diff --git a/js/nostr/nip71.js b/js/nostr/nip71.js
index 069e8b43..44d74579 100644
--- a/js/nostr/nip71.js
+++ b/js/nostr/nip71.js
@@ -1520,6 +1520,15 @@ export function convertEventToVideo(event = {}) {
         .filter((value) => typeof value === "string" && value.trim())
         .map((value) => value.trim())
     : [];
+  const toPositiveInt = (value) => {
+    const n = Number(value);
+    return Number.isFinite(n) && n > 0 ? Math.floor(n) : undefined;
+  };
+  const width = toPositiveInt(parsedContent.width);
+  const height = toPositiveInt(parsedContent.height);
+  const durationValue = Number(parsedContent.duration);
+  const duration =
+    Number.isFinite(durationValue) && durationValue > 0 ? durationValue : undefined;
   const videoRootId = safeTrim(parsedContent.videoRootId) || event.id;
   const wsField = safeTrim(parsedContent.ws);
   const xsField = safeTrim(parsedContent.xs);
@@ -1624,6 +1633,9 @@ export function convertEventToVideo(event = {}) {
     mode,
     deleted,
     hashtags,
+    width,
+    height,
+    duration,
     ws,
     xs,
     storagePointer,
diff --git a/js/nostr/videoPayloadBuilder.js b/js/nostr/videoPayloadBuilder.js
index db3da3af..9410feed 100644
--- a/js/nostr/videoPayloadBuilder.js
+++ b/js/nostr/videoPayloadBuilder.js
@@ -8,6 +8,18 @@ import { inferMimeTypeFromUrl } from "../utils/mime.js";
 import { normalizeHashtag } from "../utils/hashtagNormalization.js";
 import { devLogger } from "../utils/logger.js";
 
+// Pixel dimensions: positive integer or 0 (= "unknown / omit").
+export function normalizeVideoDimension(value) {
+  const n = Number(value);
+  return Number.isFinite(n) && n > 0 ? Math.floor(n) : 0;
+}
+
+// Duration in seconds: positive (float ok) or 0 (= omit).
+export function normalizeVideoDuration(value) {
+  const n = Number(value);
+  return Number.isFinite(n) && n > 0 ? n : 0;
+}
+
 // Normalize free-form hashtag input (array or comma/space string) to a deduped,
 // lowercased list. Drops the reserved "video" topic tag and caps the count.
 export function sanitizeVideoHashtags(input) {
@@ -191,6 +203,21 @@ export async function prepareVideoPublishPayload(videoPayload, pubkey, { timesta
       contentObject.hashtags = hashtags;
     }
 
+    // Captured-at-upload dimensions/duration: persist so a video's orientation is
+    // known durably (drives 34236 short selection + a future "shorts" feed filter).
+    const width = normalizeVideoDimension(videoData.width);
+    const height = normalizeVideoDimension(videoData.height);
+    const duration = normalizeVideoDuration(videoData.duration);
+    if (width) {
+      contentObject.width = width;
+    }
+    if (height) {
+      contentObject.height = height;
+    }
+    if (duration) {
+      contentObject.duration = duration;
+    }
+
     const nip71Tags = buildNip71MetadataTags(
       nip71Metadata && typeof nip71Metadata === "object" ? nip71Metadata : null
     );
@@ -484,6 +511,20 @@ export function prepareVideoEditPayload(params) {
   }
   const hashtagTags = hashtags.map((tag) => ["t", tag]);
 
