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[extractor/common] Clarify rationale on media playlist detection

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This commit is contained in:
Sergey M․ 2016-02-27 07:01:11 +06:00
parent fbb6edd298
commit 9cdffeeb3f
1 changed files with 15 additions and 5 deletions
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20
youtube_dl/extractor/common.py
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@ -1033,11 +1033,21 @@ class InfoExtractor(object):
return []
m3u8_doc, urlh = res
m3u8_url = urlh.geturl()
# A Media Playlist Tag MUST NOT appear in a Master Playlist
# https://tools.ietf.org/html/draft-pantos-http-live-streaming-17#section-4.3.3
# The EXT-X-TARGETDURATION tag is REQUIRED for every M3U8 Media Playlists
# https://tools.ietf.org/html/draft-pantos-http-live-streaming-17#section-4.3.3.1
if '#EXT-X-TARGETDURATION' in m3u8_doc:
# We should try extracting formats only from master playlists [1], i.e.
# playlists that describe available qualities. On the other hand media
# playlists [2] should be returned as is since they contain just the media
# without qualities renditions.
# Fortunately, master playlist can be easily distinguished from media
# playlist based on particular tags availability. As of [1, 2] master
# playlist tags MUST NOT appear in a media playist and vice versa.
# As of [3] #EXT-X-TARGETDURATION tag is REQUIRED for every media playlist
# and MUST NOT appear in master playlist thus we can clearly detect media
# playlist with this criterion.
# 1. https://tools.ietf.org/html/draft-pantos-http-live-streaming-17#section-4.3.4
# 2. https://tools.ietf.org/html/draft-pantos-http-live-streaming-17#section-4.3.3
# 3. https://tools.ietf.org/html/draft-pantos-http-live-streaming-17#section-4.3.3.1
if '#EXT-X-TARGETDURATION' in m3u8_doc: # media playlist, return as is
return [{
'url': m3u8_url,
'format_id': m3u8_id,