Bug Report

• [x ] This is a bug report and I have read the contribution guidelines.

Description

streamlink 1.0.0 on windows 10 64bit (latest updates) has a chance of playing pre-roll ads before loading the twitch stream. sometimes it will partially play the end of an ad (i.e. 1 or 2 seconds), sometimes the entire ad. sometimes the ad is low resolution (480/720), sometimes 1080p. sometimes you get expected behavior (no ads).

Expected / Actual behavior

expected: play the stream straight away
actual: sporadic pre-rolls play, then the stream.

Reproduction steps / Explicit stream URLs to test

1. use streamlink 1.0.0
2. execute streamlink using cmd line "streamlink twitch.tv/sodapoppin best"
3. other twitch streams can exhibit the same issue, but not always

Log output

C:\WINDOWS\system32>streamlink twitch.tv/sodapoppin best -l debug
[cli][info] Found matching plugin twitch for URL twitch.tv/sodapoppin
[plugin.twitch][debug] Getting live HLS streams for sodapoppin
[cli][info] Available streams: audio_only, 160p (worst), 360p, 480p, 720p, 720p60, 1080p60 (best)
[cli][info] Opening stream: 1080p60 (hls)
[cli][info] Starting player: "C:\mpv-x86_64-20190224\mpv.exe"

Additional comments, screenshots, etc.

configuration file is default save for player-passthrough enabled/default player changed to mpv.
video of the issue in action - https://mega.nz/#!HEBn1K4S!titCic2lUv4Hsz2c5LjY4TDvK2cjrHRS_Y_BbyO8COk
i'll stress that this is sporadic - sometimes i'll get an ad no matter how many times i load the stream. sometimes i won't get an ad at all. this first started happening for me on march 14th.
bonus: alternate player for twitch.tv plugin (chrome/firefox) has the same issue.

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