Browse Prior Art Database

Simple Synchronization Method for Real-Time Video Codecs on Multimedia Adapters

IP.com Disclosure Number: IPCOM000117189D
Original Publication Date: 1996-Jan-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 161K

Publishing Venue

IBM

Related People

Potu, B: AUTHOR

Abstract

Synchronizing real-time video stream with a Video Codec is essential for capturing video data after compression and playing back compressed data after decompression. If the synchronization is lost in capture operation, a compressed video frame data might contain parts of more than one video frame. If the synchronization is lost during playback, tear artifacts will be clearly visible over the display due to data from multiple frames displayed in a single frame.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 41% of the total text.

Simple Synchronization Method for Real-Time Video Codecs on Multimedia
Adapters

      Synchronizing real-time video stream with a Video Codec is
essential for capturing video data after compression and playing back
compressed data after decompression.  If the synchronization is lost
in capture operation, a compressed video frame data might contain
parts of more than one video frame.  If the synchronization is lost
during playback, tear artifacts will be clearly visible over the
display due to data from multiple frames displayed in a single frame.

      The Codec interface in a typical video capture and playback
adapter is shown in Fig. 1.  The interface consists of a live video
I/O data path to filed memory to store digital video component data.
A high-speed strip buffer converts the video data that is in scan
format to blocked video format required by the Codec.  The Codec
writes data to the output buffer during capture/compression operation
and reads data from the output buffer during playback/decompresion
operation.

      Prior art seems to be a simple synchronization scheme to
capture a field of video into the field memory and compress it and
then capture another field to field memory and compress it and so on.
Serializing the operation in such a manner does produce tear-free
capture.  However, it is inefficient as there will be large number of
skipped fields during the capture operation and the Codec would not
be operating at its peak performance.  A similar scenario occurs
during playback operation.

      Synchronization logic with an 8-bit up/down counter and a
configuration register ware used on the Ultimedia Video I/O and Joint
Photographics Experts Group standard (JPEG) adapter to produce
tear-free video capture and playback.  The simple logic forces the
Codec to operate at its peak performance reducing the number of
skipped fields during capture and playback operation.  The Codec
speed, and not the synchronization issues dictate the capture and
playback performance.  Ultimedia Video I/O and JPEG adapter has a
JPEG engine, CL550 to perform video compression and decompression.

      The configuration register contains three bits to control the
operation of the bidirectional video data I/O between the Codec and
the field memory.  The register is programmable and can be changed
for capture and playback operations independently.  The first bit,

Fr/F represents either Frame or Field, the second bit, E/O represents
even or odd field, and the third bit, F/C represents a full-size
image or a CIF size image that needs be compressed or decompressed.

      The Codec is completely asynchronous with the real-time video
stream on the Video I/O bus operating at different clock frequencies.
Usually the Codec's clock speed is higher to get a good performance.
The only controllable element in the whole system is STALL signal
input of the Codec.  When the signal is asserted the pipeline inside
the Codec on the...