Method and apparatus for modifying a data rate of a video signal

• US 7,801,213 B2
• Filed: 07/25/2007
• Issued: 09/21/2010
• Est. Priority Date: 09/18/2006
• Status: Active Grant

• Current Assignee: Imagine Communications Limited (Gores Broadcast Holdings LLC)
• Original Assignee: RGB Networks, Inc. (Gores Broadcast Holdings LLC)
• Inventors: Monta, Peter, Krause, Edward A.
• Primary Examiner(s): Dastouri; Mehrdad
• Assistant Examiner(s): Huber; Jeremaiah C
• Application Number:
  US11/881,209
• Publication Number:
  US 20080072267A1
• Time in Patent Office: 1,154 Days
• Field of Search: 375/240.01
• US Class Current: 375/240.01
• CPC Class Codes: H04N 19/12 Selection from among a plurality of transforms or standards, e.g. selection between discrete cosine transform [DCT] and sub-band transform or selection between H.263 and H.264
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/159 Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction
• 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 21/4344 Remultiplexing of multiplex streams, e.g. by modifying time stamps or remapping the packet identifiers
• CPC Class Codes: H04N 21/440254 by altering signal-to-noise parameters, e.g. requantization

Abstract

Methods, apparatus, and systems for modifying the data rate of a video signal are provided. A compressed video signal is received. A closed-loop transrating path for modifying a data rate of the video signal and an open-loop transrating path for modifying the data rate of the video signal are provided. One of the open-loop transrating path or the closed-loop transrating path is selected for modifying the data rate of at least a portion of the video signal. Pixel quantization error control may be provided in the closed loop transrating path.

Claims

1. A method for modifying a data rate of a video signal, comprising:

receiving a compressed video signal;

providing a closed-loop transrating path for modifying a data rate of the video signal;

providing an open-loop transrating path for modifying the data rate of the video signal;

automated selecting of one of said open-loop transrating path or said closed-loop transrating path for modifying the data rate of at least a portion of said video signal;

said closed-loop transrating path and said open loop transrating path are operable simultaneously and are adapted to accept at least different portions of said video signal; and

providing pixel quantization error control in said closed loop transrating path, said pixel quantization error control comprising;

obtaining errors from quantization of transformation coefficients of incoming pixels of the video signal;

deriving pixel errors from said quantization errors;

storing said pixel errors;

retrieving said stored pixel errors during modification of said data rate of associated pixels;

deriving error correction quantization data from said retrieved pixel errors; and

applying said error correction quantization data in order to prevent accumulation of requantization artifacts during said modification of said data rate of said associated pixels;

wherein;

said closed-loop transrating path is selected for modifying the data rate of I-frames and P-frames of said video signal;

said open-loop transrating path is selected for modifying the data rate of B-frames of said video signal;

in the event that at least one of;

(a) the open-loop transrating path is idle; and

(b) the closed-loop path is oversubscribed, the open-loop transrating path is selected for modifying the data rate of I-frames and P-frames of the video signal without said pixel quantization error control; and

in the event that at least one of;

(a) the closed-loop transrating path is idle; and

(b) the open-loop path is oversubscribed, selecting the closed-loop transrating path for modifying the data rate of B-frames.

2. A method in accordance with claim 1, wherein said closed-loop transrating path and said open loop transrating path are operable simultaneously and are adapted to accept frames from multiple video signals.

3. A method in accordance with claim 1, further comprising:

an additional open-loop transrating path for modifying the data rate of the video signal.

4. A method in accordance with claim 3, wherein said two open-loop transrating paths and said closed-loop transrating path are operable simultaneously.

5. A method in accordance with claim 1, wherein said open-loop transrating path comprises:

variable length decoding of said video signal to provide quantized transform coefficients;

performing an inverse quantization operation on said transform coefficients to scale said transform coefficients;

performing a quantization operation on said scaled transform coefficients to re-scale said transform coefficients to achieve a desired data rate; and

variable length encoding of said re-scaled transform coefficients to provide a video signal at said desired data rate.

6. A method in accordance with claim 1, wherein said closed-loop transrating path comprises:

variable length decoding of said video signal to provide quantized transform coefficients;

performing an inverse quantization operation on said transform coefficients to scale said transform coefficients;

performing a quantization operation on said scaled transform coefficients to re-scale said transform coefficients to achieve a desired data rate;

variable length encoding of said re-scaled transform coefficients to provide a video signal at said desired data rate;

obtaining errors from the quantization operation in the form of error transform coefficients;

performing an inverse transformation process on said error transform coefficients to provide pixel errors in the pixel domain;

storing said pixel errors;

retrieving said stored pixel errors when performing a motion compensation operation on associated pixels;

performing a transformation process on said motion compensated pixel errors to provide error correction transform coefficients; and

adding said error correction transform coefficients to said scaled transform coefficients obtained from said inverse quantization of said associated pixels in order to prevent accumulation of requantization artifacts during said quantization operation on said scaled transform coefficients.

