feat: video auto fit based on video stream size

src/utils/videoFit.test.ts

@@ -0,0 +1,251 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { describe, expect, test, vi } from "vitest";
+import {
+  LocalTrack,
+  type LocalTrackPublication,
+  type RemoteTrackPublication,
+  Track,
+} from "livekit-client";
+
+import { ObservableScope } from "../state/ObservableScope";
+import { videoFit$, videoSizeFromParticipant$ } from "./videoFit";
+import { constant } from "../state/Behavior";
+import {
+  flushPromises,
+  mockLocalParticipant,
+  mockRemoteParticipant,
+} from "./test";
+
+describe("videoFit$ defaults", () => {
+  test.each([
+    {
+      videoSize: { width: 1920, height: 1080 },
+      tileSize: undefined,
+    },
+    {
+      videoSize: { width: 1080, height: 1920 },
+      tileSize: undefined,
+    },
+    {
+      videoSize: undefined,
+      tileSize: { width: 1920, height: 1080 },
+    },
+    {
+      videoSize: undefined,
+      tileSize: { width: 1080, height: 1920 },
+    },
+  ])(
+    "videoFit$ returns `cover` when videoSize is $videoSize and tileSize is $tileSize",
+    ({ videoSize, tileSize }) => {
+      const scope = new ObservableScope();
+      const videoSize$ = constant(videoSize);
+      const tileSize$ = constant(tileSize);
+
+      const fit = videoFit$(scope, videoSize$, tileSize$);
+      expect(fit.value).toBe("cover");
+    },
+  );
+});
+
+const VIDEO_480_L = { width: 640, height: 480 };
+const VIDEO_720_L = { width: 1280, height: 720 };
+const VIDEO_1080_L = { width: 1920, height: 1080 };
+
+// Some sizes from real world testing, which don't match the standard video sizes exactly
+const TILE_SIZE_1_L = { width: 180, height: 135 };
+const TILE_SIZE_3_P = { width: 379, height: 542 };
+const TILE_SIZE_4_L = { width: 957, height: 542 };
+// This is the size of an iPhone Xr in portrait mode
+const TILE_SIZE_5_P = { width: 414, height: 896 };
+
+export function invertSize(size: { width: number; height: number }): {
+  width: number;
+  height: number;
+} {
+  return {
+    width: size.height,
+    height: size.width,
+  };
+}
+
+test.each([
+  {
+    videoSize: VIDEO_480_L,
+    tileSize: TILE_SIZE_1_L,
+    expected: "cover",
+  },
+  {
+    videoSize: invertSize(VIDEO_480_L),
+    tileSize: TILE_SIZE_1_L,
+    expected: "contain",
+  },
+  {
+    videoSize: VIDEO_720_L,
+    tileSize: TILE_SIZE_4_L,
+    expected: "cover",
+  },
+  {
+    videoSize: invertSize(VIDEO_720_L),
+    tileSize: TILE_SIZE_4_L,
+    expected: "contain",
+  },
+  {
+    videoSize: invertSize(VIDEO_1080_L),
+    tileSize: TILE_SIZE_3_P,
+    expected: "cover",
+  },
+  {
+    videoSize: VIDEO_1080_L,
+    tileSize: TILE_SIZE_5_P,
+    expected: "contain",
+  },
+  {
+    videoSize: invertSize(VIDEO_1080_L),
+    tileSize: TILE_SIZE_5_P,
+    expected: "cover",
+  },
+  {
+    // square video
+    videoSize: { width: 400, height: 400 },
+    tileSize: VIDEO_480_L,
+    expected: "contain",
+  },
+])(
+  "videoFit$ returns $expected when videoSize is $videoSize and tileSize is $tileSize",
+  ({ videoSize, tileSize, expected }) => {
+    const scope = new ObservableScope();
+    const videoSize$ = constant(videoSize);
+    const tileSize$ = constant(tileSize);
+
+    const fit = videoFit$(scope, videoSize$, tileSize$);
+    expect(fit.value).toBe(expected);
+  },
+);
+
+describe("extracting video size from participant stats", () => {
+  function createMockRtpStats(
+    isInbound: boolean,
+    props: Partial<RTCInboundRtpStreamStats | RTCOutboundRtpStreamStats> = {},
+  ): RTCInboundRtpStreamStats | RTCOutboundRtpStreamStats {
+    const baseStats = {
+      id: "mock-stats-id",
+      timestamp: Date.now(),
+      type: isInbound ? "inbound-rtp" : "outbound-rtp",
+      kind: "video",
+      ...props,
+    };
+
+    return baseStats as RTCInboundRtpStreamStats | RTCOutboundRtpStreamStats;
+  }
+
+  test("get stats for local user", async () => {
+    const localParticipant = mockLocalParticipant({
+      identity: "@local:example.org:AAAAAA",
+    });
+
+    const mockReport: RTCStatsReport = new Map([
+      [
+        "OT01V639885149",
+        createMockRtpStats(false, {
+          frameWidth: 1280,
+          frameHeight: 720,
+        }),
+      ],
+    ]);
+
+    const track = {
+      source: Track.Source.Camera,
+      getRTCStatsReport: vi
+        .fn()
+        .mockImplementation(async () => Promise.resolve(mockReport)),
+    } as Partial<LocalTrack> as LocalTrack;
+
+    // Set up the prototype chain (there is an instanceof check in getRTCStatsReport)
+    Object.setPrototypeOf(track, LocalTrack.prototype);
+
+    localParticipant.getTrackPublication = vi
+      .fn()
+      .mockImplementation((source: Track.Source) => {
+        if (source === Track.Source.Camera) {
+          return {
+            track,
+          } as unknown as LocalTrackPublication;
+        } else {
+          return undefined;
+        }
+      });
+
+    const videoDimensions$ = videoSizeFromParticipant$(
+      constant(localParticipant),
+    );
+
+    const publishedDimensions: { width: number; height: number }[] = [];
+    videoDimensions$.subscribe((dimensions) => {
+      if (dimensions) publishedDimensions.push(dimensions);
+    });
+
+    await flushPromises();
+
+    const dimension = publishedDimensions.pop();
+    expect(dimension).toEqual({ width: 1280, height: 720 });
+  });
+
+  test("get stats for remote user", async () => {
+    // vi.useFakeTimers()
+    const remoteParticipant = mockRemoteParticipant({
+      identity: "@bob:example.org:AAAAAA",
+    });
+
+    const mockReport: RTCStatsReport = new Map([
+      [
+        "OT01V639885149",
+        createMockRtpStats(true, {
+          frameWidth: 480,
+          frameHeight: 640,
+        }),
+      ],
+    ]);
+
+    const track = {
+      source: Track.Source.Camera,
+      getRTCStatsReport: vi
+        .fn()
+        .mockImplementation(async () => Promise.resolve(mockReport)),
+    } as Partial<LocalTrack> as LocalTrack;
+
+    // Set up the prototype chain (there is an instanceof check in getRTCStatsReport)
+    Object.setPrototypeOf(track, LocalTrack.prototype);
+
+    remoteParticipant.getTrackPublication = vi
+      .fn()
+      .mockImplementation((source: Track.Source) => {
+        if (source === Track.Source.Camera) {
+          return {
+            track,
+          } as unknown as RemoteTrackPublication;
+        } else {
+          return undefined;
+        }
+      });
+
+    const videoDimensions$ = videoSizeFromParticipant$(
+      constant(remoteParticipant),
+    );
+
+    const publishedDimensions: { width: number; height: number }[] = [];
+    videoDimensions$.subscribe((dimensions) => {
+      if (dimensions) publishedDimensions.push(dimensions);
+    });
+
+    await flushPromises();
+
+    const dimension = publishedDimensions.pop();
+    expect(dimension).toEqual({ width: 480, height: 640 });
+  });
+});

