uuid": "fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe",
      "shortName": "driveway",
      "description": "Hikvision DS-2CD2032 overlooking the driveway from east",
      "config": {
        "onvif_host": "192.168.1.100",
        "user": "admin",
        "password": "12345",
      },
      "streams": {
        "main": {
          "retainBytes": 536870912000,
          "minStartTime90k": 130888729442361,
          "maxEndTime90k": 130985466591817,
          "totalDuration90k": 96736169725,
          "totalSampleFileBytes": 446774393937,
          "record": true,
          "days": {
            "2016-05-01": {
              "endTime90k": 131595516000000,
              "startTime90k": 131587740000000,
              "totalDuration90k": 52617609
            },
            "2016-05-02": {
              "endTime90k": 131603292000000,
              "startTime90k": 131595516000000,
              "totalDuration90k": 20946022
            }
          }
        }
      }
    },
    ...
  ],
  "signals": [
    {
      "id": 1,
      "shortName": "driveway motion",
      "cameras": {
        "fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe": "direct"
      },
      "type": "ee66270f-d9c6-4819-8b33-9720d4cbca6b",
      "days": {
        "2016-05-01": {
           "endTime90k": 131595516000000,
           "startTime90k": 131587740000000,
           "states": [5400000]
         }
       }
    }
  ],
  "signalTypes": [
    {
      "uuid": "ee66270f-d9c6-4819-8b33-9720d4cbca6b",
      "states": {
        0: {
          "name": "unknown",
          "color": "#000000"
        },
        1: {
          "name": "off",
          "color": "#888888"
        },
        2: {
          "name": "on",
          "color": "#ff8888",
          "motion": true
        }
      }
    }
  ],
  "session": {
    "username": "slamb",
    "csrf": "2DivvlnKUQ9JD4ao6YACBJm8XK4bFmOc"
  }
}

GET /api/cameras/<uuid>/

Returns information for the camera with the given URL. As in the like section of GET /api/ with the days parameter set and the cameraConfigs parameter unset.

Example response:

{
  "description": "",
  "streams": {
    "main": {
      "days": {
        "2016-05-01": {
          "endTime90k": 131595516000000,
          "startTime90k": 131587740000000,
          "totalDuration90k": 52617609
        },
        "2016-05-02": {
          "endTime90k": 131603292000000,
          "startTime90k": 131595516000000,
          "totalDuration90k": 20946022
        }
      },
      "maxEndTime90k": 131598273666690,
      "minStartTime90k": 131590386129355,
      "retainBytes": 104857600,
      "totalDuration90k": 73563631,
      "totalSampleFileBytes": 98901406
    }
  },
  "shortName": "driveway"
}

GET /api/cameras/<uuid>/<stream>/recordings

Returns information about recordings. Valid request parameters:

  • startTime90k and and endTime90k limit the data returned to only recordings with wall times overlapping with the given half-open interval. Either or both may be absent; they default to the beginning and end of time, respectively.
  • split90k causes long runs of recordings to be split at the next convenient boundary after the given duration.
  • 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.)

Returns a JSON object. Under the key recordings is an array of recordings in arbitrary order. Each recording object has the following properties:

  • startId. The id of this recording, which can be used with /view.mp4 to retrieve its content.
  • endId (optional). If absent, this object describes a single recording. If present, this indicates that recordings startId-endId (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.
  • firstUncommitted (optional). If this range is not fully committed to the database, the first id that is uncommitted. This is significant because it's possible that after a crash and restart, this id will refer to a completely different recording. That recording will have a different openId.
  • growing (optional). If this boolean is true, the recording endId is still being written to. Accesses to this id (such as view.mp4) may retrieve more data than described here if not bounded by duration. Additionally, if startId == endId, the start time of the recording is "unanchored" and may change in subsequent accesses.
  • openId. Each time Moonfire NVR starts in read-write mode, it is assigned an increasing "open id". This field is the open id as of when these recordings were written. This can be used to disambiguate ids referring to uncommitted recordings.
  • startTime90k: the start time of the given recording, in the wall time scale. Note this may be less than the requested startTime90k if this recording was ongoing at the requested time.
  • endTime90k: the end time of the given recording, in the wall time scale. Note this may be greater than the requested endTime90k if this recording was ongoing at the requested time.
  • videoSampleEntryId: a reference to an entry in the videoSampleEntries object.
  • videoSamples: the number of samples (aka frames) of video in this recording.
  • sampleFileBytes: the number of bytes of video in this recording.

Under the property videoSampleEntries, an object mapping ids to objects with the following properties:

  • width: the stored width in pixels.
  • height: the stored height in pixels.
  • pixelHSpacing: the relative width of a pixel, as in a ISO/IEC 14496-12 section 12.1.4.3 PixelAspectRatioBox. If absent, assumed to be 1.
  • pixelVSpacing: the relative height of a pixel, as in a ISO/IEC 14496-12 section 12.1.4.3 PixelAspectRatioBox. If absent, assumed to be 1.
  • aspectWidth: the width component of the aspect ratio. (The aspect ratio can be computed from the dimensions and pixel spacing; it's included as a convenience.)
  • aspectHeight: the height component of the aspect ratio.

