protonscr

Descenders

protonopen appid 681280Game compatibility - Unofficial
ValveSoftware/Proton#10124 · opened 2026-09-06 by yonie · updated 2026-09-09 · 2 comments · github · game page · search this game
Yyonie 2026-09-06 github

Game: Descenders (appid 681280) — Unity 2017.4.40f1, Windows depot
Regression: works on Proton 9.0 and 10.0, crashes on Proton 11
Tested: 11.0-2c and experimental-11.0-20260903b — both crash
OS/GPU: SteamOS 3.8.26 (beta), Game Mode, Mesa RADV, NAVI33

Symptom

Intermittent crash a few seconds after the window appears, during the boot logo
videos. Roughly 5 of 7 launches on Proton 11; never observed on 9 or 10.

MFReadWrite.dll caused an Access Violation (0xc0000005)
Read from location ffffffff caused an access violation.

Fault

--- Exception 0xc0000005   addr=MFReadWrite.dll+0x8553
info[0]=0000000000000000
info[1]=FFFFFFFFFFFFFFFF
backtrace:
  MFReadWrite.dll + 0x8553
  MFReadWrite.dll + 0x9622
  rtworkq.dll     + 0x3580
  rtworkq.dll     + 0x5957
  ntdll.dll       + 0x6D7AD
  ntdll.dll       + 0x6C668
  kernel32.dll    + 0x11649
  ntdll.dll       + 0x10E0F

Trace

A second MP4 media source is created ~15 ms before the crash, while the first
source reader is still draining stream events on an rtworkq worker thread:

mfplat:presentation_descriptor_SetString ..., MF_PD_MIME_TYPE, L"video/mp4"   <- source #2
...
wg_transform_read_data: Cannot read 3110400 bytes, no output available
...
mfplat:source_reader_stream_events_callback_Invoke ... stream A
mfplat:media_stream_Release stream A, refcount 1
mfplat:source_reader_stream_events_callback_Invoke ... stream B
mfplat:media_stream_Release stream B, refcount 1
--- Exception 0xc0000005

3110400 = 192010801.5, one 1080p frame. The decoder had no output available,
and the source reader then reads through a -1 pointer dispatching a stream event.

Notes on cause

  • Not the video content: replacing the boot videos with a synthetic 1 s black
    clip (H.264 Main, 1080p, 30 fps, silent AAC) reproduces it identically.
  • Not winedmo: Proton 10 ships winedmo and does not crash.
  • The visible difference is ntsync, new in Proton 11 (this title logs
    ntsync: up and running on 11; Proton 10 titles log fsync). PROTON_NO_FSYNC=1
    does not help on 11, as expected — it does not affect ntsync, and there appears
    to be no ntsync opt-out to test against.
  • Timing-sensitive: with heavy WINEDEBUG tracing enabled the crash sometimes
    does not occur, consistent with a race.

Corroboration

A ProtonDB report from ~5 months ago on proton-cachyos describes the same thing:
"Sometimes, game would crash on startup. Goes away after second launch."

Workaround

Force Proton 10 (or 9).

Full PROTON_LOG available on request.

BBlisto91 2026-09-09 github

Hi there and thank you for the report.

Full PROTON_LOG available on request.

Requested

Yyonie 2026-09-09 github

Full PROTON_LOG: https://gist.github.com/yonie/a7eb3720d20aa22a544445f34dff98b3

Freshly captured, default PROTON_LOG=1 channels only — no extra WINEDEBUG, since with heavy tracing on the race usually does not fire.

  • Proton experimental-11.0-20260903b-x86_64, container steamrt4 4.0.20260805.254769
  • SteamOS 3.8.26, Game Mode, kernel 6.18.46-valve1-1-neptune, Mesa RADV NAVI33
  • 4 of 5 launches crashed, each of them ~16 s in, during the boot logo videos

The fault (line 9033 of the log):

warn:seh:dispatch_exception backtrace: --- Exception 0xc0000005.
trace:seh:dispatch_exception code=c0000005 (EXCEPTION_ACCESS_VIOLATION) flags=0 addr=00006FFFFA188553
trace:seh:dispatch_exception  info[0]=0000000000000000
trace:seh:dispatch_exception  info[1]=FFFFFFFFFFFFFFFF
warn:seh:virtual_unwind backtrace: 00006FFFFA188553: L"MFReadWrite.dll" + 0000000000008553.

The three lines directly before it:

fixme:mfplat:MFPluginControl_GetPreferredClsidByIndex (0 0 00000000066EF7C8 00000000066EF7F0)
ERROR aacparse gstaacparse.c:358:gst_aac_parse_sink_setcaps:<aacparse2> Need codec_data for raw AAC
fixme:mfplat:transform_ProcessMessage Ignoring message 0x10000003.

Let me know if you want another run with specific channels enabled, a log from 11.0-2c rather than experimental, or anything else — the machine reproduces this on demand.

Proton versions

Launch options

DLLs

Error codes