Robust method for achieving audio/video synchronization in MPEG decoders in personal video recording applications

A receiver for receiving an MPEG encrypted transport stream and outputting audio and video signals, comprising:

• a decryptor adapted to receive the encrypted transport stream, decrypt the encrypted transport stream and output a decrypted transport stream;
• a selector adapted to receive the decrypted transport stream, adapted to select packets associated with one or more programs and adapted to create a partial transport containing only packets associated with the one or more programs, adapted to add a time stamp based on a receiver record clock to each packet in the partial transport stream and adapted to output the partial transport stream;
• a storage sub-system adapted to receive and store the partial transport stream;
• a de-multiplexer adapted to receive the partial transport stream, adapted to convert the partial transport stream to an audio elementary stream and a video elementary stream, adapted to change the values in presentation time stamp and decoding time stamp fields of each header of each packet of the audio elementary stream and of the video elementary stream to compensate for the amount of time the partial transport stream is stored in the storage sub-system;
• an audio decoder adapted to receive and to decode the audio elementary stream and output an audio signal;
• and
• a video decoder adapted to receive and to decode the video elementary stream and output a video signal.

A method of synchronization of audio and video in an MPEG decoder comprising:

• decrypting a transport stream;
• de-multiplexing the transport stream;
• extracting the value of a first program clock reference field from the header of a first packet associated with a program in the transport stream;
• de-multiplexing the transport stream into an audio elementary stream and a video elementary stream;
• adding a difference between a current time and a value of a first program clock reference field in the header of a packet in the decrypted transport stream, the packet associated with a program to be stored to each presentation time stamp field and each decoding time stamp field of each header of each packet in the audio and video elementary streams associated with the program to be stored;
• storing the audio and video elementary streams;
• upon reading out the audio and video elementary streams, adding a difference between a time when the audio and video elementary streams were stored and a play time when the audio and video elementary streams are read out of storage to each presentation time stamp field and each decoding time stamp field of each header of each packet in the audio and video elementary streams;
• and
• decoding the audio and video elementary streams.

A method of synchronization of audio and video in an MPEG decoder comprising:

• decrypting a transport stream;
• selecting packets associated with one or more programs and creating a partial transport stream containing only packets associated with the one or more programs;
• adding a time stamp based on a current record time to each header of each packet in the partial transport stream;
• storing the partial transport stream;
• reading out partial transport stream;
• de-multiplexing the partial transport stream into an audio elementary stream and a video elementary stream;
• adding a difference between a value of a first program clock reference field in the header of a packet in the decrypted transport stream, the packet associated with a program to be stored, and a current time to each presentation time stamp field and each decoding time stamp field of each header of each packet in the audio and video elementary streams;
• and
• decoding the audio and video elementary streams.