[partially_]seekable property isn't reliable

mpv Information

mpv v0.41.0 Copyright © 2000-2025 mpv/MPlayer/mplayer2 projects
 built on Aug 28 2026 19:44:41
libplacebo version: v7.360.1
FFmpeg version: n9.0.1
FFmpeg library versions:
   libavcodec      63.1.101
   libavdevice     63.1.101
   libavfilter     12.1.101
   libavformat     63.1.101
   libavutil       61.1.101
   libswresample   7.1.101
   libswscale      10.1.101

Other Information

- Linux version: Manjaro Linux
- Kernel Version: 7.0.9-1-cachyos-bore
- Mesa/GPU Driver Version: OpenGL version string: 4.6 (Compatibility Profile) Mesa 26.2.2-arch1.1
- Window Manager and Version: KDE Plasma 6.7.4
- Source of mpv: repository

Reproduction Steps

The tests are commands to be copied and pasted in a console to observe the properties when opening a non-seekable file and partially seekable (thanks to the cache) stream.

Test 1 (non-seekable file):

p=/tmp/w.lua; mkfifo $p; echo 'local function h(n,v) if v ~= nil then print(n .. " changed to: " .. tostring(v)) end end; mp.observe_property("partially_seekable", "string", h); mp.observe_property("seekable", "string", h)' > $p & mpv --script=$p ealogo.vp6; rm $p

Test 2 (cache-seekable stream):

p=/tmp/w.lua; mkfifo $p; echo 'local function h(n,v) if v ~= nil then print(n .. " changed to: " .. tostring(v)) end end; mp.observe_property("partially_seekable", "string", h); mp.observe_property("seekable", "string", h)' > $p & mpv --script=$p https://9a81dd4ee3884d0dbcacafaf0d81327a.mediatailor.us-east-1.amazonaws.com/v1/master/04fd913bb278d8775298c26fdca9d9841f37601f/RakutenTV-eu_BilliardsTV/playlist.m3u8; rm $p

Expected Behavior

Test 1 (non-seekable file):

seekable changed to: no

Test 2 (cache-seekable stream):

partially_seekable changed to: yes
seekable changed to: yes

Actual Behavior

Test 1 (non-seekable file):

seekable changed to: yes

Test 2 (cache-seekable stream):

seekable changed to: no

Log File

output Test 1 (non-seekable file).txt

output Test 2 (cache-seekable stream).txt

Sample Files

ealogo.vp6.zip
(the ealogo.vp6 file should be extracted first otherwise it will be identified correctly as seekable)

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

• I tested and confirmed that the issue exists with the latest release version or newer.
• 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 running the two provided mpv observe_property reproduction commands and compare their output with the attached logs. Trace the seekable and partially_seekable property entry points in mpv's C source, then verify that non-seekable files and cache-seekable streams report the expected values in both cases.