Streams and Tracks
A media track is a separately described sequence of video, audio, subtitles, or other data within a media source.
Here is a possible track list for one film:
| Track in the file | Contents | Selected for this viewing? |
|---|---|---|
| Video | The film's picture | Yes |
| Audio 1 | English 5.1 soundtrack | Yes |
| Audio 2 | German stereo soundtrack | No |
| Audio 3 | English commentary | No |
| Subtitle 1 | English dialogue subtitles | Optional |
Each track is a separately described sequence. The picture can be paired with any of the soundtracks because their timestamps refer to the same presentation. Switching languages chooses another audio sequence; it does not require another copy of the video.
Stream often means the same component when discussing a file. It emphasizes the sequence of packets extracted from that track. A “network stream” can instead mean the whole delivery, including a container holding several such components.
What is inside an audio track?
The English 5.1 track contains six audio channels: five main speaker roles and a low-frequency effects channel. A channel describes one component of the sound being decoded together. It is not a separately selectable soundtrack.
At a sample rate of 48 kHz, one second of decoded 5.1 audio contains 48,000 sample values for each of six channels. The decoder produces those channels together from one encoded audio track. Selecting commentary changes tracks; changing the receiver's speaker layout changes what happens to channels within the selected track.
Selection changes the work, even with the same picture
An Emby session playing Audio 1 may use a different audio output path from one playing Audio 2. The German stereo track may already suit the output, while a surround track might need downmixing or a codec conversion. The video sequence remains the same.
Subtitle selection is another independent choice. A timed text sequence can be rendered by the app; a selected subtitle that the route cannot render separately may need to be incorporated into the video. The complete session therefore depends on the chosen combination, not every track stored in the source.
A track description normally includes a codec, technical properties, language, and sometimes a title and selection flags. “English commentary” in a title is separate from the language code. Those fields help distinguish two soundtracks with the same language.
When comparing a remux with its original, match tracks by these descriptions. Inspection tools may renumber the output after a track is removed, so “track 2” can refer to different content in the two files.