Audio Mark

Overlays a standalone audio file — background music or a voiceover — over a video. Point audio-mark at a remote audio file and Imgix fetches it, windows it, fades it, and either mixes it under the original soundtrack or replaces it entirely.

audio-mark accepts an absolute URL or a path relative to audio-mark-base.

soundtrack is a friendly alias. Every audio-mark* parameter also accepts the soundtrack* spelling — soundtrack=music.mp3, soundtrack-volume=0.4, soundtrack[1], etc. Both forms normalize to one canonical name before rendering and caching, so they share a cache entry.

Layering

Up to 4 layers are supported. The bare audio-mark parameter is layer 0. Add audio-mark[1], audio-mark[2], and audio-mark[3] for additional layers. A layer with no resolved URL is silently dropped. Every per-layer parameter accepts the same [N] suffix: audio-mark-volume[1], audio-mark-fade-in[2], etc.

Every URL-valued parameter has a Base64 twin (audio-mark64, audio-mark64[1]) for URLs that contain reserved characters.

Scope

Audio overlays apply to MP4, HLS/DASH, and audio-only outputs (fm=m4a/mp3/wav). They are ignored where there is no audio path — GIF, still thumbnails, spritesheets, preview, and VTT.

Adding audio-mark to a source with no audio track synthesizes a silent bed and mixes the overlay onto it, so the output gains an audio track.

Render trigger. audio-mark alone does not trigger a render — also pass fm=mp4, fm=hls, fm=dash, or an audio-only fm=m4a/mp3/wav.

Soft failure

An audio-mark URL that fails to fetch, exceeds the size cap, or is not an audio file simply drops that layer and the render proceeds. In replace mode (audio-mark-mode=replace), if the only overlay drops, the original audio is kept.