a wrapper to view upscaled primary monitor natively insted of tigervnc it runs its own wrapper service to get around some errors;

cdmpv — Stabilized pipeline & troubleshooting notes (2025-12-26)

Summary

Stabilized cdmpv live-desktop capture → mpv pipeline. Root cause analysis, fix applied and operational commands have been recorded here so the environment can be reproduced or rolled back.

Work completed:

• Identified and removed an invalid mpv profile (qrawvideo) that caused immediate mpv exit and subsequent ffmpeg broken-pipe failures.
• Replaced live-desktop-mpv.sh with a simplified, robust pipeline wrapper that uses only validated ffmpeg and mpv flags and writes a small persistent run log.
• Verified the service starts via user systemd (unit: ~/.config/systemd/user/cdmpv-live.service) and confirmed mpv window appears with near real-time latency (~1s).
• Captured diagnostic outputs and patterns in the log for further tuning.

Root causes (concise)

1. mpv was passed --profile=qrawvideo which does not exist on target system — mpv immediately exited.
2. ffmpeg produced frames while mpv was gone; pipe broke and ffmpeg failed with "Broken pipe" and "Conversion failed!".
3. systemd restarted the service repeatedly, producing a restart storm.

Files changed (updated) — locations

• ~/cdmpv/live-desktop-mpv.sh — replaced with a simplified robust pipeline (this file contains the runnable pipeline and logging).

Other relevant files (unchanged but important):

• ~/cdmpv/run-cdmpv-wrapper.sh — wrapper used by the systemd unit. Keep executable.
• ~/.config/systemd/user/cdmpv-live.service — user unit that launches the wrapper.
• Log: ~/.local/state/cdmpv/live-desktop-mpv.log

How to start / stop / inspect

Start (user unit):

systemctl --user daemon-reload
systemctl --user enable --now cdmpv-live.service

Stop:

systemctl --user stop cdmpv-live.service

Reset failed state (if systemd refuses to start after crashes):

systemctl --user reset-failed cdmpv-live.service
systemctl --user restart cdmpv-live.service

Inspect logs:

journalctl --user -u cdmpv-live.service -f
# and
tail -n 400 ~/.local/state/cdmpv/live-desktop-mpv.log

Quick reproducible pipeline (manual test)

Run this to test single-monitor capture and verify offsets without the systemd unit:

# Find monitors and offsets
xrandr --listmonitors

# Example: capture a 1920x1080 region on the second monitor offset (1920,0)
ffmpeg -hide_banner -nostdin -fflags nobuffer -f x11grab -video_size 1920x1080 -framerate 30 -i :0+1920,0 -pix_fmt yuv420p -f nut - | \
  mpv --demuxer-lavf-format=nut - --no-audio --force-window=yes --keep-open=yes --untimed

If that produces the expected single-monitor view in mpv, you can map those values into live-desktop-mpv.sh by setting the HOST_DISPLAY and CAPTURE_OFFSET (or by editing the script to pass a :0+X,Y capture target).

Known issue: infinite mirror (mirroring both screens)

Cause: current pipeline captures the entire X root (:0) which on a multi-monitor X server is the combined desktop (all monitors arranged side-by-side). When mpv displays the upscaled result on the same X server, if the capture region includes the output window, you get a recursive mirror.

Mitigations (ordered):

1. Capture a single monitor (recommended). Use -video_size WxH -i :0+X,Y where X,Y are the top-left pixel of the target monitor. Use xrandr --listmonitors to obtain per-monitor geometry and offsets.

2. Create a small X screen / nested X server for capture. Use an Xvfb/Xvnc nested instance dedicated solely to the guest environment you upscale; do not render the mpv window into that same X screen.

3. Move mpv output to a different display / fullscreen overlay. Run mpv on a separate display (e.g. another virtual display or use Wayland XWayland trickery) so ffmpeg capturing :0 will not include the mpv window.

4. Filter the capture area by window id. Use ffmpeg's -i x11grab with a window ID (if stable) or extract the window geometry and capture only that box — but this is fragile if mpv moves.

Immediate recommended fix (practical):

• Edit ~/cdmpv/live-desktop-mpv.sh and set CAPTURE_TARGET=':0+X,Y' and VIDEO_SIZE='WxH' for the monitor you want to capture. Example values for a primary 1920×1080 monitor at X offset 0:

VIDEO_SIZE=1920x1080
CAPTURE_TARGET=':0+0,0'

• Or launch the manual test command above to discover correct offsets and sizes, then export those into the script or config.sh.

How to revert to previous script (git / backup)

If you had the prior copy in Git, use git checkout -- ~/cdmpv/live-desktop-mpv.sh.
If not, keep a backup before editing in future:

cp ~/cdmpv/live-desktop-mpv.sh ~/cdmpv/live-desktop-mpv.sh.bak.$(date -Is)

Diagnostics snippets collected during the run (high-value lines)

• mpv returned: Unknown profile 'qrawvideo' → fixed by removing profile.
• ffmpeg errors that followed were Error muxing a packet / Error writing trailer: Broken pipe — these were secondary to mpv exit.
• Current runtime log location: ~/.local/state/cdmpv/live-desktop-mpv.log (first lines contain detection output and pipeline command line).