Abstract:
Methods, systems and computer-readable medium for changing video playback speed are disclosed. Video playback speed may be changed by determining a first frame rate and a second frame rate for which a frame rate transition is to be made. An instantaneous frame rate is calculated to produce a calculated instantaneous frame rate, wherein the calculated instantaneous frame rate is between the first frame rate and the second frame rate. A timestamp of a frame is adjusted based on the calculated instantaneous frame rate to produce an adjusted timestamp. Graphical data for the frame is provided in accordance with the adjusted timestamp to enable display of the frame. Thereafter, the frame may be displayed in accordance with the adjusted timestamp.

Description:
RELATED APPLICATIONS 
     The present application is a continuation application of and claims the benefit of U.S. patent application Ser. No. 09/994,428, filed Nov. 26, 2001 now U.S. Pat. No. 7,221,851, entitled “METHOD AND SYSTEM FOR DVD SMOOTH SEARCH TRANSITIONS,” naming James van Welzen, Brian Falardeau, and Jonathan White as inventors, assigned to the assignee of the present invention. That application is incorporated herein by reference in its entirety and for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     The DVD (digital versatile disk) format was designed by various members of the consumer electronics industry as a means of storing high quality audio-video content (e.g., a feature length film) on a single disk. To facilitate such efficient storage, the DVD format uses contemporary compression technologies to reduce the sizes of the video and audio bit streams comprising the content. 
     The DVD format employs the ISO MPEG-2 standard to compress video. MPEG-2 represents video content as a compressed series of frames. Each frame is a rectangular array of picture elements (pixels) depicting the content at a particular instant in time. Thus, playback consists of decompressing and then displaying this series of frames. 
     In conventional DVD players, the playback of DVD content is typically implemented in one of three ways: using dedicated hardware, using a software implementation, or using a combination of software and hardware. The most common or conventional implementation takes the form of a consumer electronics components with limited resources targeted exclusively at DVD playback. Less common or conventional implementations take the form of PC-based implementations or game consoles (e.g., Sony PLAYSTATION2, Microsoft X-BOX, etc.) which, because they target multiple functions, tend to have more extensive resources. 
     The MPEG-2 video standard employs three types of compressed frames: intra-frames (I-frames), predictive frames (P-frames), and bi-directionally predictive frames (B-frames). I-frames have no dependencies. Thus, an I-frame is self-contained and includes all information necessary to reproduce the associated original frame. P-frames may have forward dependencies, i.e., a P-frame is not self-contained. It may re-use information from the preceding decompressed reference frame (where a reference frame is either an I-frame or another P-frame). Thus, a playback implementation must decode reference frame preceding a P-frame before it decodes the P-frame itself and must keep the preceding reference frame resident in memory throughout the decoding of a P-frame. For the B-frames, B-frames are not self-contained and may have forward and backward dependencies, such that it may reuse information from either the preceding or the subsequent decompressed reference frame. Thus, a playback implementation must decode the reference frames both preceding and following a B-frame before it decodes the B-frame itself and must keep both the preceding and subsequent reference frames resident in memory throughout the decoding of a B-frame. 
     Normally, a playback implementation maintains four frame buffers (i.e., arrays of memory) of MPEG-2 video at any one time: 1) the currently decoded frame; 2) a forwards reference; 3) a backwards reference; and 4) the currently displayed frame. The forwards reference is the reference preceding the currently decoded frame, which is sometimes co-incident with the currently displayed frame. The backwards reference is the reference following the currently decoded frame. Additionally, the currently displayed frame is distinct from the currently decoded frame to prevent the player from updating a frame while it is being displayed, which causes an undesirable visual artifact called “tearing”. 
     Conventional DVD players have limited memory resources to reduce cost and enable forwards playback at normal speeds. However, the memory resources are insufficient for many fast-forwarding and rewinding operations. For example, conventional DVD players avoid decoding P or B frames when playing backwards, and instead only decode the self-contained I-frames. This leads to decoding less than 10% of the frames and providing jerky, low frame-rate play. 
     SUMMARY OF THE INVENTION 
     Accordingly, a need exists for improved video playback when performing fast-forwarding and rewinding operations. Embodiments of the present invention provide novel solutions to these needs and others as described below. 
     Embodiments of the present invention are directed to methods, systems and computer-readable medium for changing video playback speed. More specifically, video playback speed may be changed by determining a first frame rate and a second frame rate for which a frame rate transition is to be made. An instantaneous frame rate is calculated to produce a calculated instantaneous frame rate, wherein the calculated instantaneous frame rate is between the first frame rate and the second frame rate. A timestamp of a frame is adjusted based on the calculated instantaneous frame rate to produce an adjusted timestamp. Graphical data for the frame is provided in accordance with the adjusted timestamp to enable display of the frame. Thereafter, the frame may be displayed in accordance with the adjusted timestamp. 
     In one embodiment, the playback may comprise a smooth search transition (e.g., forward, backward, etc.). With the use of adjusted timestamps, the video playback appears as a smooth increase or decrease in playback speed (e.g., without the “jerk” associated with conventional systems) when transitioning between speeds (e.g., 0.5×, 1×, 2×, 4×, 8×, etc.). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements. 