src/utils/videoFit.ts

@@ -0,0 +1,94 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { combineLatest, map, type Observable, of, switchMap } from "rxjs";
+import {
+  type LocalParticipant,
+  type RemoteParticipant,
+  Track,
+} from "livekit-client";
+
+import { type ObservableScope } from "../state/ObservableScope.ts";
+import { type Behavior } from "../state/Behavior.ts";
+import {
+  observeInboundRtpStreamStats$,
+  observeOutboundRtpStreamStats$,
+} from "../state/MediaViewModel.ts";
+
+type Size = {
+  width: number;
+  height: number;
+};
+
+export function videoFit$(
+  scope: ObservableScope,
+  videoSize$: Observable<Size | undefined>,
+  tileSize$: Observable<Size | undefined>,
+): Behavior<"cover" | "contain"> {
+  const fit$ = combineLatest([videoSize$, tileSize$]).pipe(
+    map(([videoSize, tileSize]) => {
+      if (!videoSize || !tileSize) {
+        // If we don't have the sizes, default to cover to avoid black bars.
+        // This is a reasonable default as it will ensure the video fills the tile, even if it means cropping.
+        return "cover";
+      }
+      const videoAspectRatio = videoSize.width / videoSize.height;
+      const tileAspectRatio = tileSize.width / tileSize.height;
+
+      // If video is landscape (ratio > 1) and tile is portrait (ratio < 1) or vice versa,
+      // we want to use "contain" (fit) mode to avoid excessive cropping
+      const videoIsLandscape = videoAspectRatio > 1;
+      const tileIsLandscape = tileAspectRatio > 1;
+
+      // If the orientations are the same, use the cover mode (Preserves the aspect ratio, and the image fills the container.)
+      // If they're not the same orientation, use the contain mode (Preserves the aspect ratio, but the image is letterboxed - black bars- to fit within the container.)
+      return videoIsLandscape === tileIsLandscape ? "cover" : "contain";
+    }),
+  );
+
+  return scope.behavior(fit$, "cover");
+}
+
+/**
+ * Helper function to get the video size from a participant.
+ * It observes the participant's video track stats and extracts the frame width and height.
+ * @param participant$ - an Observable of a LocalParticipant or RemoteParticipant, or null if no participant is selected.
+ * @returns an Observable of the video size (width and height) or undefined if the size cannot be determined.
+ */
+export function videoSizeFromParticipant$(
+  participant$: Observable<LocalParticipant | RemoteParticipant | null>,
+): Observable<{ width: number; height: number } | undefined> {
+  return participant$
+    .pipe(
+      // If we have a participant, observe their video track stats. If not, return undefined.
+      switchMap((p) => {
+        if (!p) return of(undefined);
+        if (p.isLocal) {
+          return observeOutboundRtpStreamStats$(p, Track.Source.Camera);
+        } else {
+          return observeInboundRtpStreamStats$(p, Track.Source.Camera);
+        }
+      }),
+    )
+    .pipe(
+      // Extract the frame width and height from the stats. If we don't have valid stats, return undefined.
+      map((stats) => {
+        if (!stats) return undefined;
+        if (
+          // For video tracks, frameWidth and frameHeight should be numbers. If they're not, we can't determine the size.
+          typeof stats.frameWidth !== "number" ||
+          typeof stats.frameHeight !== "number"
+        ) {
+          return undefined;
+        }
+        return {
+          width: stats.frameWidth,
+          height: stats.frameHeight,
+        };
+      }),
+    );
+}