From 19a17d462388b5d10196352e5f9d1491d608783a Mon Sep 17 00:00:00 2001
From: Yen Chi Hsuan <yan12125@gmail.com>
Date: Sat, 5 Mar 2016 18:18:28 +0800
Subject: [PATCH 1/3] [utils] Add codec2ext

---
 youtube_dl/utils.py | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/youtube_dl/utils.py b/youtube_dl/utils.py
index 22a39a0ab..dc0bf5627 100644
--- a/youtube_dl/utils.py
+++ b/youtube_dl/utils.py
@@ -1893,6 +1893,19 @@ def mimetype2ext(mt):
     }.get(res, res)
 
 
+def codec2ext(codec):
+    codec_type = codec.split('.')[0]
+
+    # Leave the return value None for unknown values as codec_type
+    # is not a good fallback for file extensions
+    return {
+        'avc1': 'mp4',
+        'mp4a': 'm4a',
+        'vorbis': 'webm',
+        'vp9': 'webm',
+    }.get(codec_type)
+
+
 def urlhandle_detect_ext(url_handle):
     try:
         url_handle.headers

From 2def60c5f3426e4f6b7e5f0bc8a92811e5a592b9 Mon Sep 17 00:00:00 2001
From: Yen Chi Hsuan <yan12125@gmail.com>
Date: Sat, 5 Mar 2016 18:18:39 +0800
Subject: [PATCH 2/3] [common] Use codec2ext for DASH formats (#8764)

---
 youtube_dl/extractor/common.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/youtube_dl/extractor/common.py b/youtube_dl/extractor/common.py
index 07bd2cbe2..f337caf20 100644
--- a/youtube_dl/extractor/common.py
+++ b/youtube_dl/extractor/common.py
@@ -29,6 +29,7 @@ from ..utils import (
     age_restricted,
     bug_reports_message,
     clean_html,
+    codec2ext,
     compiled_regex_type,
     determine_ext,
     error_to_compat_str,
@@ -1471,6 +1472,7 @@ class InfoExtractor(object):
                         f = {
                             'format_id': '%s-%s' % (mpd_id, representation_id) if mpd_id else representation_id,
                             'url': base_url,
+                            'ext': codec2ext(representation_attrib.get('codecs')),
                             'width': int_or_none(representation_attrib.get('width')),
                             'height': int_or_none(representation_attrib.get('height')),
                             'tbr': int_or_none(representation_attrib.get('bandwidth'), 1000),

From 6d210f20905a5c31f72eff16f9f4dbbed7f52c70 Mon Sep 17 00:00:00 2001
From: Yen Chi Hsuan <yan12125@gmail.com>
Date: Sun, 6 Mar 2016 13:32:03 +0800
Subject: [PATCH 3/3] [utils] Add more codecs to codec2ext

BBC uses avc3. Here's an example (thanks to @remitamine for this example)

http://rdmedia.bbc.co.uk/dash/ondemand/bbb/2/client_manifest-common_init.mpd

See also https://trac.ffmpeg.org/ticket/5217
---
 youtube_dl/utils.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/youtube_dl/utils.py b/youtube_dl/utils.py
index dc0bf5627..0e04e91a4 100644
--- a/youtube_dl/utils.py
+++ b/youtube_dl/utils.py
@@ -1900,6 +1900,9 @@ def codec2ext(codec):
     # is not a good fallback for file extensions
     return {
         'avc1': 'mp4',
+        'avc2': 'mp4',
+        'avc3': 'mp4',
+        'avc4': 'mp4',
         'mp4a': 'm4a',
         'vorbis': 'webm',
         'vp9': 'webm',