PIDs are the IDs associated with streams.  Streams are what make up channels - ie. video stream + audio stream + subtitles stream etc. Each table or elementary stream in a transport stream is identified by a 13-bit packet ID (PID). A demultiplexer extracts elementary streams from the transport stream in part by looking for packets identified by the same PID. In most applications, time-division multiplexing will be used to decide how often a particular PID appears in the transport stream.

PID Filtering

Digital tuners lock on to bunches of channels (transponders, multiplexes). By default, tuners pass the full set of channels directly to software (i.e. TsWriter) and the software chooses which channels to show to the user.

Computer "buses" (eg. USB, Firewire, PCI, PCIe) have bandwidth limits. Sometimes the bus that a tuner is connected to cannot cope with carrying the full set of channels that the tuner would usually pass to software (for example, attempting to pass a 30 Mbps transponder stream over a 12 Mbps USB 1 connection won't work).  If you ignore bus limits and try to pass more data than a bus can handle then very bad/strange things will happen (stream corruption, stuttering, unpredictable stuff...).

PID filtering is instructing a tuner not to pass the full set of available streams, thereby avoiding the problems that might otherwise happen.

Such situations aren't that common these days, but they occur occasionally with USB 1 tuners (or tuners connected to USB 1 ports) and Firewire ports. PID filtering may also be preferrable in combination with networked tuners like the HDHomeRun in order to to reduce network congestion.

At present the only specific case where MediaPortal uses PID filtering is with Digital Everywhere tuners (Firewire); we only enable it when they are tuned to DVB-S2 transponders with high data rates.

Related Terms

• PAT
• Transport Stream (.ts)