+  // Preserve captured dimensions/duration across edits (prefer edited values).
+  const width = normalizeVideoDimension(updatedData?.width ?? baseEvent.width);
+  const height = normalizeVideoDimension(updatedData?.height ?? baseEvent.height);
+  const duration = normalizeVideoDuration(updatedData?.duration ?? baseEvent.duration);
+  if (width) {
+    contentObject.width = width;
+  }
+  if (height) {
+    contentObject.height = height;
+  }
+  if (duration) {
+    contentObject.duration = duration;
+  }
+
   let metadataForTags =
     nip71Metadata && typeof nip71Metadata === "object" ? nip71Metadata : null;
   if (!metadataForTags) {
diff --git a/js/ui/components/UploadModal.js b/js/ui/components/UploadModal.js
index f4344088..fa618431 100644
--- a/js/ui/components/UploadModal.js
+++ b/js/ui/components/UploadModal.js
@@ -1,6 +1,7 @@
 // components/UploadModal.js
 import { createModalAccessibility } from "./modalAccessibility.js";
 import { Nip71FormManager } from "./nip71FormManager.js";
+import { probeVideoMetadata } from "../../utils/videoProbe.js";
 import { MediaUploader } from "./mediaUploader.js";
 import { devLogger, userLogger } from "../../utils/logger.js";
 import {
@@ -483,10 +484,35 @@ export class UploadModal {
 
   // --- Immediate Upload Handlers ---
 
+  // Best-effort: read the file's dimensions/duration so we can persist them
+  // (orientation → 34236 short selection + a future "shorts" feed). Never blocks
+  // upload; failures just leave the metadata unset.
+  async captureVideoMetadata(file) {
+      this.capturedMetadata = null;
+      if (!file || typeof URL === "undefined" || typeof URL.createObjectURL !== "function") {
+          return;
+      }
+      const objectUrl = URL.createObjectURL(file);
+      try {
+          this.capturedMetadata = await probeVideoMetadata(objectUrl);
+      } catch (error) {
+          this.capturedMetadata = null;
+      } finally {
+          try {
+              URL.revokeObjectURL(objectUrl);
+          } catch (revokeError) {
+              // ignore
+          }
+      }
+  }
+
   async handleVideoSelection(e) {
       const file = e.target.files?.[0];
       if (!file) return;
 
+      // Probe dimensions/duration in the background while the upload proceeds.
+      void this.captureVideoMetadata(file);
+
       if (!this.storageConfigured) {
           alert("Please configure storage before selecting a file.");
           e.target.value = ""; // Clear selection
@@ -900,6 +926,12 @@ export class UploadModal {
           enableComments: this.toggles.comments?.checked || true,
           ...audienceFlags,
 
