Selenium Fetcher - when using deprecated/not-recommended selenium 3, Some sites - Exception: cannot write mode RGBA as JPEG

[tycho40]

I'm trying to follow the page "https://www.sonos.com/en-us/shop/five-b-stock" as Text but I'm getting the error "Exception: cannot write mode RGBA as JPEG"

Running v0.52.5 in a Docker container.
Share this link: https://changedetection.io/share/PdQl0uf_u-Aa

Thank you for the help!

[dgtlmoon]

can you paste all of the container logs around the error?
can you tell me if its windows or linux or?

[tycho40]

I'm running it on a Synology DSM 7.3.2, with selenium/standalone-chrome-debug:3.141.59 as the webdriver. Is that why, it's too out of date?

Here's the logs that I can find:

AssertionError: write() before start_response
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /share-url/c255055b-34ea-405d-8835-eb5635c9062d HTTP/1.1" 302 -
2026-01-15 18:52:39.261 | INFO     | changedetectionio.processors:available_processors:116 - ALLOWED_PROCESSORS set, filtering to: ['text_json_diff', 'restock_diff']
2026-01-15 18:52:39.261 | DEBUG    | changedetectionio.processors:available_processors:122 - Skipping processor 'image_ssim_diff' (not in ALLOWED_PROCESSORS)
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET / HTTP/1.1" 200 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/csrf.js HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/styles/pure-min.css HTTP/1.1" 200 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/jquery-3.6.0.min.js HTTP/1.1" 200 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/styles/flag-icons.min.css HTTP/1.1" 200 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/feather-icons.min.js HTTP/1.1" 200 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/styles/styles.css?v=0.52.5 HTTP/1.1" 200 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/socket.io.min.js HTTP/1.1" 200 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/watch-overview.js HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/realtime.js HTTP/1.1" 200 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/toggle-theme.js HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/modal.js HTTP/1.1" 200 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/hamburger-menu.js HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/language-selector.js HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/search-modal.js HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/flask-toast-bridge.js HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/toast.js HTTP/1.1" 200 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/js/jquery-3.6.0.min.js HTTP/1.1" 200 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/images/google-chrome-icon.png HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/images/copy.svg HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/images/spread-white.svg HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/images/pause.svg HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/images/spread.svg HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/images/bell-off.svg HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/images/play.svg HTTP/1.1" 304 -
172.17.0.1 - - [15/Jan/2026 18:52:39] "GET /static/images/generic_feed-icon.svg HTTP/1.1" 304 -
2026-01-15 18:52:39.448 | DEBUG    | changedetectionio.realtime.socket_server:handle_connect:299 - Socket.IO: Sent initial queue size 0 to new client
2026-01-15 18:52:39.448 | INFO     | changedetectionio.realtime.socket_server:handle_connect:303 - Socket.IO: Client connected
2026-01-15 18:54:19.331 | INFO     | changedetectionio.realtime.socket_server:handle_disconnect:309 - Socket.IO: Client disconnected
172.17.0.1 - - [15/Jan/2026 18:54:19] "GET /socket.io/?EIO=4&transport=websocket HTTP/1.1" 500 -
Error on request:
Traceback (most recent call last):
  File "/usr/local/werkzeug/serving.py", line 370, in run_wsgi
    execute(self.server.app)
  File "/usr/local/werkzeug/serving.py", line 336, in execute
    write(b"")
  File "/usr/local/werkzeug/serving.py", line 261, in write
    assert status_set is not None, "write() before start_response"
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: write() before start_response

[dgtlmoon]

Traceback (most recent call last):
  File "/usr/local/werkzeug/serving.py", line 370, in run_wsgi
    execute(self.server.app)
  File "/usr/local/werkzeug/serving.py", line 336, in execute
    write(b"")
  File "/usr/local/werkzeug/serving.py", line 261, in write
    assert status_set is not None, "write() before start_response"
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: write() before start_response

this is not the error, this is just the web browser disconnecting :)

can you find it in the logs?

