diff --git a/pages/index.vue b/pages/index.vue
index 51ba3cf..3e3df27 100644
--- a/pages/index.vue
+++ b/pages/index.vue
@@ -60,7 +60,7 @@
 
         <div>
           <p class="mb-2 text-sm font-medium text-zinc-300">Aspect ratio / quality</p>
-          <div class="grid grid-cols-3 gap-2">
+          <div class="grid grid-cols-2 gap-2 lg:grid-cols-4">
             <button
               v-for="option in aspects"
               :key="option.id"
@@ -70,9 +70,10 @@
               @click="aspect = option.id"
             >
               <span class="block font-semibold">{{ option.label }}</span>
-              <span class="text-xs text-zinc-400">{{ option.hint }}</span>
+              <span class="text-xs text-zinc-400">{{ option.id === 'auto' ? autoHint : option.hint }}</span>
             </button>
           </div>
+          <p class="mt-2 text-xs text-zinc-500">Output {{ outputSize.width }} × {{ outputSize.height }}{{ aspect === 'auto' ? ' · matching the still' : ' · override' }}</p>
         </div>
 
         <details class="rounded-2xl border border-white/10 bg-zinc-950/40 px-4 py-3">
@@ -140,13 +141,14 @@
             <video
               v-if="videoUrl"
               :src="videoUrl"
-              class="aspect-video w-full bg-black"
+              class="w-full bg-black"
+              :style="{ aspectRatio: `${outputSize.width} / ${outputSize.height}` }"
               controls
               autoplay
               loop
               playsinline
             />
-            <div v-else class="flex aspect-video items-center justify-center text-sm text-zinc-500">
+            <div v-else class="flex items-center justify-center text-sm text-zinc-500" :style="{ aspectRatio: `${outputSize.width} / ${outputSize.height}` }">
               Generated MP4 appears here
             </div>
           </div>
@@ -193,9 +195,12 @@
 </template>
 
 <script setup lang="ts">
+type AspectId = 'auto' | '16:9' | '9:16' | '1:1'
+
 interface HistoryItem {
   id: string
   prompt: string
+  aspect?: AspectId
   width: number
   height: number
   steps: number
@@ -206,18 +211,27 @@ interface HistoryItem {
   createdAt: number
 }
 
+const PRESETS: Record<Exclude<AspectId, 'auto'>, { width: number; height: number }> = {
+  '16:9': { width: 1344, height: 768 },
+  '9:16': { width: 768, height: 1344 },
+  '1:1': { width: 1024, height: 1024 }
+}
+
 const aspects = [
-  { id: '16:9', label: '16:9 Landscape', hint: '1344 × 768 · 0.98 MP' },
-  { id: '9:16', label: '9:16 Portrait', hint: '768 × 1344 · 0.98 MP' },
-  { id: '1:1', label: '1:1 Square', hint: '1024 × 1024' }
-] as const
+  { id: 'auto' as const, label: 'Automatic', hint: 'Match the still' },
+  { id: '16:9' as const, label: '16:9 Landscape', hint: '1344 × 768 · 0.98 MP' },
+  { id: '9:16' as const, label: '9:16 Portrait', hint: '768 × 1344 · 0.98 MP' },
+  { id: '1:1' as const, label: '1:1 Square', hint: '1024 × 1024' }
+]
 
 const fileInput = ref<HTMLInputElement | null>(null)
 const file = ref<File | null>(null)
 const preview = ref('')
 const dragging = ref(false)
 const prompt = ref('')
-const aspect = ref<'16:9' | '9:16' | '1:1'>('16:9')
+const aspect = ref<AspectId>('auto')
+const imageWidth = ref(0)
+const imageHeight = ref(0)
 const turbo = ref(true)
 const duration = ref(5)
 const seedInput = ref('random')
@@ -244,6 +258,36 @@ const elapsedLabel = computed(() => {
   return `${mm}:${ss}`
 })
 