The full initialization segment data for a given video sample entry can be retrieved at the URL /api/init/<id>.mp4.

Example request URI (with added whitespace between parameters):

/api/cameras/fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe/main/recordings
    ?startTime90k=130888729442361
    &endTime90k=130985466591817

Example response:

{
  "recordings": [
    {
      "startId": 1,
      "startTime90k": 130985461191810,
      "endTime90k": 130985466591817,
      "sampleFileBytes": 8405564,
      "videoSampleEntryId": 1,
    },
    {
      "endTime90k": 130985461191810,
      ...
    },
    ...
  ],
  "videoSampleEntries": {
    "1": {
      "width": 1280,
      "height": 720
    }
  },
}

GET /api/cameras/<uuid>/<stream>/view.mp4

Requires the view_video permission.

Returns a .mp4 file, with an etag and support for range requests. The MIME type will be video/mp4, with a codecs parameter as specified in RFC 6381.

Expected query parameters:

  • s (one or more): a string of the form START_ID[-END_ID][@OPEN_ID][.[REL_START_TIME]-[REL_END_TIME]]. This specifies 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 open id is optional and will be enforced if present; it's recommended for disambiguation when the requested range includes uncommitted recordings. The optional start and end times are in 90k units of wall time 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:

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

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

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

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

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

Note carefully the distinction between wall duration and media duration. It's normal for /view.mp4 to return a media presentation with a length slightly different from the wall duration of the backing recording or portion that was requested.

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

GET /api/cameras/<uuid>/<stream>/view.mp4.txt

Returns a text/plain debugging string for the .mp4 generated by the same URL minus the .txt suffix.

GET /api/cameras/<uuid>/<stream>/view.m4s

Returns a .mp4 suitable for use as a HTML5 Media Source Extensions media segment. The MIME type will be video/mp4, with a codecs parameter as specified in RFC 6381. Note that these can't include edit lists, so (unlike /view.mp4) the caller must manually trim undesired leading portions.

This response will include the following additional headers:

  • X-Prev-Media-Duration: the total media duration (in 90 kHz units) of all recordings before the first requested recording in the s parameter. Browser-based callers may use this to place this at the correct position in the source buffer via SourceBuffer.timestampOffset.
  • X-Runs: the cumulative number of "runs" of recordings. If this recording starts a new run, it is included in the count. Browser-based callers may use this to force gaps in the source buffer timeline by adjusting the timestamp offset if desired.
  • X-Leading-Media-Duration: if present, the total duration (in 90 kHz units) of additional leading video included before the caller's first requested timestamp. This happens when the caller's requested timestamp does not fall exactly on a key frame. Media segments can't include edit lists, so unlike with the /api/.../view.mp4 endpoint the caller is responsible for trimming this portion. Browser-based callers may use SourceBuffer.appendWindowStart.

Expected query parameters:

  • s (one or more): as with the .mp4 URL.

It's recommended that each .m4s retrieval be for at most one Moonfire NVR recording segment. The fundamental reason is that the Media Source Extension API appears structured for adding a complete segment at a time. Large media segments thus impose significant latency on seeking. Additionally, because of this fundamental reason Moonfire NVR makes no effort to make multiple-segment .m4s requests practical:

  • 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.
  • The X-Prev-Media-Duration and X-Leading-Media-Duration headers only describe the first segment.

Timestamp tracks (see the ts parameter to .mp4 URIs) aren't supported today. Most likely browser clients will implement timestamp subtitles via WebVTT API calls anyway.

GET /api/cameras/<uuid>/<stream>/view.m4s.txt

Returns a text/plain debugging string for the .mp4 generated by the same URL minus the .txt suffix.

GET /api/cameras/<uuid>/<stream>/live.m4s

Initiate a WebSocket stream for chunks of video. Expects the standard WebSocket headers as described in RFC 6455 and (if authentication is required) the s cookie.

The server will send a sequence of binary messages. Each message corresponds to one or more frames of video. The first message is guaranteed to start with a "key" (IDR) frame; others may not. The message will contain HTTP headers followed by by a .mp4 media segment. The following headers will be included:

  • 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-Prev-Media-Duration: as in /.../view.m4s.
  • X-Runs: as in /.../view.m4s.
  • X-Media-Time-Range: the relative media start and end times of these frames within the recording, as a half-open interval.

The server will also send pings, currently at 30-second intervals.

The WebSocket will always open immediately but will receive messages only while the backing RTSP stream is connected.

