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• HLS audio stream choppy in iOS and Mac Safari - but ok in Chrome, VLC

  30 April 2024, by Elliot

  I have an HLS stream that seems to have the audio cut out and then return randomly. This only occurs on iOS devices, and Safari on Mac OS. It works fine on Desktop VLC, but not iOS VLC (as in, the audio never cuts out).

  


  More confusing still - if we have multiple developers listening to the same HLS stream on different devices at the same time, we all hear the audio cut out and the return at the same time. So clearly something is wrong with the stream itself.

  


  We create a dash stream from FFMPEG, and then create an HLS manifest in parallel.

  


     transcoder
            // Right now this is the max we'll get
            .audioBitrate('64k')
            // We only have 1 channel
            .audioChannels(1)
            // Enable experimental features ldash/lhls
            .outputOption('-strict', 'experimental')
            // Set url for syncing UTC timestamps with client
            .outputOption('-utc_timing_url', 'https://time.akamai.com/?iso')
            .outputOption('-write_prft', '1')
            // Streaming mode
            .outputOption('-streaming', '1')
            // Use segment file template so we dont list all segments in the manifest
            .outputOption('-use_template', '1')
            // Must be disabled for index_correction which is suggested for streaming use case
            .outputOption('-use_timeline', '0')
            // Fix up segment indexes if they drift due to bandwidth changes
            .outputOption('-index_correction', '1')
            //  Use 6 second segments, for live this shouldn't matter but this is Apple's suggested
            //  value for HLS
            .outputOption('-seg_duration', '6')
            // Push the frames out as fast as they come in
            .outputOption('-frag_type', 'every_frame')
            // Use mp4 segments
            .outputOption('-dash_segment_type', 'mp4')
            // Enabled low-latency mode
            .outputOption('-ldash', '1')
            // Output an HLS playlist too
            .outputOption('-hls_playlist', this.options.hlsEnabled ? '1' : '0')
            // HLS manifest name
            .outputOption('-hls_master_name', 'index.m3u8')
            // Use persistent HTTP connection
            .outputOption('-http_persistent', '1')
            // Do PUTs to the upload endpoint
            .outputOption('-method', 'PUT')
            // Dont let an output error hold up the stream
            .outputOption('-ignore_io_errors', '1')
            // Set a timeout for output
            .outputOption('-timeout', '1')
            // DASH format
            .format('dash');


  


  Does anyone have any suggestions for what we should dig into next?

  


• dashenc: Use pts for MPD timeline timestamps

  17 November 2014, by Martin Storsjö

  dashenc: Use pts for MPD timeline timestamps
  This should be more correct. This also should give more sensible
  
  switching between video streams with different amount of b-frame
  
  delay.
  The current dash.js release (1.2.0) fails to start playback of
  
  such files from the start (if the start pts is > 0), but this has
  
  been fixed in the current git version of dash.js.
  Also enable the use of edit lists, so that streams in many cases
  
  start at pts=0.
  Signed-off-by: Martin Storsjö <martin@martin.st>
  

  • [DBH] libavformat/dashenc.c

• avformat/dashdec: Ensure strings are zero-terminated

  2 March 2021, by Andreas Rheinhardt

  avformat/dashdec: Ensure strings are zero-terminated
  strncpy only ensures that one does not write beyond the end of the
  
  destination buffer; in case of truncation it does not zero-terminate
  
  the destination buffer. This makes using it the way it is now in the
  
  DASH demuxer dangerous. So use av_strlcpy instead.
  Also don't write anything if there is no id: The buffer has already been
  
  zeroed initially.
  The DASH testset from the Universität Klagenfurt contains samples with
  
  ids that are too long. E.g.
  
  http://ftp.itec.aau.at/datasets/DASHDataset2014/TearsOfSteel/1sec/TearsOfSteel_1s_simple_2014_05_09.mpd
  Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
  
  Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavformat/dashdec.c