+          // Auto-captured at file-select (best-effort; absent ⇒ omitted). Drives
+          // 34236 short selection + a future "shorts" feed (height > width).
+          width: this.capturedMetadata?.width || 0,
+          height: this.capturedMetadata?.height || 0,
+          duration: this.capturedMetadata?.duration || 0,
+
           // These might be empty depending on mode, filled below
           url: "",
           magnet: "",
diff --git a/js/utils/videoProbe.js b/js/utils/videoProbe.js
new file mode 100644
index 00000000..0fdc6bbc
--- /dev/null
+++ b/js/utils/videoProbe.js
@@ -0,0 +1,80 @@
+// Auto-capture a video's dimensions + duration by loading just its metadata into
+// a hidden <video> element. Used at upload time so bitvid can persist width/height
+// (orientation → 34236 short selection + a future "shorts" feed) and duration.
+//
+// Element creation is injectable so the resolution logic is unit-testable without
+// a DOM or a real media file. Always resolves (never rejects): null on failure.
+
+export function probeVideoMetadata(src, { createVideoEl, timeoutMs = 8000 } = {}) {
+  return new Promise((resolve) => {
+    const source = typeof src === "string" ? src.trim() : "";
+    if (!source) {
+      resolve(null);
+      return;
+    }
+
+    let el = null;
+    try {
+      el =
+        typeof createVideoEl === "function"
+          ? createVideoEl()
+          : typeof document !== "undefined" && document.createElement
+            ? document.createElement("video")
+            : null;
+    } catch (error) {
+      el = null;
+    }
+    if (!el || typeof el.addEventListener !== "function") {
+      resolve(null);
+      return;
+    }
+
+    let settled = false;
+    const cleanup = () => {
+      try {
+        el.removeAttribute?.("src");
+        el.load?.();
+      } catch (error) {
+        // ignore
+      }
+    };
+    const finish = (result) => {
+      if (settled) {
+        return;
+      }
+      settled = true;
+      clearTimeout(timer);
+      cleanup();
+      resolve(result);
+    };
+
+    const timer = setTimeout(() => finish(null), timeoutMs);
+
+    try {
+      el.preload = "metadata";
+      el.muted = true;
+    } catch (error) {
+      // ignore (fakes may not allow these)
+    }
+
+    el.addEventListener("loadedmetadata", () => {
+      const width = Number(el.videoWidth);
+      const height = Number(el.videoHeight);
+      const durationRaw = Number(el.duration);
+      finish({
+        width: Number.isFinite(width) && width > 0 ? Math.floor(width) : 0,
+        height: Number.isFinite(height) && height > 0 ? Math.floor(height) : 0,
+        duration: Number.isFinite(durationRaw) && durationRaw > 0 ? durationRaw : 0,
+      });
+    });
+    el.addEventListener("error", () => finish(null));
+
+    try {
+      el.src = source;
+    } catch (error) {
+      finish(null);
+    }
+  });
+}
+
+export default probeVideoMetadata;
diff --git a/tests/video-dimensions.test.mjs b/tests/video-dimensions.test.mjs
new file mode 100644
index 00000000..30bf0e5d
--- /dev/null
+++ b/tests/video-dimensions.test.mjs
@@ -0,0 +1,94 @@
+// Dimension capture: width/height/duration are persisted in the 30078 content,
+// survive edits, parse back onto the video, and drive the NIP-71 mirror's
+// normal(34235)-vs-short(34236) selection + imeta dim. (Foundation for a future
+// "shorts" vertical feed, which filters on height > width.)
+
+import "./test-helpers/setup-localstorage.mjs";
+import assert from "node:assert/strict";
+import test from "node:test";
+import {
+  prepareVideoPublishPayload,
+  prepareVideoEditPayload,
+  normalizeVideoDimension,
+} from "../js/nostr/videoPayloadBuilder.js";
+import { convertEventToVideo } from "../js/nostr/nip71.js";
+import {
+  buildNip71MirrorEvent,
+  NIP71_NORMAL_VIDEO_KIND,
+  NIP71_SHORT_VIDEO_KIND,
+} from "../js/nostr/nip71Mirror.js";
+
+const PUBKEY = "a".repeat(64);
+
+function publish(extra) {
+  return prepareVideoPublishPayload(
+    { title: "Hi", url: "https://cdn.example.com/v.mp4", ...extra },
+    PUBKEY,
+    { timestamp: 1000 },
+  );
+}
+
+test("normalizeVideoDimension: positive int or 0", () => {
+  assert.equal(normalizeVideoDimension(1920), 1920);
+  assert.equal(normalizeVideoDimension("1080"), 1080);
+  assert.equal(normalizeVideoDimension(0), 0);
+  assert.equal(normalizeVideoDimension(-5), 0);
