Add bounded session playback, synced audio and frame thumbnails

README.md

@@ -10,7 +10,7 @@ The recording foundation is being validated (see [docs/validation.md](docs/valid
 
 The desktop app detects Steam games, owns the recorder on a background thread, persists settings and sessions, and loads recorded sessions from disk. Linux detects Steam’s `reaper` processes and watches their pidfds; Windows reads Steam’s registry state and watches native process handles (cross-checked, not run). Game exit finalises a session; closing the window keeps the current session recording until the game exits, then exits the app. Ctrl+Q or Quit stops the output cleanly.
 
-The desktop interface follows the web Clipbin's look (zinc dark theme, purple accent, Geist Mono): a session library, a session timeline with bookmarks and a clip selection, clips, and settings. It shows sessions from disk; `CLIPBIN_SAMPLE_LIBRARY=1` fills it with example sessions for interface work. Playback, export, global hotkeys, storage cleanup, autostart and a tray are not implemented yet. After closing the only window, reopening it without a tray is a follow-up.
+The desktop interface follows the web Clipbin's look (zinc dark theme, purple accent, Geist Mono): a session library, a session timeline with bookmarks and a clip selection, clips, and settings. It shows sessions from disk; `CLIPBIN_SAMPLE_LIBRARY=1` fills it with example sessions for interface work. Playback and frame seeking work across completed segments, including active sessions and missing footage. The editor has combined audio playback, mute/volume, Space/K to play/pause and J/L or arrows to step frames. Sessions and clips use cached frame thumbnails when footage is available. Export, global hotkeys, storage cleanup, autostart and a tray are not implemented yet. After closing the only window, reopening it without a tray is a follow-up.
 
 Windows is a first-class target. Every change must keep the Windows code paths building (`cargo clippy --target x86_64-pc-windows-msvc`) and list what still needs validating on Windows.
 
@@ -19,6 +19,7 @@ Windows is a first-class target. Every change must keep the Windows code paths b
 ```text
 crates/
   clipbin-core/       Settings, Steam detection and session storage; independent of GPUI and OBS.
+  clipbin-media/      Shared FFmpeg probing, scaled video/audio playback and cached thumbnails.
   clipbin-obs/        Recording engine over the pinned libobs runtime; all unsafe code is in src/ffi.rs.
   clipbin-probe/      Validation probe for capture, encoders, segments and status.
   clipbin-desktop/    GPUI application and initial session-library view.
@@ -41,7 +42,7 @@ Keep the lockfile checked in and use `--locked`. It currently pins `libc` to 0.2
 On Arch/CachyOS, install the native build dependencies:
 
 ```sh
-sudo pacman -S --needed base-devel pkgconf fontconfig freetype2 wayland libxcb libxkbcommon libxkbcommon-x11 openssl clang
+sudo pacman -S --needed base-devel pkgconf fontconfig freetype2 wayland libxcb libxkbcommon libxkbcommon-x11 openssl clang ffmpeg alsa-lib pipewire-alsa libpulse
 ```
 
 ### OBS runtime
@@ -62,9 +63,11 @@ On Debian/Ubuntu:
 
 ```sh
 sudo apt-get update
-sudo apt-get install build-essential pkg-config libfontconfig1-dev libfreetype6-dev libwayland-dev libxcb1-dev libxkbcommon-dev libxkbcommon-x11-dev libssl-dev
+sudo apt-get install build-essential pkg-config libfontconfig1-dev libfreetype6-dev libwayland-dev libxcb1-dev libxkbcommon-dev libxkbcommon-x11-dev libssl-dev libavcodec-dev libavformat-dev libavutil-dev libswscale-dev libswresample-dev libasound2-dev libpulse-dev pipewire-alsa
 ```
 
+Media dynamically links FFmpeg through `ffmpeg-next` 9. Linux uses system FFmpeg 8. On Windows, set `FFMPEG_DIR` to an FFmpeg **7.1 shared development** package with MSVC import libraries, matching the OBS-bundled `avcodec-61`, `avformat-61`, `avutil-59`, `swscale-8` and `swresample-5` DLLs. Keep those OBS DLLs alongside the desktop executable; do not mix FFmpeg major versions. Audio uses cpal (PulseAudio or ALSA/PipeWire on Linux, WASAPI on Windows).
+
 For Windows, use the MSVC Rust toolchain and Visual Studio Build Tools with the Desktop development with C++ workload. Windows support needs validation on a Windows machine; see [docs/validation.md](docs/validation.md#windows).
 
 Run the desktop shell from an active graphical session:
@@ -87,7 +90,7 @@ cargo test --locked --workspace
 cargo clippy --locked --target x86_64-pc-windows-msvc -p clipbin-core -p clipbin-obs -p clipbin-probe --all-targets -- -D warnings
 ```
 
-Recording validation on Linux, headless: `scripts/validate/linux-rig.sh`. Automatic desktop sessions: `scripts/validate/linux-session.sh` (fake Steam reaper, recording and library screenshots, close-window survival, game exit and explicit Quit). Interface screenshots, headless: `scripts/rig/screenshot-ui.sh` (screens: sessions, session, clips, settings, failed, empty). The rig has no input devices; `rig-pointer` drives a virtual pointer (`move`, `click`, `down`/`up`, `scroll`, `sleep` on stdin) and `wtype` types. `CLIPBIN_TRACE_FRAMES=1` logs frame times.
+Recording validation on Linux, headless: `scripts/validate/linux-rig.sh`. Automatic desktop sessions: `scripts/validate/linux-session.sh` (fake Steam reaper, recording and library screenshots, close-window survival, game exit and explicit Quit). Playback fixtures: `scripts/validate/playback-fixture.sh`. Playback/audio e2e: `scripts/validate/linux-playback.sh [output-dir]` (moving preview, active recording, gaps, thumbnails, audio monitor, timing and CPU report). Fake Steam rigs must run serially because discovery reads the machine’s `/proc`. Interface screenshots, headless: `scripts/rig/screenshot-ui.sh` (screens: sessions, session, clips, settings, failed, empty). The rig has no input devices; `rig-pointer` drives a virtual pointer (`move`, `click`, `down`/`up`, `scroll`, `sleep` on stdin) and `wtype` types. `CLIPBIN_TRACE_FRAMES=1` logs frame times.
 
 Development builds optimise dependencies (`[profile.dev.package."*"]`): unoptimised GPUI made screens noticeably slow, with first frames of 200–300 ms.