fix: omit -t flag when duration=0; use SIGINT for graceful stop

Sources/StreamRecorderKit/FFmpegRecorder.swift

@@ -21,6 +21,7 @@ public final class FFmpegRecorder: StreamRecorderEngine {
     
     private var process: Process?
     private var duration: Double = 0
+    private var stopRequested = false
     
     public init() {}
     
@@ -46,14 +47,20 @@ public final class FFmpegRecorder: StreamRecorderEngine {
         // 启动 ffmpeg 进程
         let proc = Process()
         proc.executableURL = URL(fileURLWithPath: ffmpegPath)
-        proc.arguments = [
+        var args = [
             "-y",
             "-i", resolvedURL.absoluteString,
-            "-t", String(duration),
+        ]
+        // duration=0 表示无限录制，不传 -t 参数
+        if duration > 0 {
+            args += ["-t", String(duration)]
+        }
+        args += [
             "-c", "copy",
             "-movflags", "+faststart",
             outputPath
         ]
+        proc.arguments = args
         
         let stderrPipe = Pipe()
         proc.standardError = stderrPipe
@@ -102,7 +109,7 @@ public final class FFmpegRecorder: StreamRecorderEngine {
         stderrPipe.fileHandleForReading.readabilityHandler = nil
         isRecording = false
         
-        guard proc.terminationStatus == 0 else {
+        guard proc.terminationStatus == 0 || stopRequested else {
             throw RecordingError.processFailed(Int(proc.terminationStatus))
         }
         
@@ -117,7 +124,11 @@ public final class FFmpegRecorder: StreamRecorderEngine {
     }
     
     public func stop() {
-        process?.terminate()
+        stopRequested = true
+        // 发送 SIGINT (Ctrl+C) 让 ffmpeg 优雅关闭并写出文件头
+        if let pid = process?.processIdentifier {
+            kill(pid, SIGINT)
+        }
         isRecording = false
     }