Export Jellyfin playback statistics to Prometheus and Grafana. See https://sno.ws/jellyfin-stats for more info

json-exporter-config.yaml

modules:
  jellyfin:
    headers:
      # The Token value here needs to be an API key generated from the
      # Jellyfin admin panel. It's hard-coded here but I'm sure there's
      # a better way
      Authorization: MediaBrowser Token=ADD_TOKEN_HERE
      Content-Type: application/json
      accept: application/json

    # This will return all active sessions regardless of
    # whether something is playing. You can use a combination
    # of label and value filters in Grafana to only get actively
    # playing sessions
    metrics:
    - name: jellyfin
      type: object
      help: User playback metrics from Jellyfin
      # Only look at sessions with a NowPlayingItem key, per @abe-kanofsky
      path: '{ [?(@.NowPlayingItem)] }'
      labels:
        user_name: '{ .UserName }'
        # User PromQL label_join and label_replace to concatenate
        # these values into a nice item description
        item_type: '{ .NowPlayingItem.Type }'
        item_name: '{ .NowPlayingItem.Name }'
        item_path: '{ .NowPlayingItem.Path }'
        series_name: '{ .NowPlayingItem.SeriesName }'
        episode_index: 'e{ .NowPlayingItem.IndexNumber }'
        season_index: 's{ .NowPlayingItem.ParentIndexNumber }'
        client_name: '{ .Client }'
        device_name: '{ .DeviceName }'
        # Include the unique session ID in case the above info isn't unique
        session_id: '{ .Id }'
      values:
        is_paused: '{ .PlayState.IsPaused }'

prometheus-config.yaml

scrape_configs:
  - job_name: json
    metrics_path: /probe
    params:
      # The name of the module defined by json-exporter-config.yaml
      module: [jellyfin] 
    static_configs:
      - targets:
        # Use the Sessions endpoint to see actively playing items
        - https://jellyfin.example.com/Sessions
    relabel_configs:
      - source_labels: [__address__]
        target_label: __param_target
      - source_labels: [__param_target]
        target_label: instance
      - target_label: __address__
        replacement: HOSTNAME:9115 # The exporter's hostname:port

state-timeline-grafana-panel.json

{
  "datasource": {
    "type": "prometheus",
    "uid": "D5GQA944k"
  },
  "description": "",
  "fieldConfig": {
    "defaults": {
      "custom": {
        "lineWidth": 0,
        "fillOpacity": 70,
        "spanNulls": false,
        "insertNulls": false,
        "hideFrom": {
          "tooltip": false,
          "viz": false,
          "legend": false
        }
      },
      "color": {
        "mode": "continuous-GrYlRd"
      },
      "mappings": [],
      "thresholds": {
        "mode": "absolute",
        "steps": [
          {
            "color": "green",
            "value": null
          },
          {
            "color": "red",
            "value": 80
          }
        ]
      }
    },
    "overrides": []
  },
  "gridPos": {
    "h": 6,
    "w": 13,
    "x": 0,
    "y": 9
  },
  "id": 348,
  "options": {
    "mergeValues": true,
    "showValue": "auto",
    "alignValue": "left",
    "rowHeight": 0.9,
    "legend": {
      "showLegend": true,
      "displayMode": "list",
      "placement": "bottom"
    },
    "tooltip": {
      "mode": "single",
      "sort": "none"
    }
  },
  "pluginVersion": "10.1.1",
  "targets": [
    {
      "datasource": {
        "type": "prometheus",
        "uid": "D5GQA944k"
      },
      "editorMode": "code",
      "expr": "sum by (user_name, item_index_clean, item_type) (label_replace(label_join(label_join(jellyfin_is_paused{job=\"json\"}, \"item_index\", \"\", \"season_index\", \"episode_index\"), \"full_name\", \" - \", \"series_name\", \"item_index\", \"item_name\"), \"item_index_clean\", \"$1\", \"full_name\", \"^[- ]*(.*?)[- ]*$\"))",
      "instant": false,
      "legendFormat": "__auto",
      "range": true,
      "refId": "A"
    }
  ],
  "title": "Jellyfin",
  "transformations": [
    {
      "id": "seriesToRows",
      "options": {}
    },
    {
      "id": "extractFields",
      "options": {
        "keepTime": false,
        "replace": false,
        "source": "Metric"
      }
    },
    {
      "id": "filterByValue",
      "options": {
        "filters": [
          {
            "config": {
              "id": "isNotNull",
              "options": {}
            },
            "fieldName": "user_name"
          }
        ],
        "match": "any",
        "type": "include"
      }
    },
    {
      "id": "calculateField",
      "options": {
        "alias": "Item",
        "mode": "reduceRow",
        "reduce": {
          "include": [
            "item_index_clean"
          ],
          "reducer": "firstNotNull"
        }
      }
    },
    {
      "id": "calculateField",
      "options": {
        "alias": "Name",
        "mode": "reduceRow",
        "reduce": {
          "include": [
            "user_name"
          ],
          "reducer": "firstNotNull"
        }
      }
    },
    {
      "id": "calculateField",
      "options": {
        "alias": "Temp",
        "mode": "reduceRow",
        "reduce": {
          "include": [
            "Item"
          ],
          "reducer": "firstNotNull"
        },
        "replaceFields": false
      }
    },
    {
      "id": "filterByValue",
      "options": {
        "filters": [
          {
            "config": {
              "id": "regex",
              "options": {
                "value": "(Movie|Episode)"
              }
            },
            "fieldName": "item_type"
          }
        ],
        "match": "any",
        "type": "include"
      }
    },
    {
      "id": "filterByValue",
      "options": {
        "filters": [
          {
            "config": {
              "id": "notEqual",
              "options": {
                "value": 1
              }
            },
            "fieldName": "Value"
          }
        ],
        "match": "any",
        "type": "include"
      }
    },
    {
      "id": "partitionByValues",
      "options": {
        "fields": [
          "Name"
        ]
      }
    },
    {
      "id": "filterFieldsByName",
      "options": {
        "include": {
          "pattern": "Temp|Time (.*)"
        }
      }
    },
    {
      "id": "renameByRegex",
      "options": {
        "regex": "Temp (.*)",
        "renamePattern": "$1"
      }
    }
  ],
  "type": "state-timeline"
}

Another thing: modules.jellyfin.metrics[0].path should be '{ [?(@.NowPlayingItem)] } to look at only sessions that actually have a NowPlayingItem key. Otherwise, the exporter also tries to read sessions without that key and spits out a pretty verbose error each time it encounters one, causing the log file to blow up.

Nice @abe-kanofsky, these are excellent suggestions! I'll update the gist and blogpost to reflect them.