Television – Nonpictorial data packet in television format
Reexamination Certificate
1999-09-13
2004-02-10
Lee, Michael H. (Department: 2614)
Television
Nonpictorial data packet in television format
C348S473000, C348S478000, C348S479000, C348S423100, C348S462000
Reexamination Certificate
active
06690428
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for embedding digital audio data in a serial digital video data stream.
SMPTE 259M-1993 (hereinafter referred to simply as SMPTE 259) defines the serial digital interface (SDI) signal format for video. In accordance with SMPTE 259, video is transmitted as 8-bit or 10-bit serial data at 143, 177, 270 or 360 Mb/s.
The SDI signal format allows a user of equipment that supports this standard to interconnect discrete items of equipment with the assurance that the different items are compatible with respect to the form in which video data is supplied or received by the respective items.
The SDI signal format specifies locations at which ancillary data can be accommodated in the field of a composite digital signal or a component digital signal. For convenience and brevity, the following description will focus on component digital signals. Much of the description is also applicable directly to composite digital signals. Those skilled in the art will recognize where the description is not applicable to composite digital signals and will understand how the description should be modified to render it applicable to composite digital signals.
ANSI S4.40 prescribes a data stream for digital audio data. The data stream, which is known as the AES-3 data stream, or simply the AES data stream, is composed of a succession of frames, each frame containing two subframes and each subframe containing 32 bit cells. Subframe
1
contains an audio data sample for audio channel
1
and subframe
2
contains an audio data sample for audio channel
2
. The two channels of the AES data stream may be, but need not be, related, for example as left and right stereo channels. Referring to
FIG. 1
, each subframe contains a preamble of
4
bit cells, 4 bits of auxiliary data, 20 bits of sample data and 4 additional bits, which are referred to as V (validity), U (user), C (channel status) and P (parity). The four bits of auxiliary data may be used as added sample data space, allowing 24-bit samples, although the usual sample is 20 bits.
SMPTE 272M-1994 (hereinafter referred to simply as SMPTE 272) defines the mapping of AES digital audio data into the horizontal ancillary data, or HANC, space of the SDI data stream, resulting in a serial data stream including both video data and audio data. The horizontal ancillary data space has a preset range of word locations for ancillary data: for example, in the case of the component digital SDI signal format based on 525 lines, 29.97 frames per sec, the word locations are 1444-1711.
At the preferred 48 kHz audio sample rate, there are 1920 samples during one frame interval of a video signal having a 25 Hz frame rate and 1601.6 samples during one frame interval of a video signal having a 29.97 Hz frame rate. Thus, there are 3.072 audio samples per line interval for a 625 line, 25 Hz video signal and 3.051 audio samples per line interval for a 525 line, 29.97 Hz video signal. In order to provide a uniform distribution of audio samples throughout the frame of the composite audio-video data stream, three samples are placed in the HANC space of most lines of the video signal and four samples are placed in other lines. SMPTE standards specify that there should be no samples in the HANC space immediately following the switch line.
In accordance with SMPTE 272, sample data for one audio group, consisting of one or two AES digital audio data streams (each having two channels), is used to construct an audio data packet (or base packet) which is inserted in the HANC space on a given line. Referring to
FIG. 2
, in the case of digital composite video the first four words of the base packet are a data header, data ID, data block number and data count. There are then two or four channels, each containing an unspecified number of sets of three consecutive sample data words X, X+1 and X+2 (subject to a maximum of 255 user words). The final word of the base packet is a check sum. In the case of digital component video, the data header is three words long, but the structure of the base packet is otherwise the same.
The channels are organized in a sequence (e.g. 1, 2, 3, 4 in the case of four channels) and the sequence of channels repeats in the SMPTE 272 packet a number of times equal to the number of audio samples (typically three or four) to be accommodated by the SMPTE 272 packet. Each set of three consecutive sample data words X, X+1, X+2 represents one audio data sample.
A single data sample for one AES channel is derived from the 20 bits of sample data and the V, U and C bits of one AES subframe, and these twenty-three bits are mapped into the three consecutive sample data words X, X+1, X+2 of one channel of the SMPTE 272 packet. In the case of a group containing four channels, there are 36 sample data words (three samples*three words per sample*four channels) in the audio data packet if the packet contains three samples and there are 48 sample data words in the packet if the packet contains four samples.
The auxiliary data of two AES data streams of one audio group may be used to construct an extended data packet to be inserted in the HANC space on the same line as the base packet. The extended data packet is composed of a data header (one word or three words depending on whether the digital video is composite or component), data ID (one word), data block number (one word), data count (one word), an unspecified number of auxiliary data words, and a check sum (one word). The auxiliary data bits of the two AES subframes of one AES frame are mapped into one auxiliary data word of the extended data packet. The extended data packet for a given group immediately follows the base packet for that group and the number of auxiliary data words must match the number of samples in the base packet.
The ancillary data space of the SDI signal derived from a digital composite video signal is able to accommodate only one group (four digital audio channels, corresponding to two AES streams), whereas the ancillary data space of the SDI signal derived from a digital component video signal is able to accommodate four groups (sixteen digital audio channels, corresponding to eight AES streams). On each line that contains ancillary data, there is a base packet for each group and there is also an extended data packet for any group containing an AES data stream that includes auxiliary data.
The data ID of the base packet and extended data packet reflects the number of the group to which the two AES streams used to form the packets have been assigned.
Under SMPTE RP 165, an EDH (error detection and handling) packet may be included in the HANC space of one line per field. The EDH packet is inserted at the end of the HANC space. The embedder must take care to ensure that the EDH packet is not overwritten by audio packets, particularly in the case of the 270 Mb/s format where the HANC space is not large enough to support four groups of data with four samples per group as well as the EDH data.
In accordance with SMPTE 272, if a signal includes horizontal ancillary data, the ancillary data must start immediately after the EAV (end of active video) timing reference signal and all packets of ancillary data must be contiguous. Accordingly, there should be no ancillary data in the HANC space after the start of blanking.
A conventional device for embedding an audio group in an SDI video data stream operates by constructing the base packets (20 bits of audio data) and multiplexing the base packets into the digital video data stream immediately after the EAV timing reference signal. At the receiving end, the receiver detects the header of the audio data packet and controls a demultiplexer which extracts the ancillary data from the data stream, allowing the AES subframes to be reconstructed.
If the video data stream is able to accommodate more than one group, conventional embedders operate in cascade fashion. Thus, in the event that sixteen channels are to be embedded, a first embedder receives both the SDI data stre
Hudelson Robert W.
Lydon Donald S.
Meyer Charles S.
Desir Jean W.
Lee Michael H.
NVISION, Inc.
Smith-Hill John
Smith-Hill and Bedell
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