         FIG. 1  illustrates a block diagram of a DVD player system with at least seven frame buffers in accordance with one embodiment of the present invention. 
         FIG. 2  illustrates an example of I-, P-, and B-frames representing an original sequence of 24 frames in accordance with one embodiment of the present invention. 
         FIG. 3  illustrates a block flow diagram for smooth reverse playback in the DVD player system in accordance with one embodiment of the present invention. 
         FIG. 4  illustrates an example step-by-step reconstruction diagram for the original sequence of frames in accordance with one embodiment of the present invention. 
         FIG. 5  illustrates a block flow diagram for a single frame backwards playback in accordance with one embodiment of the present invention. 
         FIG. 6  illustrates a block flow diagram for smooth frame search transitions in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. While the present invention will be discussed in conjunction with the following embodiments, it will be understood that they are not intended to limit the present invention to these embodiments alone. On the contrary, the present invention is intended to cover alternatives, modifications, and equivalents which may be included with the spirit and scope of the present invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, embodiments of the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention. 
     Notation and Nomenclature 
     Some portions of the detailed descriptions which follow are presented in terms of procedures, logic blocks, processing and other symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. In the present application, a procedure, logic block, process, or the like, is conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, although not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present invention, discussions utilizing the terms such as “accepting,” “accessing,” “adding,” “adjusting,” “analyzing,” “applying,” “assembling,” “assigning,” “calculating,” “capturing,” “combining,” “comparing,” “collecting,” “controlling,” “creating,” “defining,” “depicting,” “determining,” “displaying,” “distinguishing,” “establishing,” “executing,” “generating,” “grouping,” “identifying,” “modifying,” “moving,” “outputting,” “performing,” “placing,” “presenting,” “processing,” “programming,” “providing,” “querying,” “removing,” “repeating,” “sampling,” “sorting,” “storing,” “using,” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
     EMBODIMENTS OF THE INVENTION 
     The present invention provides aspects of displaying additional types of frames (e.g., in addition to I-frames) during the backwards playback in a DVD player. These aspects include smooth rewind, single frame stepping backwards, and smooth search transitions.  FIG. 1  illustrates a block diagram of a DVD player system for implementing the aspects of the present invention. Actual implementations of this DVD player include but are not limited to PC-based DVD players and game console-based DVD systems (e.g., Sony PLAYSTATION, Microsoft X-BOX, etc.). As shown in  FIG. 1 , the DVD player system includes a DVD drive (content storage)  100 , a decoding engine  102  (e.g., a CPU, etc.) for performing the processing of the present invention, an audio codec (audio rendering)  104 , audio amplifiers (audio medium)  106 , Memory  108  (e.g., comprising at least 7 video frame buffers), display controller (video rendering)  110 , and a display (visual medium) I 12 . In one embodiment, the at least 7 frame buffers are allocated either from system memory or the video memory of any resident graphics hardware, as is well appreciated by those skilled in the art. 
     Smooth Rewind 
     The DVD standard for the operation of the DVD player system prescribes that I-frames occur no less frequently than every 12 frames, as demonstrated by an example sequence of 24 original frames shown in  FIG. 2 . In accordance with the present invention, smooth backwards playback of such a sequence occurs as described with reference to the overall block flow diagram of  FIG. 3  and the step-by-step reconstruction diagram of  FIG. 4 . Referring to  FIG. 3 , to provide for the reverse playback from a currently displayed frame, reconstruction occurs from a last I-frame preceding a currently displayed frame to the frame immediately preceding the currently displayed frame (step  114 ). The process further includes utilizing at least 7 frame buffers to support the reconstruction (step  116 ). The data is displayed from memory in reverse order to provide a smooth playback of all the frames (step  118 ). 
     By way of example, for the process of  FIG. 3 , a sequence of 24 original frames, as shown in  FIG. 2 , is reconstructed as demonstrated by the step-by-step diagram of  FIG. 4 . In the diagram of  FIG. 4 , at each step, a decode is begun on a frame indicated in italicized type with the decode completed at the start of a next frame decode, a frame indicated in boldfaced type is displayed, and a frame indicated with strikethrough type is released from memory. Frame numbers indicated in normal type are held in memory. 
