diff --git a/app/api/jobs.py b/app/api/jobs.py
index 7fc8df8b..17dc365c 100644
--- a/app/api/jobs.py
+++ b/app/api/jobs.py
@@ -33,8 +33,8 @@
 router = APIRouter(tags=["jobs"])
 logger = logging.getLogger("stemdeck.api")
 
-_ALLOWED_EXTS = frozenset((".mp3", ".wav", ".flac"))
-_MAX_UPLOAD_BYTES = 100 * 1024 * 1024  # 100 MB
+_ALLOWED_EXTS = frozenset((".mp3", ".wav", ".flac", ".mp4", ".m4a"))
+_MAX_UPLOAD_BYTES = 400 * 1024 * 1024  # 400 MB
 _WS_RE = re.compile(r"\s+")
 
 
@@ -161,7 +161,7 @@ async def _create_local_job(request: Request) -> dict[str, str]:
     if cl_header:
         try:
             if int(cl_header) > _MAX_UPLOAD_BYTES + 4096:
-                raise HTTPException(status_code=422, detail="File exceeds 100 MB limit")
+                raise HTTPException(status_code=422, detail="File exceeds 400 MB limit")
         except ValueError:
             pass
 
@@ -177,7 +177,7 @@ async def _create_local_job(request: Request) -> dict[str, str]:
     if ext not in _ALLOWED_EXTS:
         raise HTTPException(
             status_code=422,
-            detail=f"Unsupported file type '{ext}': only .mp3, .wav, and .flac are accepted",
+            detail=f"Unsupported file type '{ext}': accepted formats are .mp3, .wav, .flac, .mp4, and .m4a",
         )
 
     # Validate stems list from form field
@@ -196,7 +196,7 @@ async def _create_local_job(request: Request) -> dict[str, str]:
     if file_size == 0:
         raise HTTPException(status_code=422, detail="Uploaded file is empty")
     if file_size > _MAX_UPLOAD_BYTES:
-        raise HTTPException(status_code=422, detail="File exceeds 100 MB limit")
+        raise HTTPException(status_code=422, detail="File exceeds 400 MB limit")
 
     job_id = uuid.uuid4().hex[:12]
     job_dir = JOBS_DIR / job_id
diff --git a/static/index.html b/static/index.html
index f8bb80fb..4c237898 100644
--- a/static/index.html
+++ b/static/index.html
@@ -57,7 +57,7 @@
                 <path d="M12 3v12 M7 8l5-5 5 5 M5 21h14"/>
               </svg>
             </button>
-            <input id="fileInput" type="file" accept=".mp3,.wav,.flac,audio/mpeg,audio/wav,audio/flac" style="display:none" aria-hidden="true" />
+            <input id="fileInput" type="file" accept=".mp3,.wav,.flac,.mp4,.m4a,audio/mpeg,audio/wav,audio/flac,video/mp4,audio/mp4" style="display:none" aria-hidden="true" />
           </div>
 
           <!-- Divider -->
diff --git a/static/js/main.js b/static/js/main.js
index 0d71b6d1..2f1821c1 100644
--- a/static/js/main.js
+++ b/static/js/main.js
@@ -271,17 +271,18 @@ function wireFileDrop() {
     return n < 1024 * 1024 ? `${(n / 1024).toFixed(0)} KB` : `${(n / 1024 / 1024).toFixed(1)} MB`;
   }
 
-  const MAX_UPLOAD_BYTES = 100 * 1024 * 1024; // must match server _MAX_UPLOAD_BYTES
+  const MAX_UPLOAD_BYTES = 400 * 1024 * 1024; // must match server _MAX_UPLOAD_BYTES
 
   function applyFile(file) {
     if (!file) return;
     const lower = file.name.toLowerCase();
-    if (!lower.endsWith(".mp3") && !lower.endsWith(".wav") && !lower.endsWith(".flac")) {
-      showError("Only MP3, WAV, and FLAC files are supported.");
+    if (!lower.endsWith(".mp3") && !lower.endsWith(".wav") && !lower.endsWith(".flac") &&
+        !lower.endsWith(".mp4") && !lower.endsWith(".m4a")) {
+      showError("Only MP3, WAV, FLAC, MP4, and M4A files are supported.");
       return;
     }
     if (file.size > MAX_UPLOAD_BYTES) {
-      showError(`File is too large (${formatBytes(file.size)}). Maximum is 100 MB.`);
+      showError(`File is too large (${formatBytes(file.size)}). Maximum is 400 MB.`);
       return;
     }
     if (fileName) fileName.textContent = file.name;