Transcoder and transcoding method operating in a transform domain for video coding schemes possessing different transform kernels

1. A transcoder for converting a digital video signal from a first format into a second format in a transform domain, the first format and the second format being respectively adopted by video coding schemes possessing different DCT transform kernels, the transcoder comprising:

a transform-domain decoder, coupled to the digital video signal, for decoding the digital video signal of the first format to generate a first DCT-domain signal, the first DCT-domain signal corresponding to a first DCT transform of the first format in the transform domain;

a transform kernel converter, coupled to the transform-domain decoder, for converting the first DCT-domain signal into a second DCT-domain signal, the second DCT-domain signal corresponding to a second DCT transform of the second format in the transform domain; and

a transform-domain encoder, coupled to the transform kernel converter, for generating a resultant video signal encoded in the second format according to a differential signal, the transform-domain encoder comprising:

an adder for subtracting a prediction signal from the second DCT-domain signal to generate the differential signal; and

an intra-predictor, coupled to the adder and the transform kernel converter, for generating the prediction signal in the transform domain according to the second DCT-domain signal.

2. The transcoder of claim 1 , wherein the transform-domain encoder further comprises a compressing module, coupled to the adder, for compressing the differential signal to generate the resultant video signal.

3. The transcoder of claim 1 , wherein the transform kernel converter generates the second DCT-domain signal by performing a linear transform on the first DCT-domain signal, and the linear transform corresponds to a combination of the second DCT transform and an inverse transform of the first DCT transform.

4. The transcoder of claim 1 , wherein the transform kernel converter further performs down sampling when converting the first DCT-domain signal into the second DCT-domain signal.

5. The transcoder of claim 1 , wherein the intra-predictor selects a best prediction from a plurality of candidate predictions in the transform domain to determine the prediction signal, and the candidate predictions correspond to a plurality of prediction modes, respectively.

6. The transcoder of claim 5 , wherein the video coding schemes are block-based video coding schemes, the candidate predictions corresponding to a specific block of a specific image frame are generated according to at least a block adjacent to the specific block on the specific image frame and a plurality of predetermined operation matrices, and each of the prediction modes chooses a specific subset of the predetermined operation matrices to generate a corresponding candidate prediction.

7. The transcoder of claim 1 , wherein the second format corresponds to an H.264 specification.

8. The transcoder of claim 7 , wherein the first format corresponds to an MPEG-2 specification.

9. A transcoding method for converting a digital video signal from a first format into a second format in the transform domain, the first format and the second format being respectively adopted by video coding schemes possessing different DCT transform kernels, the transcoding method comprising:

decoding the digital video signal of the first format to generate a first DCT-domain signal, the first DCT-domain signal corresponding to a first DCT transform of the first format in transform domain;

converting the first DCT-domain signal into a second DCT-domain signal, the second DCT-domain signal corresponding to a second DCT transform of the second format in transform domain; and

generating a resultant video signal encoded in the second format according to a differential signal, comprising:

subtracting a prediction signal from the second DCT-domain signal to generate the differential signal; and

generating the prediction signal in the transform domain according to the second DCT-domain signal.

10. The transcoding method of claim 9 , wherein the step of generating the resultant video signal further comprises compressing the differential signal to generate the resultant video signal.

11. The transcoding method of claim 9 , wherein the transform kernel converter generates the second DCT-domain signal by performing a linear transform on the first DCT-domain signal, and the linear transform corresponds to a combination of the second DCT transform and an inverse transform of the first DCT transform.

12. The transcoding method of claim 9 , wherein the step of converting the first DCT-domain signal into the second DCT-domain signal further performs down-sampling when converting the first DCT-domain signal into the second DCT-domain signal.

13. The transcoding method of claim 9 , wherein the step of generating the prediction signal selects a best prediction from a plurality of candidate predictions in the transform domain to determine the prediction signal, and the candidate predictions correspond to a plurality of prediction modes, respectively.

14. The transcoding method of claim 13 , wherein the video coding schemes are block-based video coding schemes, the candidate predictions corresponding to a specific block of a specific image frame are generated according to at least a block adjacent to the specific block on the specific image frame and a plurality of predetermined operation matrices, and each of the prediction modes chooses a specific subset of the predetermined operation matrices to generate a corresponding candidate prediction.

15. The transcoding method of claim 9 , wherein the second format corresponds to an H.264 specification.

16. The transcoding method of claim 9 , wherein the first format corresponds to an MPEG-2 specification.

17. A transcoder for converting a digital video signal from a first format into a second format in the transform domain, the first format and the second format being respectively adopted by video coding schemes possessing different DCT transform kernels, the transcoder comprising:

means for decoding the digital video signal of the first format to generate a first DCT-domain signal, the first DCT-domain signal corresponding to a first DCT transform of the first format in the transform domain;

means for converting the first DCT-domain signal into a second DCT-domain signal, the second DCT-domain signal corresponding to a second DCT transform of the second format in the transform domain; and

means for generating a resultant video signal encoded in the second format according to a differential signal, comprising:

subtracting a prediction signal from the second DCT-domain signal to generate the differential signal; and

generating the prediction the transform domain according to the second DCT-domain signal.

18. A transcoder for converting a digital video signal from a first format into a second format in the transform domain, the first format and the second format being respectively adopted by video coding schemes possessing different DCT transform kernels, the transcoder comprising:

a processor; and

a storage device, coupled to the processor, for storing a transcoding program, wherein the transcoding program executed by the processor is capable of:

decoding the digital video signal of the first format to generate a first DCT-domain signal, the first DCT-domain signal corresponding to a first DCT transform of the first format in the transform domain;

converting the first DCT-domain signal into a second DCT-domain signal, the second DCT-domain signal corresponding to a second DCT transform of the second format in the transform domain; and

generating a resultant video signal encoded in the second format according to a differential signal, comprising:

subtracting a prediction signal from the second DCT-domain signal to generate the differential signal; and

generating the prediction signal in the transform domain according to the second DCT-domain signal.