diff --git a/imgui.ini b/imgui.ini
index b71d071..b8903b8 100644
--- a/imgui.ini
+++ b/imgui.ini
@@ -14,7 +14,7 @@ Size=200,200
 Collapsed=0
 
 [Window][Connection]
-Pos=250,275
+Pos=475,529
 Size=640,352
 Collapsed=0
 
diff --git a/internal/playback/session_command.go b/internal/playback/session_command.go
new file mode 100644
index 0000000..38f0b5d
--- /dev/null
+++ b/internal/playback/session_command.go
@@ -0,0 +1,110 @@
+package playback
+
+import (
+	"errors"
+	"fmt"
+)
+
+type SessionCommandKind uint8
+
+const (
+	CommandSetVideo SessionCommandKind = iota + 1
+	CommandSetAudio
+	CommandStopVideo
+	CommandStopAudio
+	CommandStopAll
+	CommandResumeVideo
+	CommandResumeAudio
+	CommandResumeAll
+	CommandRemoveVideo
+	CommandRemoveAudio
+	CommandEnableSync
+	CommandDisableSync
+)
+
+type SessionCommand struct {
+	Kind   SessionCommandKind
+	Config FeedConfig // Used only by SetVideo and SetAudio.
+}
+
+var (
+	ErrUnknownSessionCommand = errors.New("unknown session command")
+	ErrVideoNotConfigured    = errors.New("video feed is not configured")
+	ErrAudioNotConfigured    = errors.New("audio feed is not configured")
+)
+
+func ApplySessionCommand(
+	current SessionConfig,
+	command SessionCommand,
+) (SessionConfig, error) {
+	next := current
+	switch command.Kind {
+	case CommandSetVideo:
+		if !command.Config.IsConfigured() {
+			return current, ErrVideoNotConfigured
+		}
+		if err := command.Config.Validate(); err != nil {
+			return current, fmt.Errorf("validate video command: %w", err)
+		}
+		next.Video = command.Config
+
+	case CommandSetAudio:
+		if !command.Config.IsConfigured() {
+			return current, ErrAudioNotConfigured
+		}
+		if err := command.Config.Validate(); err != nil {
+			return current, fmt.Errorf("validate audio command: %w", err)
+		}
+		next.Audio = command.Config
+
+	case CommandStopVideo:
+		next.Video.Active = false
+		next.SyncRequested = false
+
+	case CommandStopAudio:
+		next.Audio.Active = false
+		next.SyncRequested = false
+
+	case CommandStopAll:
+		next.Video.Active = false
+		next.Audio.Active = false
+
+	case CommandResumeVideo:
+		if !next.Video.IsConfigured() {
+			return current, ErrVideoNotConfigured
+		}
+		next.Video.Active = true
+
+	case CommandResumeAudio:
+		if !next.Audio.IsConfigured() {
+			return current, ErrAudioNotConfigured
+		}
+		next.Audio.Active = true
+
+	case CommandResumeAll:
+		next.Video.Active = next.Video.IsConfigured()
+		next.Audio.Active = next.Audio.IsConfigured()
+
+	case CommandRemoveVideo:
+		next.Video = FeedConfig{}
+		next.SyncRequested = false
+
+	case CommandRemoveAudio:
+		next.Audio = FeedConfig{}
+		next.SyncRequested = false
+
+	case CommandEnableSync:
+		next.SyncRequested = true
+
+	case CommandDisableSync:
+		next.SyncRequested = false
+
+	default:
+		return current, ErrUnknownSessionCommand
+	}
+
+	if err := next.Validate(); err != nil {
+		return current, fmt.Errorf("validate desired session: %w", err)
+	}
+	return next, nil
+}
diff --git a/internal/playback/session_command_test.go b/internal/playback/session_command_test.go
new file mode 100644
index 0000000..a5bf098
--- /dev/null
+++ b/internal/playback/session_command_test.go
@@ -0,0 +1,185 @@
+package playback
+
+import (
+	"errors"
+	"testing"
+	"time"
+)
+
+func validCommandSession() SessionConfig {
+	return SessionConfig{
+		Video:         FeedConfig{Domain: "/video", UUID: "video", Active: true},
+		Audio:         FeedConfig{Domain: "/audio", UUID: "audio", Active: true},
+		SyncRequested: true,
+		Retry: RetryPolicy{
+			MaxAttempts:  3,
+			InitialDelay: time.Millisecond,
+			MaxDelay:     time.Second,
+		},
+	}
+}
+
+func TestApplySessionCommand(t *testing.T) {
+	base := validCommandSession()
+	newVideo := FeedConfig{Domain: "/new-video", UUID: "new-video", Active: false}
+	newAudio := FeedConfig{Domain: "/new-audio", UUID: "new-audio", Active: true}
+
+	tests := []struct {
+		name    string
+		current SessionConfig
+		command SessionCommand
+		want    SessionConfig
+	}{
+		{
+			name:    "set video replaces complete config",
+			current: base,
+			command: SessionCommand{Kind: CommandSetVideo, Config: newVideo},
+			want:    func() SessionConfig { c := base; c.Video = newVideo; return c }(),
+		},
+		{
+			name:    "set audio replaces complete config",
+			current: base,
+			command: SessionCommand{Kind: CommandSetAudio, Config: newAudio},
+			want:    func() SessionConfig { c := base; c.Audio = newAudio; return c }(),
+		},
+		{
+			name:    "stop video disables sync",
+			current: base,
+			command: SessionCommand{Kind: CommandStopVideo},
+			want:    func() SessionConfig { c := base; c.Video.Active = false; c.SyncRequested = false; return c }(),