+  assert.equal(normalizeVideoDimension("abc"), 0);
+});
+
+test("publish persists width/height/duration in content; parser exposes them", async () => {
+  const { event } = await publish({
+    videoRootId: "root-1",
+    width: 1080,
+    height: 1920,
+    duration: 42.5,
+  });
+  const content = JSON.parse(event.content);
+  assert.equal(content.width, 1080);
+  assert.equal(content.height, 1920);
+  assert.equal(content.duration, 42.5);
+
+  const video = convertEventToVideo(event);
+  assert.equal(video.width, 1080);
+  assert.equal(video.height, 1920);
+  assert.equal(video.duration, 42.5);
+});
+
+test("a portrait (height>width) video mirrors as 34236 short with imeta dim", async () => {
+  const { event } = await publish({ videoRootId: "root-2", width: 1080, height: 1920 });
+  const video = convertEventToVideo(event);
+  const res = buildNip71MirrorEvent({ ...video, pubkey: PUBKEY });
+  assert.equal(res.event.kind, NIP71_SHORT_VIDEO_KIND, "portrait => 34236");
+  const imeta = res.event.tags.find((t) => t[0] === "imeta");
+  assert.ok(imeta.some((e) => e === "dim 1080x1920"), "carries imeta dim");
+});
+
+test("a landscape video mirrors as 34235 normal", async () => {
+  const { event } = await publish({ videoRootId: "root-3", width: 1920, height: 1080 });
+  const video = convertEventToVideo(event);
+  const res = buildNip71MirrorEvent({ ...video, pubkey: PUBKEY });
+  assert.equal(res.event.kind, NIP71_NORMAL_VIDEO_KIND, "landscape => 34235");
+});
+
+test("editing preserves dimensions when the field is omitted", () => {
+  const { contentObject } = prepareVideoEditPayload({
+    baseEvent: {
+      id: "e1",
+      videoRootId: "root-9",
+      title: "Old",
+      url: "https://cdn.example.com/v.mp4",
+      width: 1280,
+      height: 720,
+      duration: 30,
+      created_at: 1000,
+      tags: [],
+    },
+    originalEventStub: { id: "e1" },
+    updatedData: { title: "New" },
+    userPubkey: PUBKEY,
+    resolveEventDTag: () => "root-9",
+  });
+  assert.equal(contentObject.width, 1280);
+  assert.equal(contentObject.height, 720);
+  assert.equal(contentObject.duration, 30);
+});
diff --git a/tests/video-probe.test.mjs b/tests/video-probe.test.mjs
new file mode 100644
index 00000000..e0768cc0
--- /dev/null
+++ b/tests/video-probe.test.mjs
@@ -0,0 +1,59 @@
+// probeVideoMetadata resolves a video's dimensions/duration from a hidden element,
+// or null on error/timeout. Uses an injected fake element so it's deterministic.
+
+import assert from "node:assert/strict";
+import test from "node:test";
+import { probeVideoMetadata } from "../js/utils/videoProbe.js";
+
+// Minimal fake <video>: fires the named event on the next tick when src is set.
+function fakeVideo({ fire = "loadedmetadata", videoWidth = 0, videoHeight = 0, duration = 0 } = {}) {
+  const handlers = {};
+  return {
+    videoWidth,
+    videoHeight,
+    duration,
+    addEventListener(name, h) {
+      handlers[name] = h;
+    },
+    removeAttribute() {},
+    load() {},
+    set src(_v) {
+      setTimeout(() => handlers[fire]?.(), 0);
+    },
+  };
+}
+
+test("resolves width/height/duration from loadedmetadata", async () => {
+  const result = await probeVideoMetadata("blob:abc", {
+    createVideoEl: () => fakeVideo({ videoWidth: 1080, videoHeight: 1920, duration: 12.3 }),
+  });
+  assert.deepEqual(result, { width: 1080, height: 1920, duration: 12.3 });
+});
+
+test("a portrait probe yields height > width (drives short selection)", async () => {
+  const r = await probeVideoMetadata("blob:abc", {
+    createVideoEl: () => fakeVideo({ videoWidth: 720, videoHeight: 1280 }),
+  });
+  assert.ok(r.height > r.width);
+  assert.equal(r.duration, 0, "missing duration normalizes to 0");
+});
+
+test("resolves null on a media error", async () => {
+  const r = await probeVideoMetadata("blob:bad", {
+    createVideoEl: () => fakeVideo({ fire: "error" }),
+  });
+  assert.equal(r, null);
+});
+
+test("resolves null for an empty source and times out gracefully", async () => {
+  assert.equal(await probeVideoMetadata("", { createVideoEl: () => fakeVideo() }), null);
+  // never fires any event -> timeout path
+  const neverFires = {
+    addEventListener() {},
+    removeAttribute() {},
+    load() {},
+    set src(_v) {},
+  };
+  const r = await probeVideoMetadata("blob:x", { createVideoEl: () => neverFires, timeoutMs: 20 });
+  assert.equal(r, null);
+});