2/24/2008 9T6WP
Preliminary Hardware Data Module
BCM7405
06/29/07
Functional Description
Bro a d c o m Co rp o r a ti o n
Document
7405-1HDM00-R
Video Data Flow
Page 1-9
P
ERSONAL
V
IDEO
R
ECORDING
Processing of compressed streams for Personal Video Recording (PVR) extends the normal processing by adding a number
of capabilities. In recording for PVR, the transport packets associated with the program selected are recorded to a circular
buffer in DRAM for transfer to the hard disk drive (HDD). The compressed data is optionally scrambled using the mem-to-
mem security block. In addition, the video elementary stream (ES) data contained within the selected PID is searched for
the presence and location of selected start codes, such as PES packet headers, sequence start codes, picture start codes,
and the first slice start codes within each picture. Sufficient data from the compressed streams following the start codes is
also retained to determine the picture type (I, B, or P) and other pertinent information. All of this selected information is written
to memory in a circular buffer to facilitate additional processing by the Host MIPS as required, and to record the data to the
HDD. The PES packets can be recorded as an alternative to Transport streams.
In PVR playback, the transport processor reads linked lists of compressed audio and video from DRAM, optionally
descrambling it using mem-to-mem security block, and processes it for decompression and display in a manner that is similar
in many ways to normal (non-stored) decoding. The PVR playback supports special capabilities for fast and slow decoding
and descrambling, and data flow management in the absence of a physical time base associated with the stream (as would
normally be present in broadcast operation).
D
IGITAL
V
IDEO
D
ECOMPRESSION
Decompression of digital video is performed by the AVC/MPEG-2/VC-1 processor. The decoder extracts compressed video
and index tables from DRAM (created by the data transport). The video is decoded or decompressed and the resultant is
stored back into DRAM in picture (frame or field) buffers in YCrCb 4:2:0 format. The decoder needs multiple picture buffers
to account for differing time bases and decode rates.
ITU-R 656 I
NPUT
The BCM7405 supports an ITU-R 656 video input. The input has a dedicated VBI decoder to handle Teletext, NABTS, Close
Caption, CGMS-A, Gemstar, and WSS.
V
IDEO
P
ROCESSING
The display engine takes in uncompressed video from either the AVC/MPEG-2/VC-1 decoder or the digital ITU-R-656 input.
The display engine can scale the video in horizontal and vertical directions and either display the video immediately (in-line)
or capture it to memory for later viewing. Scaling is optional, and may be needed for normal display of digital or analog video.
The scaling function incorporates a format conversion capability for converting between various standard definition (SD) and
HD formats of video signals and those required by the displays. Capture of video to memory is used either when it is
advisable to minimize peak DRAM bandwidth requirements, or when it is unavoidable due to the constraints of the video
input and output timing. In general, capturing to memory when scaling reduces peak DRAM bandwidth when the scale factor
is less than 1.0. The video and graphics processing is further expanded in
“Video and Graphics Display” on page 1-36
.