How does youtube-dl detect advertisements?

[ischmidt20]

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Question

Fox Sports Go recently changed their streaming service. Previously, I used to be able to record live streams and download event replays by passing headers into streamlink. However, recording live with streamlink "works" just fine, but because commercials have some kind of different codec than the actual content, I can't do anything with the resulting .ts file.

However, I can download replays from FOX.com just fine, using a youtube-dl command like this: youtube-dl --hls-prefer-native -f 3750 https://content-auso1.uplynk.com/preplay2/6f324d0648b34576b36ce49160add428/391dec8c1a9a07b70d3062e4bf1a6e3c/4sQNPrWNbJWMzPMP2RXiNy2SFAhlIDUYbUwS2TJwN94h.m3u8?pbs=38dc148aad7c4a7f981a8dd57493a625

The big problems with this are that a) I have to wait until a replay is posted; and b) FOX is very inconsistent as to which events get replays posted and which do not, meaning I'm SOL if I'm trying to save an event that just doesn't have a replay for some reason. If I could record live, this wouldn't be an issue, but again, the commercials are throwing things off.

One of the output lines from youtube-dl is [hlsnative] Total fragments: 1815 (not including 504 ad).

So my question is: how does youtube-dl detect which segments are ads in the .m3u8 file? If I can figure that out, perhaps I can rig streamlink to ignore those segments when recording, saving me a lot of trouble.

Thanks!

[dstftw]

youtube-dl/youtube_dl/downloader/hls.py

Lines 78 to 80 in 427cc21

	def is_ad_fragment_start(s):
	return (s.startswith('#ANVATO-SEGMENT-INFO') and 'type=ad' in s
	or s.startswith('#UPLYNK-SEGMENT') and s.endswith(',ad'))