screenshare: honor viewer settings for the VLC player too

The viewer playback settings (hardware decode + buffering) only shaped
mpv's argv; vlc_args() was fixed, so a VLC viewer silently ignored them.
The load-bearing case is hardware decode: mpv defaults to software decode
(the A-bug fix), but VLC hardware-decodes by default, so a VLC viewer with
the default hardware_decode=false still got GPU decode and could hit the
frame-1 freeze the default exists to avoid — the toggle did nothing.

vlc_args() now takes the settings and maps the knobs that translate
cleanly to VLC: hardware decode (--avcodec-hw=none/any) and buffering
posture (network/live caching ms). The genuinely mpv-specific knobs
(cache_mb byte-cache, extra_mpv_args) stay mpv-only; the Settings UI
hints are reworded to say which knobs are mpv-only vs universal. +2 tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/mod.rs

@@ -3452,7 +3452,7 @@ fn share_player_hint(player: SharePlayer) -> &'static str {
 fn share_buffering_hint(buffering: ShareBuffering) -> &'static str {
     match buffering {
         ShareBuffering::LowLatency => "Small buffers for interactive screen sharing.",
-        ShareBuffering::Smooth => "Larger mpv cache/readahead for steadier playback.",
+        ShareBuffering::Smooth => "Larger cache/readahead for steadier playback.",
     }
 }
 
@@ -5146,13 +5146,13 @@ fn view(state: &AppState) -> Element<'_, AppMessage> {
                             Some(screen_share.cache_mb),
                             AppMessage::ScreenShareCacheMbSelected,
                         ).width(iced::Length::Fill),
-                        text("Used as mpv demuxer cache size.").size(11).color(color_subtext),
+                        text("mpv demuxer cache size (mpv only).").size(11).color(color_subtext),
                     ].spacing(4).width(iced::Length::Fill),
                     column![
                         checkbox(screen_share.hardware_decode)
                             .label("Hardware video decode")
                             .on_toggle(AppMessage::ToggleScreenShareHardwareDecode),
-                        text("Adds --hwdec=auto to mpv. Off avoids the known frame-freeze bug.").size(11).color(color_subtext),
+                        text("GPU decode (mpv --hwdec=auto / VLC hardware decode). Off avoids the known frame-freeze bug.").size(11).color(color_subtext),
                     ].spacing(8).width(iced::Length::Fill),
                 ].spacing(16).width(iced::Length::Fill),
             ].spacing(10).width(iced::Length::Fill),

src/screenshare/mod.rs

@@ -608,7 +608,7 @@ fn event_for_log(ev: &PixelpassEvent) -> String {
 /// kept playing.
 fn launch_player(url: &str, settings: &ScreenShareSettings) -> std::io::Result<()> {
     let mpv_args = mpv_args(settings);
-    let vlc_args = vlc_args();
+    let vlc_args = vlc_args(settings);
     let first = match settings.player {
         SharePlayer::Mpv => ("mpv", &mpv_args),
         SharePlayer::Vlc => ("vlc", &vlc_args),
@@ -655,10 +655,33 @@ pub fn mpv_args(settings: &ScreenShareSettings) -> Vec<String> {
     args
 }
 
-fn vlc_args() -> Vec<String> {
+/// Build the argv for a VLC viewer. VLC honors the subset of viewer settings
+/// that map cleanly onto its option set: the buffering posture (network/live
+/// caching, in ms) and hardware decoding. The rest of the viewer knobs are
+/// mpv-specific — `cache_mb` is an mpv demuxer *byte* cache (VLC's caching is
+/// time-based, already covered by `buffering`) and `extra_mpv_args` is literally
+/// mpv flags — so they are deliberately not mapped here; the Settings UI labels
+/// them as mpv-only. Pure: no I/O.
+///
+/// The hardware-decode mapping is the load-bearing one: VLC hardware-decodes by
+/// default, so without an explicit `--avcodec-hw=none` a VLC viewer would ignore
+/// the (default-off) hardware-decode toggle and could hit the frame-1 freeze
+/// that default exists to avoid — the same A-bug that made us drop mpv's forced
+/// `--hwdec=auto`.
+fn vlc_args(settings: &ScreenShareSettings) -> Vec<String> {
+    let caching_ms = match settings.buffering {
+        ShareBuffering::LowLatency => 200,
+        ShareBuffering::Smooth => 1500,
+    };
+    let hw = if settings.hardware_decode {
+        "--avcodec-hw=any"
+    } else {
+        "--avcodec-hw=none"
+    };
     vec![
-        "--network-caching=200".to_string(),
+        format!("--network-caching={caching_ms}"),
-        "--live-caching=200".to_string(),
+        format!("--live-caching={caching_ms}"),
+        hw.to_string(),
     ]
 }
 
@@ -820,6 +843,44 @@ mod tests {
         );
     }
 
+    #[test]
+    fn vlc_args_default_disables_hardware_decode() {
+        // The A-bug fix default (hardware_decode = false) must reach VLC too:
+        // VLC hardware-decodes by default, so without an explicit
+        // `--avcodec-hw=none` a VLC viewer would ignore the toggle and could hit
+        // the frame-1 freeze. Low-latency buffering keeps the 200 ms caches.
+        assert_eq!(
+            vlc_args(&ScreenShareSettings::default()),
+            vec![
+                "--network-caching=200",
+                "--live-caching=200",
+                "--avcodec-hw=none",
+            ]
+        );
+    }
+
+    #[test]
+    fn vlc_args_smooth_buffering_and_hwdecode() {
+        // Enabling hardware decode flips VLC to `--avcodec-hw=any`; Smooth
+        // buffering raises the network/live caches. cache_mb / extra_mpv_args are
+        // mpv-only and must NOT leak into the VLC argv.
+        let settings = ScreenShareSettings {
+            hardware_decode: true,
+            buffering: ShareBuffering::Smooth,
+            cache_mb: 16,
+            extra_mpv_args: "--no-osc".to_string(),
+            ..ScreenShareSettings::default()
+        };
+        assert_eq!(
+            vlc_args(&settings),
+            vec![
+                "--network-caching=1500",
+                "--live-caching=1500",
+                "--avcodec-hw=any",
+            ]
+        );
+    }
+
     #[test]
     fn sanitize_app_name_trims_and_rejects_garbage() {
         assert_eq!(