Rate control for bitstream re-encoding

• US 6,763,067 B2
• Filed: 10/09/2001
• Issued: 07/13/2004
• Est. Priority Date: 10/10/2000
• Status: Active Grant

• Current Assignee: MediaTek USA Incorporated (MediaTek, Inc.)
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Hurst, Robert N.
• Primary Examiner(s): Kelley, Chris
• Assistant Examiner(s): CZEKAJ, DAVID J
• Application Number:
  US09/973,643
• Publication Number:
  US 20020067768A1
• Time in Patent Office: 1,008 Days
• Field of Search: 375/240.01, 375/240.03, 375/240-2-2, 375/240-2-2, 375/240-3-2
• US Class Current: 375/240.03
• CPC Class Codes: H04N 19/126 Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
• CPC Class Codes: H04N 19/15 by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
• CPC Class Codes: H04N 19/152 by measuring the fullness of the transmission buffer
• 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 19/61 in combination with predictive coding
• CPC Class Codes: H04N 21/23406 involving management of server-side video buffer
• CPC Class Codes: H04N 21/44004 involving video buffer management, e.g. video decoder buffer or video display buffer

Abstract

Processing is applied to convert an input compressed video bitstream into an output compressed video bitstream having a different bit rate and/or representing different imagery from the input bitstream. The bitstream conversion processing is adjusted based on control parameters that are generated by comparing analogous measurements made to the input and output bitstreams so that subsequent measurements of the output bitstream will more closely match subsequent measurements of the input bitstream. In certain embodiments, the bitstream conversion processing involves decoding the input bitstream, optionally applying image processing functions to the resulting decoded video data, and re-encoding the resulting processed video data to generate the output bitstream. In one embodiment, the quantization data used during quantization of DCT coefficients during the re-encoding process are scaled using quantization re-scale factors (QRFs) generated by comparing the arrival margin for each frame in the input bitstream to the arrival margin for the corresponding frame in the output bitstream, where the arrival margin is defined as the amount of time between when the last bit of a frame has entered the decode buffer and when that frame is removed from the buffer.

Claims

1. A method for converting an input compressed video bitstream into an output compressed video bitstream, comprising the steps of:

(a) applying a process to convert the input bitstream into the output bitstream;

(b) generating one or more input measurements from the input bitstream;

(c) generating one or more output measurements from the output bitstream; and

(d) comparing the one or more input measurements to the one or more output measurements to generate one or more control parameters that are used to adjust the process so that subsequent output measurements will more closely match subsequent input measurements, wherein;

step (a) comprises the steps of;

(1) at least partially decoding the input bitstream to generate at least partially decoded video data; and

(2) re-encoding video data corresponding to the decoded video data to generate the output bitstream, wherein the one or more control parameters are used to adjust the re-encoding;

the one or more control parameters comprise quantization re-scale factor (QRF) values;

the re-encoding comprises quantization of DCT coefficients generated based on the input bitstraem;

quantizers used to quantize the DCT coefficients are generated based on quantization data recovered from the input bitstream and the QRF values; and

the QRF values are generated based on comparing arrival margins of corresponding frames in the input and output bitstreams.

2. The invention of claim 1, wherein step (a)(1) further comprises the step of applying image processing to the decoded video data to alter imagery represented in the decoded video data prior to the re-encoding of step (a)(2).

3. The invention of claim 1, wherein quantization matrices recovered from the input bitstream are adjusted based on the QRF values prior to the quantization.

4. The invention of claim 1, wherein quantization scale values recovered from the input bitstream are adjusted based on the QRF values prior to the quantization.

5. The invention of claim 1, wherein both quantization matrices and quantization scale values recovered from the input bitstream are adjusted based on the QRF values prior to the quantization.

6. The invention of claim 5, wherein both the quantization matrices and the quantization scale values recovered from the input bitstream are multiplied by the square root of the QRF values prior to the quantization.

7. The invention of claim 1, wherein the QRF values are scaled based on scale factors corresponding to picture coding type prior to the quantization.

8. The invention of claim 1, wherein steps (b)-(d) correspond to the implementation of a feedback loop filter that generates the one or more control parameters that are used to adjust the process of step (a).

9. The invention of claim 1, wherein:

the one or more input measurements includes arrival margin of frames in the input bitstream;

the one or more output measurements includes arrival margin of frames in the output bitstream; and

the arrival margins of corresponding frames in the input and output bitstreams are compared to generate the one or more control parameters that are used to adjust the process so that subsequent output arrival margins will more closely match subsequent input arrival margins.

10. The invention of claim 9, wherein step (a) comprises the steps of:

(1) at least partially decoding the input bitstream to generate at least partially decoded video data;

(2) applying image processing to the decoded video data to alter imagery represented in the decoded video data; and

(3) re-encoding video data corresponding to the decoded video data to generate the output bitstream, wherein the one or more control parameters are used to adjust the re-encoding.

11. The invention of claim 1, wherein:

the one or more input measurements includes actual bitcount of frames in the input bitstream;

the one or more output measurements includes actual bitcount of frames in the output bitstream; and

the actual bitcounts of corresponding frames in the input and output bitstreams are compared to generate the one or more control parameters that are used to adjust the process so that subsequent output arrival margins will more closely match subsequent input arrival margins.

