Multi-Track Audio

Some video files have multiple audio tracks in the source material. Nomad Media handles these across three different processing stages.

Proxy Transcoding

When transcoding to a proxy, the default transcoding profile transcodes each audio track one-for-one from the source. A source with 4 audio tracks produces a proxy with 4 audio tracks.

• The proxy can be downloaded and played in a non-browser player (such as VLC) with all audio tracks visible.
• Web browsers do not support playback of more than one audio track for MP4 (progressive) files. Only the first audio track plays in the browser — this is a browser technology limitation, not a Nomad Media limitation.
• Nomad Media supports an option to consolidate all audio tracks into a single track during transcoding ("flattening"). This works well for separated audio tracks but is not suitable for multi-lingual tracks or tracks that would conflict when merged. Flattening can be scoped with rules (e.g., only flatten audio in certain folders). Contact support to enable this option.
• For true multi-track playback in a browser, see HLS/Dash below.

HLS/Dash Transcoding

When transcoding to HLS or Dash (a separate cost), each audio track is retained in the output. Web players automatically display an audio-track selector when the content is played in a browser.

For cost efficiency, a custom HLS or Dash profile can be created with a single output rendition when only one track is needed at delivery time.

Transcriptions and Subtitles

When using AI transcription, only the first audio track from the MP4 proxy is analyzed. Additional tracks are ignored.

If the audio track consolidation (flattening) feature is enabled, transcription occurs after consolidation completes.