Processing video data

1. Video data processing apparatus configured to process video data for downloading to mobile devices, in which the total data volume of an output file is limited, comprising:

a coder for coding an input video clip of image frames to produce a first coded video data file having a predetermined data volume;

and a processing device arranged to receive from said coder a measure of spatial data loss caused by said coding, to compare said obtained measure of data loss against a predetermined data loss value and if too much spatial loss has occurred, to remove frames from said input clip and to recode the input video clip to produce an output data file;

wherein said re-coding step with even fewer frames is performed again until the degree of spatial loss has become acceptable;

wherein the frame-rate is not allowed to drop below a predetermined minimum;

and if too much spatial loss still occurs, audio quality is reduced.

2. The apparatus as claimed in claim 1 , wherein said mobile devices are mobile cellular telephones.

3. The apparatus as claimed in claim 1 , wherein standard files are written to a standard file storage device and files formatted from standard files are written to a formatted files storage device.

4. A method of optimising a video data file for downloading to a mobile device, in which the total data volume of the file is limited, comprising the steps of:

coding an input video clip of image frames to produce a first coded video data file having a predetermined data volume;

obtaining a measure of spatial data loss caused by said coding;

comparing said obtained measure of data loss against a predetermined data loss value;

and if too much spatial loss has occurred, removing frames from said input clip and re-coding the input video clip to produce an output data file;

wherein said re-coding step with even fewer frames is performed again until the degree of spatial loss has become acceptable;

wherein the frame-rate is not allowed to drop below a predetermined minimum;

and if too much spatial loss still occurs, audio quality is reduced.

5. The method as claimed in claim 4 , wherein the measure of spatial data loss is obtained by receiving an indication of quantization or truncation.

6. The method as claimed in claim 4 , wherein said measure of spatial data loss is averaged over the clip.

7. The method as claimed in claim 4 , wherein the optimised data is downloaded from a server to a personal computer and then said data is transferred from said personal computer to the mobile device, wherein

the data transferred from the server to the computer is encrypted and said encrypted file is transferred to the mobile device: and

a decryption key is transmitted directly from the server to the mobile device.

8. The method as claimed in claim 7 , wherein the decryption key is transmitted to the mobile device using a data messaging system, such as a short message service.

9. A non-transitory computer-readable medium encoded with a computer program that, when executed by a computer, causes the computer to perform a method of processing video data for downloading to mobile devices, in which the total data volume of an output file is limited, comprising the steps of:

coding an input video clip of image frames to produce a first coded video data file having a predetermined data volume;

obtaining a measure of spatial data loss caused by said coding;

comparing said obtained measure of data loss against a predetermined data loss value;

and if too much spatial loss has occurred, removing frames from said input clip and recoding the input video clip to produce an output data file;

wherein said computer program causes said computer to perform said re-coding step again with even fewer frames is performed again until the degree of spatial loss has become acceptable;

wherein the frame-rate is not allowed to drop below a predetermined minimum;

and if too much spatial loss still occurs, audio quality is reduced.

10. The computer-readable medium as claimed in claim 9 , wherein the measure of spatial data loss is obtained by receiving an indication of quantization or truncation.

11. The computer-readable medium as claimed in claim 9 , wherein said measure of spatial data loss is averaged over the clip.