| 1 | # Adaptive Switching Behavior
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| 2 | The HLS tech tries to ensure the highest-quality viewing experience
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| 3 | possible, given the available bandwidth and encodings. This doesn't
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| 4 | always mean using the highest-bitrate rendition available-- if the player
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| 5 | is 300px by 150px, it would be a big waste of bandwidth to download a 4k
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| 6 | stream. By default, the player attempts to load the highest-bitrate
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| 7 | variant that is less than the most recently detected segment bandwidth,
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| 8 | with one condition: if there are multiple variants with dimensions greater
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| 9 | than the current player size, it will only switch up one size greater
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| 10 | than the current player size.
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| 11 |
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| 12 | If you're the visual type, the whole process is illustrated
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| 13 | below. Whenever a new segment is downloaded, we calculate the download
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| 14 | bitrate based on the size of the segment and the time it took to
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| 15 | download:
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| 16 |
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| 17 | 
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| 18 |
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| 19 | First, we filter out all the renditions that have a higher bitrate
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| 20 | than the new measurement:
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| 21 |
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| 22 | 
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| 23 |
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| 24 | Then we get rid of any renditions that are bigger than the current
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| 25 | player dimensions:
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| 26 |
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| 27 | 
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| 28 |
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| 29 | We don't want to signficant quality drop just because your player is
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| 30 | one pixel too small, so we add back in the next highest
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| 31 | resolution. The highest bitrate rendition that remains is the one that
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| 32 | gets used:
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| 33 |
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| 34 | 
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| 35 |
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| 36 | If it turns out no rendition is acceptable based on the filtering
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| 37 | described above, the first encoding listed in the master playlist will
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| 38 | be used.
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| 39 |
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| 40 | If you'd like your player to use a different set of priorities, it's
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| 41 | possible to completely replace the rendition selection logic. For
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| 42 | instance, you could always choose the most appropriate rendition by
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| 43 | resolution, even though this might mean more stalls during playback.
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| 44 | See the documentation on `player.vhs.selectPlaylist` for more details.
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