The terms `#EXTM3U` and `#EXTINF:-1` are related to M3U files, which are a type of playlist file commonly used for multimedia files such as audio or video.

### 1. `#EXTM3U`
This is a required header for an M3U playlist file. The line `#EXTM3U` at the beginning of the file indicates that the file is in the Extended M3U format. The "extended" version allows for additional information such as metadata (e.g., track length, artist name) to be included in the playlist, unlike the simpler M3U format which only contains file paths.

- **Purpose**: This line tells the media player or software that the file is an Extended M3U playlist.
- **Usage**: It should appear at the very beginning of the playlist file.

Example:
```plaintext
#EXTM3U
```

### 2. `#EXTINF:-1`
The `#EXTINF` tag provides metadata about the media file that follows it in the playlist. This tag is followed by the duration of the media file in seconds and optionally, additional descriptive information such as the title or artist.

- **The `-1` value**: If `-1` is used in the `#EXTINF` tag, it signifies that the duration of the media file is unknown or undefined. This is often used for streaming media (e.g., live streams), where the duration cannot be predetermined.
  
The format for `#EXTINF` is as follows:
```
#EXTINF:duration, title
```

If the media file has an unknown or infinite duration (such as a live stream), the `duration` is set to `-1`. The `title` part is optional but often used to provide information about the media.

Example:
```plaintext
#EXTINF:-1, Live Stream Radio
http://example.com/live_stream.mp3
```

In this example:
- `#EXTINF:-1` tells the player that the media has an unknown duration (like a live stream).
- `Live Stream Radio` is the descriptive title.
- The URL or file path (`http://example.com/live_stream.mp3`) follows.

### How They Work Together:
When a media player reads an M3U playlist, it first sees the `#EXTM3U` tag, indicating that the file is an Extended M3U playlist. Then, for each media entry, the player reads the `#EXTINF` tag, which provides metadata about the file, such as its duration and title. After that, the player loads and plays the actual media file or stream listed after the `#EXTINF` entry.

In summary:
- `#EXTM3U` marks the playlist as an Extended M3U format.
- `#EXTINF:-1` indicates that the media file or stream has an unknown or indefinite duration.