diff --git a/internal/adapters/audio/ffmpeg.go b/internal/adapters/audio/ffmpeg.go
index a78908a..b3e0051 100644
--- a/internal/adapters/audio/ffmpeg.go
+++ b/internal/adapters/audio/ffmpeg.go
@@ -47,11 +47,15 @@ func (f *FFmpeg) ToWAV(ctx context.Context, src, dst string) error {
 	args = append(args, "-f", "wav", dst)
 	cmd := exec.CommandContext(ctx, bin, args...)
 	cmd.WaitDelay = killGrace
-	if out, err := cmd.CombinedOutput(); err != nil {
+	// Only a bounded head of ffmpeg's output is kept: a hostile file made it print ~0.4
+	// bytes per input byte, all of which CombinedOutput would buffer and copy (#49).
+	out := &headWriter{max: maxStderr}
+	cmd.Stdout, cmd.Stderr = out, out
+	if err := cmd.Run(); err != nil {
 		if ctxErr := ctx.Err(); ctxErr != nil {
 			return fmt.Errorf("audio: ffmpeg: %w", ctxErr)
 		}
-		return fmt.Errorf("audio: ffmpeg: %w: %s", err, strings.TrimSpace(string(out)))
+		return fmt.Errorf("audio: ffmpeg: %w: %s", err, strings.TrimSpace(out.buf.String()))
 	}
 	// A zero exit that wrote nothing is still a failure: never hand whisper a
 	// missing file and let the error surface three layers later.