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A VOD file can contain several embedded audio tracks, so viewers can switch languages during playback. Upload one video with the original track and the alternative tracks. Gcore exposes those tracks in the built-in player and in HLS and DASH playback.
Multi-audio track selection in video player

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Source video

  • Embed all audio tracks in the uploaded MP4.
  • Assign the correct language metadata to each track.
  • Use a supported audio codec. Codec rules are in VOD source files.
During processing, Gcore extracts each audio track and writes the HLS and DASH audio representations.

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Built-in player

Multi-audio tracks are available in the Gcore built-in player and in compatible HLS and DASH players. Language selection depends on the player and the device. The demo below uses Tears of Steel HD with English original audio and Spanish, German, and Russian AI-dubbed tracks. Use the audio menu in the player to switch between them.
Player URL: https://player.gvideo.co/videos/2675_HCzdHTj79iSt3wiW

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HLS and DASH playback

A player other than the built-in player reads the same tracks from the HLS or DASH manifest.

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HLS manifest

In HLS, each audio track is an #EXT-X-MEDIA entry:
DEFAULT=YES marks the track played at startup. AUTOSELECT=YES lets a compatible player select a track from the device language settings. In this manifest, the original track is DEFAULT=YES,AUTOSELECT=YES, and the alternative tracks are DEFAULT=NO,AUTOSELECT=NO. HLS manifest: https://demo-public.gvideo.io/videos/2675_HCzdHTj79iSt3wiW/master.m3u8 Playback in hls.js:
hls.js playback with four audio tracks

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DASH manifest

In MPEG-DASH, each audio language is a separate AdaptationSet. Players can list and switch languages independently of video quality.
  • lang is the ISO language code used for language matching.
  • label is the language name shown in the player.
  • Representation sets the codec, bitrate, and sampling rate.
DASH manifest: https://demo-public.gvideo.io/videos/2675_HCzdHTj79iSt3wiW/master.mpd Playback in dash.js:
dash.js playback with four audio languages