Koninklijke Philips Corporation N.v.

U.S. Philips Corporation

Nicolas Bailleul

Etienne Fert

Pierre Gautier

Johan Cornelis Talstra

Johan P M G Linnartz

Antonius A C M Kalker

Myriam Grandchamp

An MPEG video stream generator, which contains several slightly different programs, each with approximately the same content. The MPEG stream is constructed in such a manner that a simple transcoder can effectively select one of the programs. This is achieved by storing the differences relative to the default program in selected user data fields. The transcoder is little more than an MPEG bitstream parser, which replaces the bits corresponding to selected set of macroblocks by the replacement data stored in the user data fields. A standard MPEG decoder without any knowledge of the embedded user data fields will simply extracted the default program. One application relates to broadcasting of a television program with or without a logo, or a commercial with or without a public warning. Another application relates to copy-protection schemes. In such a scheme, the default program contains a ticket indicating that the contents may be copied once. Upon recording, this ticket is removed and replaced by the content accommodated in the user data field.

Video signal transmission

By coding (ENC) data (D), coded data (CD) and, in addition, a set of parameters (PAR) for decoding (DEC) the coded data (CD) are obtained. MPEG video coding is an example of such a coding. The coded data (CD) is modified by carrying out the following steps. The coded data (CD) is, at least partially, decoded (DEC) so as to obtain decoded data (DD). The decoded data (DD) is modified (MOD) so as to obtain modified data (MD). The modified data (MD) is coded (ENC) so as to obtain coded modified data (CMD). It is examined (EXAM) whether a satisfactory result will be obtained if the set of parameters (PAR) for decoding the coded data (CD) is applied for decoding (DEC) the coded modified data (CMD). If the result is satisfactory, the set of parameters (PAR) for decoding the coded data (CD) is added to the coded modified data (CMD). If the result is not satisfactory, a new set of parameters (PAR) is established (ADP) and the new set of parameters (APAR) is added to the coded modified data (CMD). Accordingly, the coded data (CD) can be modified with relatively little distortion. An example of a modification which can be carried out in this manner is a 422/420 format conversion of MPEG-coded video.

Modifying coded data

Data (D) is compressed in dependence on a compression parameter (CPAR). An example of such data compression is coding a sequence of pictures in accordance with a standard defined by the Moving Pictures Experts Group. In the process of compressing the data (D), the following three steps are repetitively carried out. In a prediction step (PRD), it is predicted, on the basis of an initial value (VALint) of the compression parameter (CPAR), which amount of compressed data Xprd will have been obtained at a future instant of time (Tfut). In an adaptation step (ADP), the initial value (VALint) is adapted on the basis of a difference (&Dgr;X) between the predicted amount of data (Xprd) and a desired amount of data (Xdes), so as to obtain an adapted value (VALadp) of the compression parameter (CPAR). In an application step (APL), the adapted value (VALadp) of the compression parameter (CPAR) is applied until a subsequent prediction step (PRD) followed by a subsequent adaptation step (ADP) is carried out. Such data compression yields a better quality in terms of loss of information.

Data compression

Bit-rate modification

Data compression assembly having several data-compression channels

A basic transcoder, that decodes an encoded data stream and re-encodes it, may be used for locally modifying data in said stream. Said modification is carried out by defining a predicted data stream on the basis of a given modifying data stream and adding to the decoded stream&mdash;between the decoding and re-encoding parts of the transcoder&mdash;the difference between the modifying data stream and the predicted one. In an improved implementation, the modifying data stream is preprocessed so that it may be obtained in the decoded data stream a local substitution of said modifying data to the decoded ones.

Method and device for modifying data in an encoded data stream

A data stream (DS) comprises a time multiplex of coded data (D) and control data (C). The data stream (DS) may be, for example, of the MPEG type representing a sequence of pictures. The coded data (D) is transcoded (T) so as to obtain transcoded data (DT) which differs in size from the coded data (D). The control data (C) is adapted for the transcoded data (DT) so as to obtain adapted control data (CA) which does not substantially differ in size from the control data (C). The transcoded data (DT) and the adapted control data (CA) are written into a transcoder output buffer (TOB) and read from the transcoder output buffer (TOB) so as to obtain a transcoded data stream (DST). This allows an efficient use of a transmission channel via which the transcoded data stream (DST) is to be transmitted and, consequently, it allows a satisfactory transcoding quality. A size adjustment of the transcoded data (DT) on the basis of the amount of data contained in the transcoder output buffer (TOB) and control codes (CC) contained in the data stream (DS) further contributes to a satisfactory transcoding quality.

Transcoding of a data stream

Data (D), which has been coded by a coder (COD) so as to obtain coded data (CD), is modified. The data (D) may be, for example, a sequence of pictures which has been coded in accordance with an MPEG standard. The data (D), which is available in a coded form, is modified in the following manner. A partial decoder (PDEC) partially decodes the coded data (CD). That is, of a series of decoding steps (Sd(,) . . . Sd(N)) which need to be carried out in order to decode the coded data (CD), the partial decoder (PDEC) carries out only a first few decoding steps (Sd(,) . . . Sd(K)), with K and N being integers and K being smaller than N. Accordingly, partially decoded data (PDD) is obtained. A data-modifier (MOD) modifies the partially decoded data (PDD). Accordingly, modified partially decoded data (MPDD) is obtained. A complementary coder (CCOD) complementary codes the modified partially decoded data (MPDD). That is, the complementary coder (CCOD) carries out one or more coding steps (Sc(K) . . . Sc(,)), each of which is a complement (C) of a specific decoding step (Sd) which has been carried out by the partial decoder (PDEC). Accordingly, coded modified data (CMD) is obtained. Since only a partial decoding is carried out, fewer circuitry will be required than if the data (D) to be modified were fully decoded. Thus, the data (D) can be modified in a cost-efficient manner.

Modifying data which has been coded

A basic transcoder, that decodes an encoded data stream and re-encodes it, may be used for locally modifying data in said stream. Said modification is carried out by defining a predicted data stream on the basis of a given modifying data stream and adding to the decoded stream&mdash;between the decoding and re&mdash;encoding parts of the transcoder&mdash;the difference between the modifying data stream and the predicted one. In an improved implementation, the modifying data stream is preprocessed so that it may be obtained in the decoded data stream a local substitution of said modifying data to the decoded ones.

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Paris, France

Nicolas Bailleul