+		},
+		{
+			name:    "stop audio disables sync",
+			current: base,
+			command: SessionCommand{Kind: CommandStopAudio},
+			want:    func() SessionConfig { c := base; c.Audio.Active = false; c.SyncRequested = false; return c }(),
+		},
+		{
+			name:    "stop all preserves sync request",
+			current: base,
+			command: SessionCommand{Kind: CommandStopAll},
+			want:    func() SessionConfig { c := base; c.Video.Active = false; c.Audio.Active = false; return c }(),
+		},
+		{
+			name:    "resume video",
+			current: func() SessionConfig { c := base; c.Video.Active = false; return c }(),
+			command: SessionCommand{Kind: CommandResumeVideo},
+			want:    base,
+		},
+		{
+			name:    "resume audio",
+			current: func() SessionConfig { c := base; c.Audio.Active = false; return c }(),
+			command: SessionCommand{Kind: CommandResumeAudio},
+			want:    base,
+		},
+		{
+			name:    "resume all activates only configured feeds",
+			current: func() SessionConfig { c := base; c.Video.Active = false; c.Audio = FeedConfig{}; return c }(),
+			command: SessionCommand{Kind: CommandResumeAll},
+			want:    func() SessionConfig { c := base; c.Audio = FeedConfig{}; return c }(),
+		},
+		{
+			name:    "remove video clears config and disables sync",
+			current: base,
+			command: SessionCommand{Kind: CommandRemoveVideo},
+			want:    func() SessionConfig { c := base; c.Video = FeedConfig{}; c.SyncRequested = false; return c }(),
+		},
+		{
+			name:    "remove audio clears config and disables sync",
+			current: base,
+			command: SessionCommand{Kind: CommandRemoveAudio},
+			want:    func() SessionConfig { c := base; c.Audio = FeedConfig{}; c.SyncRequested = false; return c }(),
+		},
+		{
+			name: "enable sync without feeds records request",
+			current: func() SessionConfig {
+				c := base
+				c.Video = FeedConfig{}
+				c.Audio = FeedConfig{}
+				c.SyncRequested = false
+				return c
+			}(),
+			command: SessionCommand{Kind: CommandEnableSync},
+			want: func() SessionConfig {
+				c := base
+				c.Video = FeedConfig{}
+				c.Audio = FeedConfig{}
+				c.SyncRequested = true
+				return c
+			}(),
+		},
+		{
+			name:    "disable sync",
+			current: base,
+			command: SessionCommand{Kind: CommandDisableSync},
+			want:    func() SessionConfig { c := base; c.SyncRequested = false; return c }(),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ApplySessionCommand(tt.current, tt.command)
+			if err != nil {
+				t.Fatalf("ApplySessionCommand() error = %v", err)
+			}
+			if got != tt.want {
+				t.Fatalf("ApplySessionCommand() = %#v, want %#v", got, tt.want)
+			}
+			if got.Retry != tt.current.Retry {
+				t.Fatalf("retry changed from %#v to %#v", tt.current.Retry, got.Retry)
+			}
+		})
+	}
+}
+
+func TestApplySessionCommandFailurePreservesState(t *testing.T) {
+	base := validCommandSession()
+	tests := []struct {
+		name    string
+		current SessionConfig
+		command SessionCommand
+		wantErr error
+	}{
+		{"set empty video", base, SessionCommand{Kind: CommandSetVideo}, ErrVideoNotConfigured},
+		{"set empty audio", base, SessionCommand{Kind: CommandSetAudio}, ErrAudioNotConfigured},
+		{"invalid video", base, SessionCommand{Kind: CommandSetVideo, Config: FeedConfig{UUID: "video"}}, ErrFeedDomainRequired},
+		{"invalid audio", base, SessionCommand{Kind: CommandSetAudio, Config: FeedConfig{UUID: "audio"}}, ErrFeedDomainRequired},
+		{
+			"resume missing video",
+			func() SessionConfig { c := base; c.Video = FeedConfig{}; return c }(),
+			SessionCommand{Kind: CommandResumeVideo},
+			ErrVideoNotConfigured,
+		},
+		{
+			"resume missing audio",
+			func() SessionConfig { c := base; c.Audio = FeedConfig{}; return c }(),
+			SessionCommand{Kind: CommandResumeAudio},
+			ErrAudioNotConfigured,
+		},
+		{"unknown command", base, SessionCommand{Kind: 255}, ErrUnknownSessionCommand},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ApplySessionCommand(tt.current, tt.command)
+			if !errors.Is(err, tt.wantErr) {
+				t.Fatalf("ApplySessionCommand() error = %v, want %v", err, tt.wantErr)
+			}
+			if got != tt.current {
+				t.Fatalf("failed command changed state from %#v to %#v", tt.current, got)
+			}
+		})
+	}
+}
+
+func TestApplySessionCommandRejectsInvalidResult(t *testing.T) {
+	current := validCommandSession()
+	current.Retry = RetryPolicy{}
+	got, err := ApplySessionCommand(current, SessionCommand{Kind: CommandDisableSync})
+	if !errors.Is(err, ErrInvalidRetryDelay) {
+		t.Fatalf("ApplySessionCommand() error = %v, want %v", err, ErrInvalidRetryDelay)
+	}
+	if got != current {
+		t.Fatalf("failed command changed state from %#v to %#v", current, got)
+	}
+}