ASS alignment broken

mpv Information

[ 809.921][v][cplayer] mpv v0.39.0-1025-g6c4218252 Copyright © 2000-2025 mpv/MPlayer/mplayer2 projects
[ 809.922][v][cplayer]  built on Mar 17 2025 17:11:55
[ 809.922][v][cplayer] libplacebo version: v7.350.0 (v7.349.0-61-g16ef0a2-dirty)
[ 809.922][v][cplayer] FFmpeg version: N-118854-g2471b2202
[ 809.922][v][cplayer] FFmpeg library versions:
[ 809.922][v][cplayer]    libavcodec      61.33.102
[ 809.922][v][cplayer]    libavdevice     61.4.100
[ 809.922][v][cplayer]    libavfilter     10.9.100
[ 809.922][v][cplayer]    libavformat     61.9.107
[ 809.922][v][cplayer]    libavutil       59.60.100
[ 809.922][v][cplayer]    libswresample   5.4.100
[ 809.922][v][cplayer]    libswscale      8.13.102
[ 809.922][v][cplayer] Configuration: -Ddebug=true -Db_ndebug=true -Doptimization=3 -Db_lto=true -Dlibmpv=true -Dpdf-build=enabled -Dlua=enabled -Djavascript=enabled -Dsdl2=enabled -Dlibarchive=enabled -Dlibbluray=enabled -Ddvdnav=enabled -Duchardet=enabled -Drubberband=enabled -Dlcms2=enabled -Dopenal=enabled -Dspirv-cross=enabled -Dvulkan=enabled -Dvapoursynth=enabled -Dgl=enabled -Degl-angle=enabled -Dc_args=-Wno-error=int-conversion -Dprefix=/__w/mpv-winbuild/mpv-winbuild/mpv-winbuild-cmake/build32/install/i686-w64-mingw32 -Dlibdir=/__w/mpv-winbuild/mpv-winbuild/mpv-winbuild-cmake/build32/install/i686-w64-mingw32/lib -Ddefault_library=shared -Dprefer_static=True --cross-file=/__w/mpv-winbuild/mpv-winbuild/mpv-winbuild-cmake/build32/meson_cross.txt
[ 809.922][v][cplayer] List of enabled features: build-date cplugins cuda-hwaccel cuda-interop d3d-hwaccel d3d11 d3d9-hwaccel debug direct3d dos-paths dvdnav dxgi-debug-d3d11 egl-angle egl-angle-win32 ffmpeg ffnvcodec gl gl-dxinterop gl-dxinterop-d3d9 gl-win32 glob glob-win32 gpl iconv javascript jpeg lcms2 libarchive libass libavdevice libbluray libplacebo luajit openal rubberband rubberband-3 sdl2 sdl2-audio sdl2-gamepad sdl2-video shaderc spirv-cross uchardet vaapi vaapi-win32 vapoursynth vector vk-khr-display vulkan wasapi win32 win32-desktop win32-executable win32-smtc win32-threads zimg zimg-st428 zlib
[ 809.922][v][cplayer] Built with NDEBUG.

Other Information

- Windows version: Windows 10 Pro 64-bit (10.0, Build 19045) (19041.vb_release.191206-1406)
- GPU model, driver and version:AMD Radeon(TM) Graphics
- Source of mpv: https://github.com/wbtcpip2/mpv-winbuild/releases/tag/2025-03-17-6c42182
- Latest known working version:
- Issue started after the following happened:

Reproduction Steps

i use show-text to display a short text top-center aligned
"${osd-ass-cc/0}{\an8}${osd-ass-cc/1}panoramica dalla turchia"
and it shows correctly top-center aligned

but if i add the "pos" code the alignment is wrong
"${osd-ass-cc/0}{\an8}{\pos(0,40)}${osd-ass-cc/1}panoramica dalla turchia"

Expected Behavior

i expect that using the pos coordinate the center alignment should not be broke

Actual Behavior

when using the pos code the alignment is broke

Log File

correct alignment:

18032025_191247_E100VIDEOVID00003MP4.txt

wrong alignment:

18032025_191151_E100VIDEOVID00003MP4.txt

Sample Files

No response

I carefully read all instruction and confirm that I did the following:

• I tested with the latest mpv version to validate that the issue is not already fixed.
• I provided all required information including system and mpv version.
• I produced the log file with the exact same set of files, parameters, and conditions used in "Reproduction Steps", with the addition of --log-file=output.txt.
• I produced the log file while the behaviors described in "Actual Behavior" were actively observed.
• I attached the full, untruncated log file.
• I attached the backtrace in the case of a crash.

Start by reproducing the two ${osd-ass-cc} and show-text cases from the issue on the reported Windows setup, then compare the attached logs for the alignment difference. Trace the OSD/ASS rendering path responsible for {\\an8} and {\\pos(0,40)}. Done means the position override preserves the expected top-center alignment.