Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
2000-12-01
2004-12-07
Tran, Thai (Department: 2616)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000, C386S349000, C386S349000, C348S468000
Reexamination Certificate
active
06829429
ABSTRACT:
This application is based on an application No. H11-343528 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a video recording device for recording a video signal which includes character information such as closed caption data, and in particular relates to a technique of recording character information together with video information.
2. Prior Art
A video recording device equipped with a time base corrector (hereinafter, “TBC”) is conventionally used to receive analog video signals outputted from a TV broadcaster or a video recorder on a frame-by-frame basis, convert the received analog video signals to digital video signals, and record them onto a recording medium such as a DVD.
In general, when converting an analog video signal to a digital video signal and recording it, the receive frequency of the video signal and the clock frequency which defines the timing of recording the video signal onto a recording medium (hereinafter, “reference frequency”) do not synchronize precisely. This being so, when video signals are sequentially being written into an internal memory of the video recording device in accordance with the receive frequency and then being read from the internal memory and recorded onto the recording medium in accordance with the reference frequency, the amount of data flowing into the memory and the amount of data flowing from the memory become unbalanced, which often causes the memory to underflow or overflow.
To avoid this and enable seamless recording of data, the TBC operates to monitor the occurrence of underflow and overflow in the memory, and smooth out discrepancies between the video signal recording speed defined by the reference frequency which is fixed and the video signal input speed determined by the receive frequency which could vary, by repeating or skipping an output of a video signal from the internal memory in units of video frames. In so doing, the balance between the amount of incoming data and the amount of outgoing data in the memory is maintained.
To be more specific, when the receive frequency is higher than the reference frequency, the amount of incoming data exceeds the amount of outgoing data per unit time. In this case, the TBC skips a one-frame video signal and outputs the next one-frame video signal from the memory. On the other hand, when the receive frequency is lower than the reference frequency, the amount of incoming data falls short of the amount of outgoing data per unit time. In this case, the TBC outputs a one-frame video signal which was once outputted, again.
FIG. 1
shows how the TBC repeats or skips an output of a one-frame video signal.
In the figure, each large box represents a one-frame video signal which includes video information for video display and character information for character display.
The video information is designated by an alphabet that identifies the video signal, to indicate the flow of the video signal being written into or read from the memory.
The character information (explained later) is designated by alphabets that show characters contained in two types of character information included in the video signal. The uppercase alphabetic characters and the lowercase alphabetic characters respectively correspond to the two types of character information.
In each video signal shown in the middle of the figure, the alphabet given above the forward slash mark “/” indicates data which is read from the memory in the case where the receive frequency is higher than the reference frequency (t
1
<t
0
, t
0
=1/(reference frequency)), whereas the alphabet given under “/” indicates data which is read from the memory in the case where the receive frequency is lower than the reference frequency (t
2
>t
0
).
In the figure, the direction from left to right represents time, with the reference line of each frame with respect to time is indicated by the left side line.
The operation of the TBC is explained below, with reference to this figure.
Unless the video signal receive frequency keeps perfect synchronization with the reference frequency, the amount of data flowing into the memory and the amount of data flowing from the memory will eventually become unbalanced, thereby causing an overflow or an underflow in the memory.
To prevent a memory overflow (in the case of t
1
<t
0
), the TBC skips the reading of the one-frame video signal “D” (see X
1
in FIG.
1
), and instead reads the next one-frame video signal “E” from the memory. To prevent a memory underflow (in the case of t
2
>t
0
), the TBC reads the one-frame video signal “A” twice from the memory (see X
2
in FIG.
1
).
In recent years, a caption display technique called closed captioning has been developed to display a caption of actors' lines, narrations, and sound effects so that the hearing impaired can enjoy broadcast programs and videos. In the closed caption technique, character information for caption display is multiplexed on a video signal so as to display a caption in sync with a video.
Also, similar caption display techniques have been developed that display information other than closed captions, such as weather forecast information, time information, and stock price information, by multiplexing these information on a video signal. Nowadays these techniques are put into actual use as well as the closed captioning.
Consequently, a video signal which usually contains only video information comes to contain character information such as closed caption data, when these caption display techniques are employed.
Such character information is carried on line
21
in both fields of the video signal, i.e. the vertical interval which is not used for picture display.
To display such character information on a screen, a decoder for decoding the character information multiplexed on the video signal is needed. A viewer can decide whether to display the character information or not.
However, the aforementioned caption display techniques have the following problem.
Video information corresponding to one frame is visual information of approximately 29.97 msec. A dropout or overlap of such one-frame video information is unlikely to cause visual disturbances. However, the problem arises when the TBC skips or repeats recording of character information corresponding to one frame, in the same way as video information. Character information is made up of character codes such as ASCII (American Standard Code for Information Interchange) codes and special character codes. Suppose character information representative of the characters “A, B”, “C, D”, “E, F”, “G, H”, “I, J”, . . . is sequentially inputted into the memory as closed-caption data, as shown in FIG.
1
. Here, if the receive frequency is higher than the reference frequency, the character information is recorded in the order of “A, B”, “C, D”, “E, F”, “I, J”, . . . , where the character information “G, H” is skipped. If, on the other hand, the receive frequency is lower than the reference frequency, the character information is recorded in the order of “A, B”, “A, B”, “C, D”, “E, F”, . . . , where the character information “A, B” is recorded twice. Thus, when the TBC is used to record character information multiplexed on video signals, dropouts or overlaps of characters are likely to occur. Character information recorded in such a way will end up being unintelligible to a viewer.
SUMMARY OF THE INVENTION
In view of the above problem, the first object of the invention is to provide a video recording device that, when recording a video signal containing character information using a TBC, can record the character information as faithfully as possible.
The second object of the invention is to provide a video recording method that realizes the faithful recording of the character information.
The third object of the invention is to provide a video rate adjusting device that outputs a video signal for enabling the faithful recording of the character information, the video rate adjusting d
Kitahashi Masaki
Nakamura Kazuhiko
Watanabe Yoshiyuki
Tran Thai
Vent Jamie
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