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HLS alternate audio+subtitle tracks support ?


I'm testing Viblast Player (release 6.36) with an HLS stream having :
. 6 qualities for Adaptive Bitrate
. 2 alternate audio tracks (English and French)
. 3 alternate subtitle tracks (English, English with audio description and French)

This movie plays properly on any iOS devices and Mac OS X operating system. But Viblast Player return this error message "The video could not be loaded, either because  the server or network failed or because the format is not supported".

Here is the HLS link :

And here is my Viblast Player test page :

Do I need to setup or develop something special to play multi audio/subtitle streams with your HTML5 player ?

Best regards

Hi Beloko,

Thank you for providing us with a test stream. This helped a lot.

The reason why the stream doesn't event start playing is the fact that the video stream is not video only. It contains an audio stream (in English) but at the same time there is another external audio stream (in English or French). This makes two audio streams in total and this confuses the decoder which then simply reports an error. I am not sure why the video stream also contains a redundant audio stream. Maybe you know? We can fix this issue by dropping the unnecessary stream. But I cannot give you and ETA on this.

One more thing, Viblast does not support segmented subtitles, like the ones in HLS. This means that subtitles are not going to work even if video/audio playback works.

I will keep you posted on any new developments regarding these features.

Best Regards,


Hello Svetlin,

The main video stream embeds the prefered audio stream.
This is to preserve compatibility with old Apple devices and many current Android devices.

Because HLS's alternate media tracks capabililty appears in Draft Pantos HTTP Live Streaming N°7 :

It requires HLS version 4 for alternate audio support (09/30/2011) and HLS version 5 for alternate subtitle support (09/22/2012) :

So, it means you need at least an Apple device with iOS 6 operating system to play an HLS stream using alternate audio/subtitle.

When HLS stream contains alternate audio tracks, it overrides audio of the main video track. This is how Quicktime player works on iOS and Mac OS X.

So here is the HLS link for old compatibility :

And here is the HLS link for players with version 5 (and upper) capability :

This two links use the same video track. Then it consumes less storage on the hosting server and it offers playback for old and new HLS players at the same time.

However the HLS stream with the version 5 should be playable on any old HLS player. Because Draft Pantos says : An Attribute/value pair with an unrecognized AttributeName MUST be ignored by the client. And : Attribute/value pairs of type enumerated-string that contain unrecognized values SHOULD be ignored by the client.

I enjoy to share this sample with your dev team. Hope they'll find it helpfull and interesting for future Viblast player updates.

Best regards

 Hi Beloko,

Thank you for the detailed explanation. We suspected that it had something to do with compatibility but now it makes perfect sense.

> I enjoy to share this sample with your dev team. Hope they'll find it helpfull and interesting for future Viblast player updates.

Yes, your feedback is much appreciated. We are working on these issues and will keep you posted about new releases.



Of course Svetlin.
As always I remain attentive to your developments :)

Best regards

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