     In the example of  FIG. 4 , the process of reverse playback begins with a first frame I 24 , as the one immediately preceding a currently displayed frame. The I-frame preceding I 24  is determined to be I 12 , which is shown as being decoded in step 1). With I 12  decoded in step 2), it is able to provide the reference data for the frame P 15 , which starts its decode. With P 15  decoded in step 3), it is able to provide the reference data for the frame P 18 , which starts its decode. In step 4), P 18  is decoded and provides the reference data necessary for starting the decode of frame P 21 . In step 5), the data needed for frame I 24  is present and its decode is started. Continuing with step 6), the I 24  frame is displayed, and its data, together with the data from P 21 , provides the needed reference data to begin the decode of frame B 23 . Thus, in step 7), the decoded B 23  data is displayed and the decode of B 22  begins. With B 22  decoded and displayed in step 8), the memory for B 23  and I 24  data is released, since neither will be used in any further decode. Further, since the next preceding frame P 21  is already decoded, a next preceding I-frame,  10 , is located and decoded in step 8). The data decoded for P 21  is displayed in step 9), while the decode for the B 20  frame is begun and the memory for B 22  is released. In step 10), B 20  is displayed while the decode of B 19  is begun. In step 11), B 19  is displayed, the memory for B 20  and P 21  is released, and the decode of P 3  is begun. In step 12), P 18  is displayed, the decode of B 17  is begun, and the memory for B 19  is released. With B 17  decoded, it is displayed in step 13), while the decode of B 16  begins. The decoded B 16  is displayed in step 14), allowing the release of memory for its reference P 18 . Also in step 14), the memory for B 17  is released and the decode of P 6  is begun. In step 15), P 15  is displayed, the decode for B 14  is begun, and the memory for B 16  is released. Once decoded, B 14  is displayed in step 16), and the decode for B 13  is begun. B 13  is then displayed in step 17), the memory for B 14  and P 15  is released, and the decode of P 9  occurs. In step 18), I 12  is finally displayed, the memory for B 13  is released, and the decode of B 11  begins. 
     The process demonstrated by  FIG. 4  is cyclic. Thus, continuing with steps 19-30 would repeat steps 7-18 except on differently numbered frames, where the indices for the frame number are decremented by 12 every cycle. Further, in each step of the diagram, only 7 frames of data is stored in memory in one embodiment. For example, in step 1), only one buffer is allocated to store I 12 . In step 4), four buffers are allocated to store I 12 , P 15 , P 18 , and P 21 . In step 10), seven buffers are allocated to store  10 , I 12 , P 15 , P 18 , B 19 , B 20 , and P 21 . Thus, the reconstruction for backwards playback need not use more than seven frame buffers during any one step in one embodiment. Of course, more buffers could be used in other embodiments. The decode process of the present invention may operate on sets of 12 frames (e.g., in accordance with the DVD standard which prescribes that I-frames occur no less frequently than every 12 frames). At a high level, the player appears to decode the sets in reverse order. At a low level, the player decodes each frame within a set in forwards order, which computationally is well within the existing capacity of a DVD player system, as represented in  FIG. 1 . 
     Single Frame Stepping Backwards 
     In a further aspect, the reverse playback is modified to allow the DVD player system to display one frame at a time in reverse order. The implementation occurs as described above for smooth rewind, with the following differences, as shown in  FIG. 5 . The DVD player system waits for a signal from the user to step the frame backward (step  120 ) before starting the reconstruction of a preceding frame (step  121 ). The data is stored utilizing one of at least seven frame buffers (step  122 ). Once reconstructed, the frame is displayed (step  123 ) and the process returns to step  120  to await another signal indicating selection for single frame reverse. 
     Smooth Search Transitions 
     In yet another embodiment, the present invention provides for smooth search transitions in a DVD player system (e.g., transitions between one playback rate and another with reduced jerk). The limited frame rates of some displays, such as televisions, force DVD players to make the transition between one display rate and another abruptly. However, the frame rates of PC displays, for example, are flexible and thus, a PC-based DVD player system can make the transition between display rates smoothly. Thus, the aspect of smooth search transitions preferably is utilized in a DVD player system that provides data to displays that do not have limited frame rates. 
     In order to achieve smooth transition between display rates, the present invention linearly interpolates between one rate and another over a brief transition interval. Thus, with a given starting rate (r 0 ), a new rate (r 1 ), the time the player is aware of the eminent transition (t 0 ), and the time of the scheduled transition (t 1 ), the transition interval is defined to be the time between t 0  and t 1 +(t 1 −t 0 ), which provides a sufficient interval to maintain the overall average rate and in turn keeps audio and video in synchronization in one embodiment. A parametric equation R(t) is defined for the rate over the interval where the parametric u varies from 0 to 1, where 0 represents t 0  and 1 represents t 1 +(t 1 −t 0 ).
 
 U =(now− t 0)/( t 1 −t 0)
 
 R ( t )= r 0 +u ( r 1 −r 0)
 
       FIG. 6  illustrates a block flow diagram for performing smooth search transitions. As shown in  FIG. 6 , an instantaneous rate is calculated for every frame using the frame&#39;s original timestamp as input (e.g., the “now” variable above) (step  124 ). The resulting rate is then used to calculate an adjusted timestamp for the frame (step  126 ). The frame is then displayed according to the adjusted timestamp (step  128 ). Thus, when the frames are provided with the adjusted timestamps, video playback appears as a smooth increase or decrease in playback speed (e.g., without the “jerk” associated with conventional systems) when transitioning between speeds (e.g., 0.5×, 1×, 2×, 4×, 8×, etc.). 
     In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is, and is intended by the applicant to be, the invention is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Hence, no limitation, element, property, feature, advantage, or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.