What is periodically inserted in an MPEG-2 TS to assist the decoder in identifying packet identifiers (PID)?

The Program Specific Information (PSI) is crucial in the MPEG-2 Transport Stream (TS) as it provides essential metadata that helps the decoder understand the structure and contents of the video and audio streams. The PSI includes several vital tables, such as the Program Association Table (PAT) and the Program Map Table (PMT), which contain information about the packet identifiers (PIDs) for different programs and their associated components (like audio, video, subtitles, etc.).

By using the information in PSI, the decoder can accurately locate and decode the specific streams of interest from the multiplexed transport stream. This process is essential for managing multiple programs within a single transport stream, ensuring that viewers receive the correct audiovisual content without confusion.