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I am using LibVlcSharp to play an adaptive video stream (HLS) transcoded by Azure Media Services with the EncoderNamedPreset.AdaptiveStreaming setting in my Xamarin.Forms app.

When viewing my video I notice that the first few (5-6) seconds of my video are very blurry.

This is probably because the player starts with a "safe" low bitrate, and after a few chunks of data have been downloaded, it determines that the bandwith is sufficient for a higher quality video being displayed and it can switch up in quality.

This first few seconds of low quality bother me, and I would rather have it start at a higher bitrate.

I would be happy if the video would switch up sooner (<2 seconds), which would probably mean I need a different encoder setting that produces smaller "chunks" of video.

But maybe the easier solution is to set the starting bitrate to a higher value.

I have seen this done on other media players in the form of ams.InitialBitrate = ams.AvailableBitrates.Max<uint>();

Does LibVlc have a similar option?

Sjors Miltenburg
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1 Answers1

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This is probably because the player starts with a "safe" low bitrate, and after a few chunks of data have been downloaded, it determines that the bandwith is sufficient for a higher quality video being displayed and it can switch up in quality.

Probably. You could verify that assumption by checking the bitrate at the start at the video and again when the quality improved, like this:

await media.Parse(MediaParseOptions.ParseNetwork);

foreach(var track in media.Tracks)
{
    Debug.WriteLine($"{nameof(track.Bitrate)}: {track.Bitrate}");
}

Does LibVlc have a similar option?

Try this

  --adaptive-logic={,predictive,nearoptimal,rate,fixedrate,lowest,highest} 
                                 Adaptive Logic

You can try it like new LibVLC("--adaptive-logic=highest")

See the docs for more info, or the forums. If that does not work, I'd set it server-side.

mfkl
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  • the --adaptive-logic=highest fixed my problem, but maybe introduced another (since it might force the highest stream on you whatever your bandwith, cancelling out the -adaptive- aspact of the video. I didn't find a good explanation of the meaning of all the options. Also I don't get what you mean by setting it server side since vlc is not active on the server. – Sjors Miltenburg Feb 16 '21 at 11:48
  • I'm not familiar with Azure Media Services but maybe this is an option? https://learn.microsoft.com/en-us/dotnet/api/microsoft.azure.management.media.models.firstquality.bitrate – mfkl Feb 17 '21 at 02:03