Can do both

js/lib/widget.js

@@ -90,8 +90,7 @@ export class RemoteFrameBufferModel extends DOMWidgetModel {
      */
     on_msg(msg, buffers) {
         if (msg.type === 'framebufferdata') {
-            let blob = new Blob([buffers[0].buffer], { type: msg.mimetype });
-            this.frames.push({ ...msg, blob: blob });
+            this.frames.push({ ...msg, buffers: buffers });
         }
     }
 
@@ -142,12 +141,18 @@ export class RemoteFrameBufferModel extends DOMWidgetModel {
         }
         // Pick the oldest frame from the stack
         let frame = this.frames.shift();
-        let new_url = URL.createObjectURL(frame.blob);
-        let old_url = this.img_elements?.[0]?.src;
-        URL.revokeObjectURL(old_url);
+        let new_src;
+        if (frame.buffers.length > 0) {
+            let blob = new Blob([frame.buffers[0].buffer], { type: frame.mimetype });
+            new_src = URL.createObjectURL(blob);
+        } else {
+            new_src = frame.data_b64;
+        }
+        let old_src = this.img_elements?.[0]?.src;
+        if (old_src.startsWith('blob:')) { URL.revokeObjectURL(old_src); }
         // Update the image sources
         for (let img of this.img_elements) {
-            img.src = new_url;
+            img.src = new_src;
         }
         // Let the server know we processed the image (even if it's not shown yet)
         this.last_frame = frame;

jupyter_rfb/widget.py

@@ -14,6 +14,7 @@
 
 import asyncio
 import time
+from base64 import encodebytes
 
 import ipywidgets
 import numpy as np
@@ -90,6 +91,7 @@ def __init__(self, *args, **kwargs):
         self._rfb_last_resize_event = None
         self._rfb_warned_png = False
         self._rfb_lossless_draw_info = None
+        self._use_websocket = False  # Could be a prop, private for now
         # Init stats
         self.reset_stats()
         # Setup events
@@ -285,6 +287,12 @@ def _rfb_send_frame(self, array, is_lossless_redraw=False):
         # Turn array into a based64-encoded JPEG or PNG
         t1 = time.perf_counter()
         mimetype, data = array2compressed(array, quality)
+        if self._use_websocket:
+            datas = [data]
+            data_b64 = None
+        else:
+            datas = []
+            data_b64 = f"data:{mimetype};base64," + encodebytes(data).decode()
         t2 = time.perf_counter()
 
         if "jpeg" in mimetype:
@@ -314,10 +322,11 @@ def _rfb_send_frame(self, array, is_lossless_redraw=False):
         msg = dict(
             type="framebufferdata",
             mimetype=mimetype,
+            data_b64=data_b64,
             index=self._rfb_frame_index,
             timestamp=timestamp,
         )
-        self.send(msg, [data])
+        self.send(msg, datas)
 
     # ----- related to stats