7. A method in accordance with claim 1, further comprising:

providing a plurality of open-loop and closed loop transrating paths for modifying the data rate of the video signal.

8. A method in accordance with claim 7, wherein said plurality of open-loop and closed-loop transrating paths are operable simultaneously.

9. Apparatus for modifying a data rate of a video signal, comprising:

means for receiving a compressed video signal;

a closed-loop transrating path for modifying a data rate of the video signal;

an open-loop transrating path for modifying the data rate of the video signal;

means for selecting one of said open-loop transrating path or said closed loop transrating path for modifying the data rate of at least a portion of said video signal;

said closed-loop transrating path and said open loop transrating path are operable simultaneously and are adapted to accept at least different portions of said video signal; and

means for providing pixel quantization error control in said closed loop transrating path, said means for providing said pixel quantization error control comprising;

means for obtaining errors from quantization of transformation coefficients of incoming pixels of the video signal;

means for deriving pixel errors from said quantization errors;

storage means for storing said pixel errors;

means for retrieving said stored pixel errors during modification of said data rate of associated pixels;

means for deriving error correction quantization data from said retrieved pixel errors; and

means for applying said error correction quantization data in order to prevent accumulation of requantization artifacts during said modification of said data rate of said associated pixels;

wherein;

said closed-loop transrating path is selected for modifying the data rate of I-frames and P-frames of said video signal;

said open-loop transrating path is selected for modifying the data rate of B-frames of said video signal;

in the event that at least one of;

(a) the open-loop transrating path is idle; and

(b) the closed-loop path is oversubscribed, the open-loop transrating path is selected for modifying the data rate of I-frames and P-frames of the video signal without said pixel quantization error control; and

in the event that at least one of;

(a) the closed-loop transrating path is idle; and

(b) the open-loop path is oversubscribed, selecting the closed-loop transrating path for modifying the data rate of B-frames.

10. Apparatus in accordance with claim 9, wherein said closed-loop transrating path and said open loop transrating path are operable simultaneously and are adapted to accept frames from multiple video signals.

11. Apparatus in accordance with claim 9, further comprising:

an additional open-loop transrating path for modifying the data rate of the video signal.

12. Apparatus in accordance with claim 11, wherein said two open-loop transrating paths and said closed-loop transrating path are operable simultaneously.

13. Apparatus in accordance with claim 9, wherein said open-loop transrating path comprises:

a variable length decoder for variable length decoding of said video signal to provide quantized transform coefficients;

an inverse quantization module for performing an inverse quantization operation on said transform coefficients to scale said transform coefficients;

a quantizer module for performing a quantization operation on said scaled transform coefficients to re-scale said transform coefficients to achieve a desired data rate; and

a variable length encoder for variable length encoding of said re-scaled transform coefficients to provide a video signal at said desired data rate.

14. Apparatus in accordance with claim 9, wherein said closed-loop transrating path comprises:

a variable length decoder for variable length decoding of said video signal to provide quantized transform coefficients;

an inverse quantization module for performing an inverse quantization operation on said transform coefficients to scale said transform coefficients;

a quantization module for performing a quantization operation on said scaled transform coefficients to re-scale said transform coefficients to achieve a desired data rate;

a variable length encoder for variable length encoding of said re-scaled transform coefficients to provide a video signal at said desired data rate;

means for obtaining errors from the quantization operation in the form of error transform coefficients;

an inverse transform module for performing an inverse transformation process on said error transform coefficients to provide pixel errors in the pixel domain;

storage means for storing said pixel errors;

means for retrieving said stored pixel errors when performing a motion compensation operation on associated pixels;

a transform module for performing a transformation process on said motion compensated pixel errors to provide error correction transform coefficients; and

adder means for adding said error correction transform coefficients to said scaled transform coefficients obtained from said inverse quantization of said associated pixels in order to prevent accumulation of requantization artifacts during said quantization operation on said scaled transform coefficients.

15. Apparatus in accordance with claim 9, further comprising:

a plurality of open-loop and closed loop transrating paths for modifying the data rate of the video signal.

16. Apparatus in accordance with claim 15, wherein said plurality of open-loop and closed-loop transrating paths are operable simultaneously.