# Add files to an existing asset

You can add files to an asset at any point after it is created. Common reasons to add files include:

- **Adding subtitle or caption files** (`.vtt`, `.srt`): Make your content accessible with captions without re-encoding.
- **Adding additional audio tracks**: Attach alternate language dubs or audio descriptions to the same asset.
- **Uploading an original source file**: Reference the master file alongside the encoded outputs.
- **Replacing or supplementing encoded outputs**: Add a new encoded version alongside existing ones.

Files you upload are stored in the asset's cloud storage container. After uploading, MK.IO detects the new files and they appear in the asset's **Files on storage** list.

## Steps

### Open the asset

Go to **Assets** in the left navigation and click the name of the asset you want to update.

### Navigate to Files on storage

Scroll down to the **Tracks** section and select the **Files on storage** tab. This lists all files currently stored in the asset's container.

### Add files

Click **+ Add Files**. A file picker opens: you can click to browse or drag and drop files directly.

### Upload

Select your file or files and click **Upload**. MK.IO transfers the files to the asset's cloud storage container.

> **Info:** After uploading, MK.IO reflects the new files in the asset immediately. If you upload a subtitle or audio track file, you may need to create a new transform job or use the track insertion feature to attach it formally to the manifest. See [Add a track to a VOD asset](/mkio/reference/encoding-transform-presets/add-a-track-to-a-vod-asset).

## Supported file types

MK.IO accepts any file type in an asset container: the asset is a general-purpose storage container. However, only recognised media formats are processed for streaming:

- **Video**: `.mp4`, `.mov`, `.mxf`, `.ts`, and other common formats
- **Audio**: `.mp3`, `.aac`, `.wav`
- **Subtitles**: `.vtt`, `.srt`, `.ttml`
- **Manifests**: `.ism`, `.mpd`, `.m3u8` (generated by encoding jobs)

If you need to add a subtitle track to an already-encoded asset without re-encoding, see [Add a track to a VOD asset](/mkio/reference/encoding-transform-presets/add-a-track-to-a-vod-asset).