Video size conversion and transcoding from MPEG-2 to MPEG-4

• US 6,647,061 B1
• Filed: 06/09/2000
• Issued: 11/11/2003
• Est. Priority Date: 06/09/2000
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: General Instrument Corporation (CommScope Holding Company, Inc.)
• Inventors: Panusopone, Krit, Chen, Xuemin
• Primary Examiner(s): LEE, Y YOUNG
• Application Number:
  US09/590,928
• Time in Patent Office: 1,250 Days
• Field of Search: H04/N.712, 375/240.01, 375/240.02, 375/240.03, 375/240.12, 375/240.13, 375/240.16, 375/240.18, 375/240.2, 375/240.21, 375/240.24, 375/240.26, 375/240.29, 382/232, 382/235, 382/236, 382/238, 382/239, 382/248, 382/250, 382/251
• US Class Current: 375/240.12
• CPC Class Codes: H04N 19/105 Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for prediction
• CPC Class Codes: H04N 19/112 according to a given display mode, e.g. for interlaced or progressive display mode
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/137 Motion inside a coding unit, e.g. average field, frame or block difference
• CPC Class Codes: H04N 19/196 being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters processing of motion vectors H04N19/513
• CPC Class Codes: H04N 19/198 including smoothing of a sequence of encoding parameters, e.g. by averaging, by choice of the maximum, minimum or median value
• CPC Class Codes: H04N 19/20 using video object coding
• 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 19/59 involving spatial sub-sampling or interpolation, e.g. alteration of picture size or resolution
• CPC Class Codes: H04N 19/70 characterised by syntax aspects related to video coding, e.g. related to compression standards
• CPC Class Codes: H04N 21/234309 by transcoding between formats or standards, e.g. from MPEG-2 to MPEG-4 or from Quicktime to Realvideo conversion of standards in analog television systems H04N7/01
• CPC Class Codes: H04N 21/23439 for generating different versions
• CPC Class Codes: H04N 21/23608 Remultiplexing multiplex streams, e.g. involving modifying time stamps or remapping the packet identifiers

Abstract

A transcoder architecture that provides the lowest possible complexity with a small error, e.g., for converting an MPEG-2 bitstream into an MPEG-4 bitstream. The transcoder reads header information from an input bitstream and provides a corresponding header in the new format for the output bitstream. In one embodiment, a low complexity front-to-back transcoder (with B frames disabled) avoids the need for motion compensation processing. In another embodiment, a transcoder architecture that minimizes drift error (with B frames enabled) is provided. In another embodiment, a size transcoder (with B frames enabled) is provided, e.g., to convert a bitstream of ITU-R 601 interlaced video coding with MPEG-2 MP@ML into a simple profile MPEG-4 bitstream which contains SIF progressive video suitable for a streaming video application. For spatial downscaling of field-mode DCT blocks, vertical and horizontal downscaling techniques are combined to use sparse matrixes to reduce computations.

Claims

1. A method for transcoding a pre-compressed input bitstream that is provided in a first video coding format, comprising the steps of:

recovering header information of the input bitstream;

providing corresponding header information in a second, different video coding format;

partially decompressing the input bitstream to provide partially decompressed data; and

re-compressing the partially decompressed data in accordance with the header information in the second format to provide an output bitstream wherein the first video coding format comprises MPEG-2 Main Profile at Main Level; and

the second video coding format comprises an MPEG-4 bitstream with Standard Intermediate Format (SIF) progressive video.

2. The method of claim 1, wherein:

the first and second video coding formats comprise an MPEG-2 format and an MPEG-4 format, respectively.

3. The method of claim 1, wherein:

the partially decompressed data comprises motion vectors and Discrete Cosine Transform (DCT) coefficients; and

the second format comprises at least one of a new mode decision, AC/DC prediction, and motion compensation.

4. The method of claim 1, wherein:

at least one look-up table is used to provide the corresponding header information in the second video coding format.

5. The method of claim 1, wherein:

downscaling is performed on the partially decompressed data by downsampling DCT coefficients and motion vector data thereof.

6. The method of claim 1, wherein:

2;

1 downscaling is performed on at least one group of four field-mode Discrete Cosine Transform (DCT) blocks of the partially decompressed data by performing vertical downsampling and de-interlacing thereto to obtain a corresponding group of two frame-mode DCT blocks, and performing horizontal downsampling to the two frame-mode DCT blocks to obtain one frame-mode DCT block.

7. The method of claim 6, wherein:

the vertical downsampling also achieves low pass filtering of the four field-mode DCT blocks.

8. The method of claim 6, wherein:

the vertical and horizontal downsampling use respective sparse matrixes.

9. The method of claim 1, wherein:

in the recompressing step, a code (DQUANT) which specifies a change in a quantizer is set according to a differential value of a quantization parameter of the partially decompressed data.

10. The method of claim 1, wherein:

for re-compressing intra coded macroblocks, a coded block pattern (CBP) is set according to a corresponding value of the partially decompressed data.

11. The method of claim 1, wherein:

for re-compressing non-intra coded macroblocks, skipped macroblocks in the partially decompressed data are coded as not_coded macroblocks, where all Discrete Cosine Transform (DCT) coefficients have a zero value.

12. The method of claim 1, wherein:

in the recompressing step, predicted motion vectors in the partially decompressed data are reset according to the second format.

13. The method of claim 1, wherein:

in the recompressing step, dual prime mode macroblocks of the partially decompressed data are converted into field-coded macroblocks.

14. An apparatus for transcoding a pre-compressed input bitstream that is provided in a first video coding format, comprising:

means for recovering header information of the input bitstream;

means for providing corresponding header information in a second, different video coding format;

means for partially decompressing the input bitstream to provide partially decompressed data; and

means for re-compressing the partially decompressed data in accordance with the header information in the second format to provide an output bitstream wherein the first video coding format comprises MPEG-2 Main Profile at Main Level; and

the second video coding format comprises an MPEG-4 bitstream with Standard Intermediate Format (SIF) progressive video.