Example request URI:

/api/cameras/fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe/main/live.m4s

Example binary message sequence:

Content-Type: video/mp4; codecs="avc1.640028"
X-Recording-Id: 42.5680
X-Recording-Start: 130985461191810
X-Prev-Media-Duration: 10000000
X-Media-Time-Range: 5220058-5400061
X-Video-Sample-Entry-Id: 4

binary mp4 data

Content-Type: video/mp4; codecs="avc1.640028"
X-Recording-Id: 42.5681
X-Recording-Start: 130985461191822
X-Prev-Media-Duration: 10180003
X-Media-Time-Range: 0-180002
X-Video-Sample-Entry-Id: 4

binary mp4 data

Content-Type: video/mp4; codecs="avc1.640028"
X-Recording-Id: 42.5681
X-Recording-Start: 130985461191822
X-Prev-Media-Duration: 10360005
X-Media-Time-Range: 180002-360004
X-Video-Sample-Entry-Id: 4

binary mp4 data

These roughly correspond to the .m4s files available at the following URLs:

  • /api/cameras/fd20f7a2-9d69-4cb3-94ed-d51a20c3edfe/main/view.m4s?s=5680@42.5220058-5400061
  • /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

However, there are two important differences:

  • The /view.m4s endpoint accepts offsets within a recording as wall durations; the /live.m4s endpoint's X-Media-Time-Range header returns them as media durations. Thus the URLs above are only exactly correct if the wall and media durations of the recording are identical.
  • The /view.m4s endpoint always returns a time range that starts with a key frame; /live.m4s messages may not include a key frame.

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/<id>.mp4

Returns a .mp4 suitable for use as a HTML5 Media Source Extensions initialization segment. The MIME type will be video/mp4, with a codecs parameter as specified in RFC 6381.

An X-Aspect HTTP header will include the aspect ratio as width:height, eg 16:9 (most cameras) or 9:16 (rotated 90 degrees). This is redundant with the returned .mp4 but is far easier to parse from Javascript.

GET /api/init/<id>.mp4.txt

Returns a text/plain debugging string for the .mp4 generated by the same URL minus the .txt suffix.

GET /api/signals

Returns an application/json response with state of every signal for the requested timespan.

Valid request parameters:

  • startTime90k and and endTime90k limit the data returned to only events relevant to the given half-open interval. Either or both may be absent; they default to the beginning and end of time, respectively. This will return the current state as of the latest change (to any signal) before the start time (if any), then all changes in the interval. This allows the caller to determine the state at every moment during the selected timespan, as well as observe all events.

Responses are several parallel arrays for each observation:

  • times90k: the time of each event. Events are given in ascending order.
  • signalIds: the id of the relevant signal; expected to match one in the signals field of the /api/ response.
  • states: the new state.

Example request URI (with added whitespace between parameters):

/api/signals
    ?startTime90k=130888729442361
    &endTime90k=130985466591817

Example response:

{
  "signalIds": [1, 1, 1],
  "states": [1, 2, 1],
  "times90k": [130888729440000, 130985424000000, 130985418600000]
}

This represents the following observations:

  1. time 130888729440000 was the last change before the requested start; signal 1 (driveway motion) was in state 1 (off).
  2. signal 1 entered state 2 (on) at time 130985424000000.
  3. signal 1 entered state 1 (off) at time 130985418600000.

POST /api/signals

Requires the update_signals permission.

Alters the state of a signal.

A typical client might be a subscriber of a camera's built-in motion detection event stream or of a security system's zone status event stream. It makes a request on every event or on every 30 second timeout, predicting that the state will last for a minute. This prediction may be changed later. Writing to the near future in this way ensures that the UI never displays unknown when the client is actively managing the signal.

Some requests may instead backfill earlier history, such as when a video analytics client starts up and analyzes all video segments recorded since it last ran. These will specify beginning and end times.

The request should have an application/json body describing the change to make. It should be a dict with these attributes:

  • signalIds: a list of signal ids to change. Must be sorted.
  • states: a list (one per signalIds entry) of states to set.
  • start: the starting time of the change, as a dict of the form {'base': 'epoch', 'rel90k': t} or {'base': 'now', 'rel90k': t}. In the epoch form, rel90k is 90 kHz units since 1970-01-01 00:00:00 UTC. In the now form, rel90k is relative to current time and may be negative.
  • end: the ending time of the change, in the same form as start.

The response will be an application/json body dict with the following attributes:

  • time90k: the current time. When the request's startTime90k is absent and/or its endBase is now, this is needed to know the effect of the earlier request.

Example request sequence:

Request 1

The client responsible for reporting live driveway motion has just started. It observes motion now. It records no history and predicts there will be motion for the next minute.

Request:

{
  "signalIds": [1],
  "states": [2],
  "start": {"base": "now", "rel90k": 0},
  "end": {"base": "now", "rel90k": 5400000}
}

Response:

{
  "time90k": 140067468000000
}

Request 2

30 seconds later (half the prediction interval), the client still observes motion. It leaves the prior data alone and predicts the motion will continue.

Request:

{
  "signalIds": [1],
  "states": [2],
  "start": {"base": "epoch", "rel90k": 140067468000000},
  "end": {"base": "now", "rel90k": 5400000}
}

Response:

{
  "time90k": 140067470700000
}

Request 3

5 seconds later, the client observes motion has ended. It leaves the prior data alone and predicts no more motion.

Request:

{
  "signalIds": [1],
  "states": [2],
  "start": {"base": "now", "rel90k": 0},
  "end": {"base": "now", "rel90k": 5400000}
  }
}

Response:

{
  "time90k": 140067471150000
}