diff --git a/youtube_dl/downloader/external.py b/youtube_dl/downloader/external.py
index 30277dc20..8d642fc3e 100644
--- a/youtube_dl/downloader/external.py
+++ b/youtube_dl/downloader/external.py
@@ -225,7 +225,7 @@ class FFmpegFD(ExternalFD):
 
         args += ['-i', url, '-c', 'copy']
         if protocol == 'm3u8':
-            if self.params.get('hls_use_mpegts', False):
+            if self.params.get('hls_use_mpegts', False) or tmpfilename == '-':
                 args += ['-f', 'mpegts']
             else:
                 args += ['-f', 'mp4', '-bsf:a', 'aac_adtstoasc']
diff --git a/youtube_dl/postprocessor/ffmpeg.py b/youtube_dl/postprocessor/ffmpeg.py
index b64cd396b..1793a878c 100644
--- a/youtube_dl/postprocessor/ffmpeg.py
+++ b/youtube_dl/postprocessor/ffmpeg.py
@@ -175,7 +175,8 @@ class FFmpegPostProcessor(PostProcessor):
         # Always use 'file:' because the filename may contain ':' (ffmpeg
         # interprets that as a protocol) or can start with '-' (-- is broken in
         # ffmpeg, see https://ffmpeg.org/trac/ffmpeg/ticket/2127 for details)
-        return 'file:' + fn
+        # Also leave '-' intact in order not to break streaming to stdout.
+        return 'file:' + fn if fn != '-' else fn
 
 
 class FFmpegExtractAudioPP(FFmpegPostProcessor):