+function snap32(value: number) {
+  return Math.max(32, Math.round(value / 32) * 32)
+}
+
+function autoResolution(srcWidth: number, srcHeight: number) {
+  const ratio = srcWidth / Math.max(srcHeight, 1)
+  let width: number
+  let height: number
+  if (ratio >= 1) {
+    height = 768
+    width = Math.min(1344, height * ratio)
+  } else {
+    width = 768
+    height = Math.min(1344, width / ratio)
+  }
+  return { width: snap32(width), height: snap32(height) }
+}
+
+const outputSize = computed(() => {
+  if (aspect.value !== 'auto') return PRESETS[aspect.value]
+  if (imageWidth.value && imageHeight.value) return autoResolution(imageWidth.value, imageHeight.value)
+  return { width: 1344, height: 768 }
+})
+
+const autoHint = computed(() => {
+  if (!imageWidth.value || !imageHeight.value) return 'Match the still'
+  const size = autoResolution(imageWidth.value, imageHeight.value)
+  return `${size.width} × ${size.height} · from still`
+})
+
 onMounted(async () => {
   history.value = JSON.parse(localStorage.getItem('aigen-history') || '[]')
   const [health, me] = await Promise.all([
@@ -271,12 +315,20 @@ function toast(message: string) {
 function resetImage() {
   file.value = null
   preview.value = ''
+  imageWidth.value = 0
+  imageHeight.value = 0
   if (fileInput.value) fileInput.value.value = ''
 }
 
 function readFile(next: File) {
   file.value = next
   preview.value = URL.createObjectURL(next)
+  const img = new Image()
+  img.onload = () => {
+    imageWidth.value = img.naturalWidth
+    imageHeight.value = img.naturalHeight
+  }
+  img.src = preview.value
 }
 
 function onFile(event: Event) {
@@ -313,9 +365,7 @@ function rerun(item: HistoryItem) {
   prompt.value = item.prompt
   turbo.value = item.turbo
   seedInput.value = String(item.seed)
-  if (item.width === 768) aspect.value = '9:16'
-  else if (item.width === 1024) aspect.value = '1:1'
-  else aspect.value = '16:9'
+  aspect.value = item.aspect || 'auto'
   toast('Settings restored. Drop the same still if it is not already loaded.')
 }
 
@@ -331,6 +381,8 @@ async function generate() {
     body.append('image', file.value)
     body.append('prompt', prompt.value.trim())
     body.append('aspect', aspect.value)
+    body.append('width', String(outputSize.value.width))
+    body.append('height', String(outputSize.value.height))
     body.append('turbo', String(turbo.value))
     body.append('steps', String(turbo.value ? 8 : 20))
     body.append('duration', String(duration.value))
@@ -369,6 +421,7 @@ function listen(id: string, meta: { seed: number; width: number; height: number;
       history.value.unshift({
         id,
         prompt: prompt.value.trim(),
+        aspect: aspect.value,
         width: meta.width,
         height: meta.height,
         steps: meta.steps,
diff --git a/server/api/generate.post.ts b/server/api/generate.post.ts
index 9e85276..f4f9b10 100644
--- a/server/api/generate.post.ts
+++ b/server/api/generate.post.ts
@@ -1,13 +1,3 @@
-const ASPECTS: Record<string, { width: number; height: number }> = {
-  '16:9': { width: 1344, height: 768 },
-  '9:16': { width: 768, height: 1344 },
-  '1:1': { width: 1024, height: 1024 }
-}
-
-function snap32(value: number) {
-  return Math.max(32, Math.round(value / 32) * 32)
-}
-
 function frameLength(seconds: number) {
   const raw = Math.max(5, Math.round(seconds * 24))
   return raw + (5 - (raw % 17) + 17) % 17
@@ -37,9 +27,7 @@ export default defineEventHandler(async (event) => {
     throw createError({ statusCode: 400, statusMessage: 'A motion prompt is required' })
   }
 
