Method and apparatus for reproducing at a selected speed video signals recorded on magnetic tape

• US 5,223,987 A
• Filed: 06/27/1990
• Issued: 06/29/1993
• Est. Priority Date: 07/06/1989
• Status: Expired due to Fees

• Current Assignee: BTS Broadcast Television Systems GmbH A Limited Liability Company of The FED REP Germany
• Original Assignee: BTS Broadcast Television Systems GmbH (Koninklijke Philips N.V.)
• Inventors: Muller, Jurgen
• Primary Examiner(s): Psitos, Aristotelis
• Assistant Examiner(s): KAPADIA, VARSHA A
• Application Number:
  US07/544,742
• Time in Patent Office: 1,098 Days
• Field of Search: 360/14.1, 360/14.2, 360/14.3, 360/72.2, 360/10.3, 360/10.1, 360/33.1, 358/311, 358/335, 358/314
• US Class Current: 386/343
• CPC Class Codes: H04N 5/783 Adaptations for reproducing at a rate different from the recording rate
• CPC Class Codes: H04N 5/937 by assembling picture element blocks in an intermediate store
• CPC Class Codes: H04N 5/945 for signals recorded by pulse code modulation
• CPC Class Codes: H04N 5/956 by using a digital memory with independent write-in and read-out clock generators

Abstract

The magnetic tape video playback apparatus for a digital video signal regenerates the sample rate from the playback to operate a counter and detects the video data block numbers to permit an address generator to derive the more significant bits of addresses for a picture memory in which the video data signal is temporarily stored. The counter provides the less significant bits of the write addresses. The separated vertical sync pulses are counted in a second counter to provide time information for storage in a time data memory which is operated in parallel with the picture memory, using the write addresses from the already mentioned address generator. A reference sample rate generator operates a third counter which provides the read out addresses for the picture and time data memories. The memory input and output time data are compared and the time difference is evaluated with reference to a threshold for providing an error flag to an error concealment unit to which the video data read out from the picture memory is supplied for concealing errors resulting from overage video data in the picture memory which may be stored there during playback at high speeds. At low speeds the minimum time difference designates an error.

Claims

1. A method of playing back video signals recorded on a magnetic tape in a video tape equipment in which the playback speed is variable, with reference to the speed at which the video signals were recorded, and wherein picture filed video data of recorded video data blocks are written into a picture memory which is addressed in part by video data block identifying information included in recorded video data blocks, and subsequently read out from said picture memory, characterized in that:

concurrently with the writing of said picture field video data in said picture memory (4) a parallel operation is performed of writing current time information into a time data memory at addresses corresponding to the concurrent addressing of picture field video data in said picture memory;

in that concurrently with the reading out of picture field video data from said picture memory (4), time information previously written in is read out from said time data memory (6);

in that said time information read out of said time data memory (6) is compared with the current time information available for input into said time data memory (6), and the time difference result of said comparison, if it exceeds a predetermined time difference magnitude, is utilized to designate video data being concurrently read out from said picture memory (4) as suitable for immediate treatment as erroneous video data;

in that said video signals are digital and are recorded in groups each subdivided into numbered blocks of uniform size;

in that addresses for addressing said picture and time data memories are derived form block numbers relating to individual blocks, and

in that detailed time information for writing into said time data memory at appearances of successive block numbers is derived from counting equal increments of time and said counting is started by a vertical synchronizing signal pulse played back from said tape and, after overflow of counting, restarted by another vertical synchronizing signal pulse played back from said tape.

2. The method of claim 1 wherein a first predetermined time difference magnitude is utilized to designate erroneous video data being concurrently read out during playback at a tape speed exceeding the tape speed at which said video data was recorded and a second predetermined time difference magnitude is utilized to designate as erroneous video data being concurrently read out during playback operation at a tape transport speed which is equal to or lower than the tape transport speed at which video data was recorded on said tape.

3. The method of claim 1, wherein an error concealment procedure is performed on some video data designated as erroneous by a criterion of time comparison.

4. Apparatus for playback of a tape recorded digital video data signal from a magnetic tape driven at a selectable playback tape speed, said apparatus having a variable speed tape drive, a rotary device equipped with playback magnetic heads for scanning said tape obliquely to its direction of movement, means for subjecting the output of said playback magnetic heads to preamplification, distortion compensation, synch pulse separation and video data block number detection to produce a processed video data signal for temporary storage, means for deriving sample rate clock pulses from said output of said playback magnetic heads, and picture memory means (4) for storing said processed video data signal, and further comprising:

a first counter (8) connected for counting equal time increments and connected to said synch pulse separation means for starting time increment counting in response to a pulse of a vertical synchronizing signal and for restarting after an overflow of said first counter, in response to another pulse of said vertical synchronizing signal, said first counter (8) having a multi-bit output for a time signal produced by counting said time increments;

a first address generator (5) having an input connected to said video data block number detection means for deriving more significant bits of a write-in address signal for said picture memory means (4) from said detected block numbers and having an output;

a second counter (7) connected for supplementing said first address generator in less significant bit addressing of said picture memory means (4) and connected for counting said sample rate clock pulses supplied by said mean for subjecting the output of said playback magnetic heads to preamplification, distortion compensation and synch pulse separation;

a second address generator (10) connected to a source (11) o timing reference signals for deriving a read address signal for said picture memory means from said reference signals and having an output;

a time information random-access memory (6) having a multi-bit data input connected to said multi-bit output of said first counter (8) and having a write-in address input connected with said output of said first address generator (5) for receiving therefrom a plurality of more significant bits of said write-in address signals and read address inputs connected with outputs of said second address generator (10) for receiving therefrom a plurality of more significant bits of said read address signal, said time information memory having a read-out output for time data signals;

an error flag generating stage (12) having means for determining magnitude and presence of a time difference between a time signal being written into said time data memory from said output of said first counter and a time data signal being read out from said output of said time data memory, including means for producing an error flag output whenever said time difference exceeds a predetermined time difference magnitude;

electrical connection means for providing said output of said first address generator (5) and a count content output of said second counter (7) to write-in address input of said picture memory means (4);

p1 electrical connection means for providing outputs of said second address generator (10) to read address inputs o said picture memory means, and

error concealment mans (9) having a video data signal input connected for receiving video data read out from said picture memory means (4) and a control input connected to said error flag output of said error flag generating stage and having a video data signal output.