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Establishing Correspondence Between Source-based Video Time and Zero-Based Video Time in Digital Video

IP.com Disclosure Number: IPCOM000015915D
Original Publication Date: 2002-Jun-01
Included in the Prior Art Database: 2003-Jun-21
Document File: 4 page(s) / 54K

Publishing Venue

IBM

Abstract

Background

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  Establishing Correspondence Between Source-based Video Time and Zero-Based Video Time in Digital Video

Background

There are worldwide a very large number of analog videotapes. These tapes may be in old formats (reel-to-reel), they may be gradually deteriorating, and they may be hard to access because of the inherent sequential nature of tape. Digitizing these tapes solves all these problems.

However, if these tapes have timecodes, these may or may not be carried forward when they are digitized.

Tape may or may not have time codes. Digitizer may or may not be able to read time codes. Digitizer may be able to read time codes, but person digitizing elects not to transfer the timecodes to the digitized file or elects a format for the digitized file that cannot hold time codes.

Moreover a given player that the user has available may not be able to read time codes in digitized file.

Finally, if a tape is digitized to not one but several formats, some of these formats may preserve timecodes while others may not.

Problem

When timecodes are no longer available for any of the reasons above, some correspondence must be made between the timecodes on the original tape and the digitized file with no timecodes, which starts at a time of zero. Only this way can frames in the digitized file be matched to timecodes of frames on the original tape. Suppose for example we know that there is a scene change on the tape at a certain timecode. We must convert that timecode to a time starting at zero to find the scene change in the digitized file.

The hard parts of this problem, which are solved here is the combination of difficulties that arise because timecodes as a standard for time display cannot exceed 24 hours:

A tape with timecodes that start at a high value and goes up from there wraps around at

24 hours to zero followed by small values of time as the tape proceeds. Timecodes cannot exceed 24 hours even as temporary values during computations,

because then they would not be legitimate timecodes. This can occur for example making an API call for each + and - in the computation, where the API receives two timecode values to add or subtract and returns a timecode result. Obviously each result must be a legitimate timecode bound by the 24-hour limit.


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Solution

We simultaneously compensate for the first difficulty and order the computation to avoid the second difficulty.

Source-based timecodes are codes that are embedded in video tape giving the time and frame number of each frame. Each frame of video has an associated time code written along side it.

SMPTE format is often used to display timecodes. SMPTE format is HH:MM:SS:FF, two digits each for hours, minutes, seconds, and frame number (

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http://www.etcconnect.com/html/service_smpte.html ).

Zero-based time codes begin at 0 for the first frame. This first frame may correspond to some non-zero source-based time code written on that frame. The difference between the two establishes the...