-  const aspect = ASPECTS[fields.aspect] || ASPECTS['16:9']
-  const width = snap32(Number(fields.width || aspect.width))
-  const height = snap32(Number(fields.height || aspect.height))
+  const { width, height } = resolveOutputSize(fields.aspect, image.data, Number(fields.width), Number(fields.height))
   const turbo = fields.turbo !== 'false'
   const steps = Number(fields.steps || (turbo ? 8 : 20))
   const seed = fields.seed && fields.seed !== 'random'
@@ -64,6 +52,7 @@ export default defineEventHandler(async (event) => {
     seed,
     width,
     height,
+    aspect: fields.aspect || 'auto',
     steps,
     turbo
   }
diff --git a/server/utils/resolution.ts b/server/utils/resolution.ts
new file mode 100644
index 0000000..6e86a7d
--- /dev/null
+++ b/server/utils/resolution.ts
@@ -0,0 +1,100 @@
+const SHORT_EDGE = 768
+const LONG_EDGE = 1344
+
+export const ASPECT_PRESETS: Record<string, { width: number; height: number }> = {
+  '16:9': { width: 1344, height: 768 },
+  '9:16': { width: 768, height: 1344 },
+  '1:1': { width: 1024, height: 1024 }
+}
+
+export function snap32(value: number) {
+  return Math.max(32, Math.round(value / 32) * 32)
+}
+
+/** Fit the source still to H3's native 768 short-edge canvas, 32px grid, 1344 long-edge cap. */
+export function autoResolution(srcWidth: number, srcHeight: number) {
+  const ratio = srcWidth / Math.max(srcHeight, 1)
+  let width: number
+  let height: number
+  if (ratio >= 1) {
+    height = SHORT_EDGE
+    width = Math.min(LONG_EDGE, height * ratio)
+  } else {
+    width = SHORT_EDGE
+    height = Math.min(LONG_EDGE, width / ratio)
+  }
+  width = snap32(width)
+  height = snap32(height)
+  if (width > LONG_EDGE) width = LONG_EDGE
+  if (height > LONG_EDGE) height = LONG_EDGE
+  return { width: Math.max(32, width), height: Math.max(32, height) }
+}
+
+export function imageDimensions(buf: Buffer) {
+  if (buf.length < 24) return null
+  if (buf[0] === 0x89 && buf[1] === 0x50 && buf[2] === 0x4e && buf[3] === 0x47) {
+    return { width: buf.readUInt32BE(16), height: buf.readUInt32BE(20) }
+  }
+  if (buf[0] === 0x47 && buf[1] === 0x49 && buf[2] === 0x46) {
+    return { width: buf.readUInt16LE(6), height: buf.readUInt16LE(8) }
+  }
+  if (buf[0] === 0x42 && buf[1] === 0x4d && buf.length >= 26) {
+    return { width: buf.readInt32LE(18), height: Math.abs(buf.readInt32LE(22)) }
+  }
+  if (buf.toString('ascii', 0, 4) === 'RIFF' && buf.toString('ascii', 8, 12) === 'WEBP') {
+    return webpSize(buf)
+  }
+  if (buf[0] === 0xff && buf[1] === 0xd8) {
+    return jpegSize(buf)
+  }
+  return null
+}
+
+function webpSize(buf: Buffer) {
+  const kind = buf.toString('ascii', 12, 16)
+  if (kind === 'VP8X' && buf.length >= 30) {
+    const width = 1 + buf[24] + (buf[25] << 8) + (buf[26] << 16)
+    const height = 1 + buf[27] + (buf[28] << 8) + (buf[29] << 16)
+    return { width, height }
+  }
+  if (kind === 'VP8 ' && buf.length >= 30) {
+    return { width: buf.readUInt16LE(26) & 0x3fff, height: buf.readUInt16LE(28) & 0x3fff }
+  }
+  if (kind === 'VP8L' && buf.length >= 25) {
+    const bits = buf.readUInt32LE(21)
+    return { width: (bits & 0x3fff) + 1, height: ((bits >> 14) & 0x3fff) + 1 }
+  }
+  return null
+}
+
+function jpegSize(buf: Buffer) {
+  let offset = 2
+  while (offset + 9 < buf.length) {
+    if (buf[offset] !== 0xff) return null
+    const marker = buf[offset + 1]
+    if (marker === 0xd8 || marker === 0xd9) {
+      offset += 2
+      continue
+    }
+    const length = buf.readUInt16BE(offset + 2)
+    if (marker >= 0xc0 && marker <= 0xc3) {
+      return { width: buf.readUInt16BE(offset + 7), height: buf.readUInt16BE(offset + 5) }
+    }
+    offset += 2 + length
+  }
+  return null
+}
+
+export function resolveOutputSize(aspect: string | undefined, image: Buffer, fallbackWidth?: number, fallbackHeight?: number) {
+  if (aspect && ASPECT_PRESETS[aspect]) {
+    return ASPECT_PRESETS[aspect]
+  }
+  const fromFields = Number(fallbackWidth) && Number(fallbackHeight)
+    ? { width: snap32(Number(fallbackWidth)), height: snap32(Number(fallbackHeight)) }
+    : null
+  const size = imageDimensions(image)
+  if (size?.width && size?.height) {
+    return autoResolution(size.width, size.height)
+  }
+  return fromFields || ASPECT_PRESETS['16:9']
+}