Patent ID: 7010034

Claim:
A method of compressing a video signal, the method comprising: predictively encoding ( 10 , 11 ) frames (X) of said video signal with reference to a prediction frame(X p ), calculating ( 20 ) a quantization parameter (q) for each encoded frame, quantizing ( 12 ) the encoded frames in accordance with said quantization parameter, characterized in that said step of calculating the quantization parameter includes calculating a first quantization parameter (q) representing a first quality or bit rate for quantizing selected first frames (P) of said predictively encoded frames, and a second quantization parameter (F.q) representing a second quality or bit rate that is lower than said first quality or bit rate for quantizing selected second frames (P′) of the video signal, said second quantization parameter degrading the second quality compared to the first quality, wherein said predictively encoded frames constitute a series of successive frames, the second selected frames being every other frame of said series, the method further including: decompressing ( 15 – 18 ) the compressed second frames to constitute the prediction frame (X p ) for predictively encoding the first frames.