MPEG Program Stream
MPEG program stream multiplexes related encoded streams into variable-size packs for storage and playback in comparatively reliable environments.
An older MPG movie and the video objects on a DVD can organize media through MPEG program stream (PS). This systems layer arranges encoded components for synchronized playback; it does not define their picture compression.
PS uses packs, which contain a pack header and packetized elementary-stream data. Unlike the fixed small packets of transport stream, pack and PES organization is suited to a comparatively reliable source such as stored media.
Pack clocks, PES timestamps, and stream identifiers
The reader identifies the pack structure and its systems clock information. It then examines PES packet headers to identify components and obtain timestamps where supplied. Payload belonging to video is routed to video decoding, while audio payload is routed to an audio decoder.
| Information | Role in this process |
|---|---|
| Pack header and system timing | Describe the multiplex's delivery timing |
| Stream identifiers | Distinguish components or private-data arrangements |
| PES PTS/DTS, when present | Schedule presentation and decoding |
| Encoded payload | Supplies the codec's media data |
Stream identifiers do not all imply one universal codec choice. DVD, for example, defines additional conventions for private-stream audio and subpictures. The systems reader must understand the relevant arrangement before the appropriate codec receives its bytes.
Reading order and viewing order
Interleaving puts pieces of different components within the package. Their timestamps associate them with a shared schedule. The file reader does not need to play the entire video portion before the entire audio portion; it supplies queues for both so the player can present them together.
A component's timestamps and codec setup can therefore be essential when copying its elementary data into another package. Preserving only payload while losing timing is not the same as preserving the presentation.
What a DVD adds around VOB media
DVD-Video uses constrained program-stream-based video objects, commonly stored in VOB files. A title can span several such files and use navigation that chooses cells or angles. Its IFO descriptions supply title and programme-chain organization outside the ordinary act of decoding a VOB's packets.
Opening one VOB demonstrates that its media can be read. It does not resolve the disc's intended complete title. Joining filenames in order similarly follows storage naming rather than the navigation that selected the presentation.
When preparing a disc-derived source for an Emby library, the useful boundary is the intended title and its selected components. A remux can retain their encoding while writing a new timed package, after the source's presentation choices have been resolved.