[FFmpeg-trac] #2886(FFmpeg:new): HLS source with multiple variants is not optimally handled

[FFmpeg]

#2886: HLS source with multiple variants is not optimally handled
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             Reporter:  sinkers  |                     Type:  enhancement
               Status:  new      |                 Priority:  normal
            Component:  FFmpeg   |                  Version:  unspecified
             Keywords:  HLS      |               Blocked By:
             Blocking:           |  Reproduced by developer:  0
Analyzed by developer:  0        |
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 Currently when ffmpeg parses an HLS source it it performs a scan of all
 the available variants resulting in a very slow startup time. It also does
 not adapt to changes in network conditions to switch between the variants.

 Both of these cases are some of purposes of the HLS protocol.

 For startup the common convention with in formatting HLS master playlists
 is to make the first variant in the list the one that should be played
 first. So the reader should attempt to start playing this variant first
 without parsing all the variant playlists.

 The reader should then maintain a buffer to detect how fast it is reading
 segments in the variant playlist and if the buffer is not filling fast
 enough to maintain playback for the current bitrate it should switch to a
 lower bitrate, if the low buffer continues then the reader should switch
 to a lower rate until it is as the lowest bitrate. If the buffer is full
 for a specified period then the reader should attempt to read the next
 higher bitrate and so on until the top rate is reached.

 Note that the reader should also look at the bitrates recorded in the
 BANDWIDTH= field of the playlist as opposed to processing the segments as
 it should be assumed that the media honours the specification so as to
 reduce processing overhead and make for a faster experience.

 A reasonable sample of a master playlist with multiple bitrate variants is
 available here:
 https://devimages.apple.com.edgekey.net/streaming/examples/bipbop_4x3/bipbop_4x3_variant.m3u8

 If someone starts on this I am happy to provide more detail.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2886>
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