diff --git a/src/render/ffmpeg.rs b/src/render/ffmpeg.rs
index 00597ca..c5557d7 100644
--- a/src/render/ffmpeg.rs
+++ b/src/render/ffmpeg.rs
@@ -92,7 +92,10 @@ impl FfmpegOutput {
 	}
 
 	pub(crate) fn enable_faststart(mut self) -> Self {
-		self.faststart = true;
+		// only enable faststart for MP4 containers
+		if matches!(self.format, FfmpegOutputFormat::AvcAac) {
+			self.faststart = true;
+		}
 		self
 	}
 
@@ -127,7 +130,7 @@ impl FfmpegOutput {
 		});
 		if let Some(ba) = self.audio_bitrate {
 			cmd.arg("-b:a").arg(ba.to_string());
-		} else {
+		} else if !matches!(self.format, FfmpegOutputFormat::Av1Flac) {
 			cmd.arg("-b:a").arg("128k");
 		}