12. The invention of claim 1, wherein:

the one more input measurements includes picture durations in the input bitstream;

the one or more output measurements includes picture durations in the output bitstream; and

the corresponding picture durations in the input and output bitstreams are compared to generate the one or more control parameters that are used to adjust the process so that subsequent output arrival margins will more closely match subsequent input arrival margins.

13. A machine-readable medium, having encoded thereon program code, wherein, when the program code is executed by a machine, the machine implements a method for converting an input compressed video bitstream into an output compressed video bitstream, comprising the steps of:

(a) applying a process to convert the input bitstream into the output bitstream;

(b) generating one or more input measurements from the input bitstream;

(c) generating one or more output measurements from the output bitstream; and

(d) comparing the one or more input measurements to the one or more output measurements to generate one or more control parameters that are used to adjust the process so that subsequent output measurements will more closely match subsequent input measurements, wherein;

step (a) comprises the steps of;

(1) at least partially decoding the input bitstream to generate at least partially decoded video data; and

(2) re-encoding video data corresponding to the decoded video data to generate the output bitstream, wherein the one or more control parameters are used to adjust the re-encoding;

the one or more control parameters comprise quantization re-scale factor (QRF) values;

the re-encoding comprises quantization of DCT coefficients generated based on the input bitstream;

quantizers used to quantize the DCT coefficients are generated based on quantization data recovered from the input bitstream and the QRF values; and

the QRF values are generated based on comparing arrival margins of corresponding frames in the input and output bitstreams.

14. A method for converting an input compressed video bitstream into an output compressed video bitstream, comprising the steps of:

(a) applying a process to convert the input bitstream into the output bitstream;

(b) generating one or more input measurements from the input bitstream;

(c) generating one or more output measurements from the output bitstream; and

(d) comparing the one or more input measurements to the one or more output measurements to generate one or more control parameters that are used to adjust the process so that subsequent output measurements will more closely match subsequent input measurements, wherein step (a) comprises the steps of;

(1) at least partially decoding the input bitstream to generate at least partially decoded video data; and

(2) re-encoding video data corresponding to the decoded video data to generate the output bitstream, wherein the one or more control parameters are used to adjust the re-encoding;

the one or more control parameters comprise quantization re-scale factor (QRF) values;

the re-encoding comprises quantization of DCT coefficients generated based on the input bitstream;

quantizers used to quantize the DCT coefficients are generated based on quantization data recovered from the input bitstream and the QRF values; and

both quantization matrices and quantization scale values recovered from the input bitstream are multiplied by the square root of the QRF values prior to the quantization.

15. A method for converting an input compressed video bitstream into an output compressed video bitstream, comprising the steps of:

(a) applying a process to convert the input bitstream into the output bitstream;

(b) generating one or more input measurements from the input bitstream;

(c) generating one or more output measurements from the output bitstream; and

(d) comparing the one or more input measurements to the one or more output measurements to generate one or more control parameters that are used to adjust the process so that subsequent output measurements will more closely match subsequent input measurements, wherein;

the one or more input measurements includes arrival margin of frames in the input bitstream;

the one or more output measurements includes arrival margin of frames in the output bitstream; and

the arrival margins of corresponding frames in the input and output bitstreams are compared to generate the one or more control parameters that are used to adjust the process so that subsequent output arrival margins will more closely match subsequent input arrival margins.

16. The invention of claim 15, wherein step (a) comprises the steps of:

(1) at least partially decoding the input bitstream to generate at least partially decoded video data;

(2) applying image processing to the decoded video data to alter imagery represented in the decoded video data; and

(3) re-encoding video data corresponding to the decoded video data to generate the output bitstream, wherein the one or more control parameters are used to adjust the re-encoding.

17. A method for converting an input compressed video bitstream into an output compressed video bitstream, comprising the steps of:

(a) applying a process to convert the input bitstream into the output bitstream;

(b) generating one or more input measurements from the input bitstream;

(c) generating one or more output measurements from the output bitstream; and

(d) comparing the one or more input measurements to the one or more output measurements to generate one or more control parameters that are used to adjust the process so that subsequent output measurements will more closely match subsequent input measurements, wherein;

the one or more input measurements includes actual bitcount of frames in the input bitstream;

the one or more output measurements includes actual bitcount of frames in the output bitstream; and

the actual bitcounts of corresponding frames in the input and output bitstreams are compared to generate the one or more control parameters that are used to adjust the process so that subsequent output arrival margins will more closely match subsequent input arrival margins.

18. A method for converting an input compressed video bitstream into an output compressed video bitstream, comprising the steps of:

(a) applying a process to convert the input bitstream into the output bitstream;

(b) generating one or more input measurements from the input bitstream;

(c) generating one or more output measurements from the output bitstream; and

(d) comparing the one or more input measurements to the one or more output measurements to generate one or more control parameters that are used to adjust the process so that subsequent output measurements will more closely match subsequent input measurements, wherein;

the one or more input measurements includes picture durations in the input bitstream;

the one or more output measurements includes picture durations in the output bitstream; and

the corresponding picture durations in the input and output bitstreams are compared to generate the one or more control parameters that are used to adjust the process so that subsequent output arrival margins will more closely match subsequent input arrival margins.