Low-complexity spatial downscaling video transcoder and method thereof

• US 20050169377A1
• Filed: 07/08/2004
• Published: 08/04/2005
• Est. Priority Date: 02/04/2004
• Status: Active Grant

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Lee, Yuh-Ruey, Chou, Yeh-Kai, Lin, Chia-Wen
• Granted Patent: US 7,180,944 B2
• Time in Patent Office: Days
• US Class Current: 375/240.160
• CPC Class Codes: H04N 19/159 Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/40 using video transcoding, i.e. partial or full decoding of a coded input stream followed by re-encoding of the decoded output stream
• CPC Class Codes: H04N 19/48 using compressed domain processing techniques other than decoding, e.g. modification of transform coefficients, variable length coding [VLC] data or run-length data motion estimation in a transform domain H04N19/547; processing of decoded motion vectors H04N19/513
• CPC Class Codes: H04N 19/59 involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

A low-complexity spatial downscaling video transcoder and method thereof are disclosed. The transcoder comprises a decoder having a reduced DCT-MC unit, a DCT-domain downscaling unit, and an encoder. The decoder performs the DCT-MC operation at a reduced-resolution for P-/B-frames in an MPEG coded bit-stream. The DCT-domain downscaling unit is used for spatial downscaling in the DCT-domain. After the downscaling and the motion vectors re-sampling, the encoder determines the encoding modes and outputs the encoded bit-stream. Compared with the original CDDT, this invention can achieve significant computation reduction and speeds up the transcoder without any quality degradation.

Claims

1. A low-complexity spatial downscaling video transcoder, comprising:

a decoder having a reduced discrete cosine transform motion compensation (DCT-MC) unit, said decoder receiving incoming bit-streams, using said reduced DCT-MC unit to integrate the DCT-domain motion compensation and downscaling operations in the downscaling CDDT into a reduced-resolution DCT-MC for B or P frames in MPEG standard, performing the reduced-resolution decoding, generating an estimated motion vector, and performing a full-resolution decoding for I-frames in MPEG standard;

a DCT-domain downscaling unit outputting the downscaling results of the decoded I-frames for encoding; and

an encoder receiving said estimated vector and the downscaling results from said DCT-domain downscaling unit, determining encoding modes and outputting encoded bit-streams.

2. The low-complexity spatial downscaling video transcoder as claimed in claim 1, wherein said low-complexity operation performs the full-resolution decoding for all I and P frames and the reduced-resolution decoding for all B frames.

3. The low-complexity spatial downscaling video transcoder as claimed in claim 1, wherein said low-complexity operation is to perform the reduced-resolution decoding for all P and B frames.

4. The low-complexity spatial downscaling video transcoder as claimed in claim 2, wherein said operation means extracting only the low-frequency coefficients on performing the DCT-MC downscaling operation in said decoder for B-frames.

5. The low-complexity spatial downscaling video transcoder as claimed in claim 3, wherein said low-complexity operation is to extract only the low-frequency coefficients on performing the DCT-MC downscaling operation in said decoder for all P-frames and B-frames.

6. The low-complexity spatial downscaling video transcoder as claimed in claim 1, wherein said reduced-resolution decoding is performed by decoding with a quarter resolution.

7. The low-complexity spatial downscaling video transcoder as claimed in claim 2, said reduced DCT-MC unit further comprising:

a full frame memory, saving said decoded and inverse quantized incoming bit-streams or reconstructed frames of downscaled resolution;

a full DCT-MC_dec, performing the discrete cosine transform and motion compensation of full resolution for P-frames; and

a spatial downscaled DCT-MC_dec, performing the discrete cosine transform and motion compensation of reduced resolution for B-frames.

8. The low-complexity spatial downscaling video transcoder as claimed in claim 3, said reduced DCT-MC unit further comprising:

a downscaled frame memory, saving said decoded and inverse quantized incoming bit-streams or reconstructed frames of downscaled resolution;

a low-frequency coefficient extractor, extracting the low-frequency coefficients of incoming data from said downscaled frame memory; and

a spatial downscaled DCr-MC_dec, performing the downscaling and motion compensation of reduced resolution for B-frames and P-frames.

9. A low-complexity spatial downscaling video transcoding method, comprises the following steps:

(a) receiving incoming bit-streams, using a reduced discrete cosine transform motion compensation (DCT-MC) unit to integrate the DCT-domain motion compensation and downscaling operations into a reduced-resolution DCT-MC for B or P frames in MPEG standard, performing the reduced-resolution decoding, generating an estimated motion vector, and performing the full-resolution decoding for I-frames in MPEG standard;

(b) outputting the downscaling results of the decoded I-frames for encoding; and

(c) receiving said estimated vector and the downscaling results from said DCT-domain downscaling unit, determining encoding modes and outputting encoded bit-streams.

10. The low-complexity spatial downscaling video transcoding method as claimed in claim 9, wherein said B frames are decoded by extracting only the low-frequency coefficients on performing the DCT-MC downscaling operation in said step (a), while said I and P frames are decoded at a full picture resolution.

11. The low-complexity spatial downscaling video transcoding method as claimed in claim 9, wherein said B and P frames are decoded by extracting only the low-frequency coefficients on performing the DCT-MC downscaling operation in said step (a), while said I frames are decoded at a full picture resolution.

12. The low-complexity spatial downscaling video transcoding method as claimed in claim 9, wherein a re-sampling process is further included for motion vectors after said reduced DCT-MC operation.

13. The low-complexity spatial downscaling video transcoding method as claimed in claim 12, wherein said re-sampling process is as follows:

for a reduced N_x×

N_y system, original N_x×

N_y macroblocks (MBs) are reduced to one macroblock, and the re-sampled motion vector is the activity-weighted median of the N_x×

N_y incoming vector set V={v₁, v₂, . . . , v<sub>Nx×

Ny</sub>}.

14. The low-complexity spatial downscaling video transcoding method as claimed in claim 9, wherein for a reduced N_x×

N_y system, original N_x×

N_y macroblocks are reduced to one macroblock, then the rules for determining the coding modes in said step (c) are as follows;

(c1) If all original macroblocks being intra-coded, then the mode for said downscaled macroblock is set as intra-coded;

(c2) If all original macroblocks being skipped, said resulting downscaled macroblock is also skipped; and

(c3) the mode for said downscaled macroblock is set as inter-coded in all other cases.

15. The low-complexity spatial downscaling video transcoding method as claimed in claim 13, wherein the squared sum of DCT coefficients of said MB is adopted as the measurement of said motion vector.

16. The low-complexity spatial downscaling video transcoding method as claimed in claim 10, wherein said B frames are decoded with a quarter resolution.

17. The low-complexity spatial downscaling video transcoding method as claimed in claim 11, wherein said all P and B frames are decoded with a quarter resolution.