[tycho40]

Ok, I found it! Thank you for your patience! 😊

2026-01-15 19:19:04.531 | DEBUG    | changedetectionio.realtime.socket_server:handle_connect:299 - Socket.IO: Sent initial queue size 0 to new client
2026-01-15 19:19:04.532 | INFO     | changedetectionio.realtime.socket_server:handle_connect:303 - Socket.IO: Client connected
2026-01-15 19:22:00.081 | DEBUG    | changedetectionio.realtime.events:handle_watch_operation:16 - Socket.IO: Received watch operation 'recheck' for UUID c255055b-34ea-405d-8835-eb5635c9062d
2026-01-15 19:22:00.083 | DEBUG    | changedetectionio.realtime.socket_server:handle_queue_length:109 - SignalHandler: Queue length update received: 0
2026-01-15 19:22:00.083 | DEBUG    | changedetectionio.queue_handlers:get:104 - Successfully retrieved item: c255055b-34ea-405d-8835-eb5635c9062d
2026-01-15 19:22:00.084 | DEBUG    | changedetectionio.realtime.socket_server:handle_queue_length:109 - SignalHandler: Queue length update received: 0
2026-01-15 19:22:00.084 | DEBUG    | changedetectionio.worker_handler:set_uuid_processing:206 - Worker 2 started processing UUID: c255055b-34ea-405d-8835-eb5635c9062d
2026-01-15 19:22:00.085 | DEBUG    | changedetectionio.queue_handlers:put:72 - Successfully queued item: c255055b-34ea-405d-8835-eb5635c9062d
2026-01-15 19:22:00.085 | INFO     | changedetectionio.async_update_worker:async_update_worker:108 - Worker 2 processing watch UUID c255055b-34ea-405d-8835-eb5635c9062d Priority 1 URL https://www.sonos.com/en-us/shop/five-b-stock
2026-01-15 19:22:00.085 | DEBUG    | changedetectionio.worker_handler:queue_item_async_safe:254 - Successfully queued item: c255055b-34ea-405d-8835-eb5635c9062d
2026-01-15 19:22:00.086 | INFO     | changedetectionio.realtime.events:handle_watch_operation:43 - Socket.IO: Queued recheck for watch c255055b-34ea-405d-8835-eb5635c9062d
2026-01-15 19:22:00.089 | DEBUG    | changedetectionio.realtime.socket_server:handle_watch_small_status_update:52 - Socket.IO: Received watch small status update 'Fetching page..' for UUID c255055b-34ea-405d-8835-eb5635c9062d
2026-01-15 19:22:00.089 | DEBUG    | changedetectionio.processors.base:call_browser:96 - Using proxy 'None' for c255055b-34ea-405d-8835-eb5635c9062d
2026-01-15 19:22:17.404 | ERROR    | changedetectionio.async_update_worker:async_update_worker:321 - Worker 2 exception processing watch UUID: c255055b-34ea-405d-8835-eb5635c9062d
2026-01-15 19:22:17.404 | ERROR    | changedetectionio.async_update_worker:async_update_worker:322 - cannot write mode RGBA as JPEG
2026-01-15 19:22:17.405 | DEBUG    | changedetectionio.async_update_worker:async_update_worker:341 - Processing watch UUID: c255055b-34ea-405d-8835-eb5635c9062d - xpath_data length returned empty.
2026-01-15 19:22:17.405 | DEBUG    | changedetectionio.async_update_worker:async_update_worker:416 - Cleared fetcher content for UUID c255055b-34ea-405d-8835-eb5635c9062d
2026-01-15 19:22:17.405 | DEBUG    | changedetectionio.worker_handler:set_uuid_processing:209 - Worker 2 finished processing UUID: c255055b-34ea-405d-8835-eb5635c9062d
2026-01-15 19:22:17.464 | DEBUG    | changedetectionio.async_update_worker:async_update_worker:469 - Worker 2 completed watch c255055b-34ea-405d-8835-eb5635c9062d in 17.46s

[dgtlmoon]

Which content fetcher? selenium? playwright?

[tycho40]

I'm using selenium/standalone-chrome-debug:3.141.59 also in Docker

[dgtlmoon]

any chance you can switch to sockpuppetbrowser? and let me know if that solves it? selenium doesnt do proper full page screenshots

[dgtlmoon]

Can you confirm that it works fine on some other page?

[dgtlmoon]

@tycho40 try 0.52.6 when its out in a few minutes and please report back if its solved it for you!