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

FFmpeg trac at avcodec.org
Thu Sep 18 01:38:06 CEST 2014

#2886: HLS source with multiple variants is not optimally handled
             Reporter:  sinkers      |                    Owner:
                 Type:  enhancement  |                   Status:  new
             Priority:  wish         |                Component:  avformat
              Version:  git-master   |               Resolution:
             Keywords:  HLS          |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |

Comment (by sinkers):

 How are you defining what are unneeded variants?

 If you like I am happy to contribute some kind of spec for this if you
 think it would help and also happy to assist with samples and testing.

 Generally the behaviour for this should be as follows:
 1. Parse the master playlist and extract all variants (including alternate
 audio and text)
 2. Start with the lowest bitrate variant
 3. Calculate what sort of bandwidth we have by measuring the download of
 the lowest variant. If the variant playlist doesn't include the bitrate
 against each stream then until the bitrates have been downloaded assume
 that they are in order e.g. lowest first
 4. As quickly as possibly move to the variant that most closely matches
 the current bandwidth
 5. Monitor the fill rate of the buffer to get an idea of current bandwidth
 and if required switch to a variant with a bandwidth closest to the
 observed bandwidth

 Note that the dash.js client isn't a bad reference on handling the
 heuristics for ABR (but not the HLS part) and probably better than the VLC
 example above, the latest version is here:
 and the code is here: https://github.com/Dash-Industry-

 For HLS parsing there is a good example (in Javascript) here:

Ticket URL: <https://trac.ffmpeg.org/ticket/2886#comment:9>
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