Video compression

An arrangement for compressing a video signal, the arrangement comprising:

• encoding means (10,11) for predictively encoding frames (X) of said video signal with reference to a prediction frame (Xp),
• calculation means (20) for calculating a quantization parameter (q) for each encoded frame,
• a quantizer (12) for quantizing the encoded frames in accordance with said quantization parameter,
• characterized in that said calculation means (20) are arranged to calculate a first quantization parameter 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 arrangement further including:
• means (15–18) for decompressing the compressed second frames to constitute said prediction frame (Xp) for predictively encoding first selected frames.

A method of transmitting or recording a video signal, the method comprising:

• generating the compressed video signal comprising:
• a prediction frame (Xp),
• predictively encoded (10,11) frames (X) that have been predictively encoded with reference to the prediction frame (Xp),
• respective quantization parameters (q) for respective encoded frames, the encoded frames having been quantized (12) in accordance with said respective quantization parameters, the quantization parameters including first quantization parameters (q) representing a first quality or bit rate for quantizing selected first frames (P) of said predictively encoded frames, and second quantization parameters (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 parameters 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;
• and
• transmitting or storing the compressed video signal.

An arrangement for transmitting or recording a video signal, the arrangement comprising:

• means (100) for generating the compressed video signal comprising:
• a prediction frame (Xp);
• predictively encoded (10,11) frames (X) that have been predictively encoded with reference to the prediction frame (Xp), and
• respective quantization parameters (q) for respective encoded frames, the encoded frames having been quantized (12) in accordance with said respective quantization parameters, the quantization parameters including first quantization parameters (q) representing a first quality or bit rate for quantizing selected first frames (P) of said predictively encoded frames, and second quantization parameters (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 parameters 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;
• and
• means (108, 120) for transmitting or recording the compressed video signal.