Method of inserting additonal data into a compressed signal

• US 20040114687A1
• Filed: 01/08/2004
• Published: 06/17/2004
• Est. Priority Date: 02/09/2001
• Status: Active Grant

• Current Assignee: Broadcast UK Limited
• Original Assignee: Radioscape Limited
• Inventors: Ferris, Gavin Robert, Woodward, Michael Vincent
• Granted Patent: US 7,346,517 B2
• Time in Patent Office: Days
• US Class Current: 375/240.11
• CPC Class Codes: G10L 19/00 Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis in musical instruments G10H

Abstract

Many compressed audio or video frames contain silence (if audio), or a blank image (if video); these essentially information content free (e.g. silent if audio or blank if video) frames can be both detected whilst still in compressed form and then used to carry the additional data. In an MPEG implementation, subbands associated with silent frames are rendered digitally silent and then used to carry PAD (Programme Associated Data).

Claims

1. A method of inserting additional data into a compressed signal comprises the steps of:

(a) detecting whether the information content of a media data portion of a frame in the compressed signal falls, in whole or part, below a threshold;

(b) discarding the whole or part of any such media data portion which falls below the information content threshold;

(c) inserting the additional data into an ancillary portion of the frame to occupy space vacated by the discarded portion.

2. The method of claim 1 in which the compressed signal is a frequency domain representation with sub-bands and, for the whole or part of any media data portion of a frame for which the original information content falls below a threshold, some or all of the data in the subbands is discarded.

3. The method of claim 2 in which some of the data in the subband is deliberately left in the media data portion of a frame or applicable part of a frame, despite falling below the information content threshold.

4. The method of claim 2 in which noise is deliberately introduced into the media data portion of a frame or applicable part of a frame which has been discarded.

5. The method of claim 2 in which the step of detecting whether the original information content of a media data portion of a frame falls, in whole or part, below a threshold involves the following steps:

(a) examining amplitude data coded in the compressed signal;

(b) determining the presence or absence of information content in the compressed signal in dependence on the results of the amplitude examination.

6. The method of claim 5 in which the examination of the amplitude data coded in the compressed signal involves a comparison to a threshold value.

7. The method of claim 5 in which the amplitude data is coded as scale factors.

8. The method of claim 5 in which an average scale factor for a given media data portion of a frame, being a mean, median or mode, is used in the amplitude examination.

9. The method of claim 5 in which scale factor indices are used in the amplitude examination.

10. The method of claim 5 in which scale factor values are used in the amplitude examination.

11. The method of claim 1 where a psycho-acoustic or masking model is used to determine the threshold levels.

12. The method of claim 11 in which the psycho-acoustic or masking model indicates whether any subbands are non-optimally quantised and can therefore be compressed further to enable the ancillary data portion to be increased in size to carry the additional data.

13. The method of claim 1 in which the additional data is PAD.

14. The method of claim 1 where the additional data is MPEG ID3 tags.

15. The method of claim 1 in which the signal is an MPEG signal encoding using CBR.

16. The method of claim 1 in which the signal is an MPEG signal encoding using VBR.

17. Computer software adapted to perform the method of any preceding claim 1-16.

18. Computer hardware adapted to perform the method of any preceding claim 1-16.

19. Chip level devices adapted to perform the method of any preceding claim 1-16.