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