Abstract:
Systems and methods for previewing edited video. In general, in one implementation, a method includes generating a video sequence from a plurality of video segments, identifying an inability to output at least one video segment in the video sequence in substantially real time; and adjusting an output level associated with the at least one video segment to enable the at least one video segment to be output in substantially real time. The output level may include a video quality or a frame rate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. application Ser. No. 11/107,397, filed Apr. 15, 2005 entitled “Dynamic Real-Time Playback, which is hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The following disclosure generally relates to systems and methods for previewing edited video. 
         [0003]    A video editing application allows a user to generate an output video sequence from various video sources. A video camera can capture and encode video information in various video formats (e.g., MPEG, AVI, or DV) that can be used as video sources. A user can make edits to create a video sequence composed of desired portions of the video sources and to add effects thereto. 
         [0004]    Some video editing applications include features allowing users to preview an output video sequence. A user may want to experiment with different types of effects, or place effects at different positions along a timeline. A user may also want to check actual colors on an NTSC display device. By using the preview feature, a temporary output video sequence can be played back immediately after generating the video sequence. But, the processing required for rendering multiple video formats and/or complex edits in substantially real time can lead to playback with unintentionally dropped frames or a lowered video quality. 
         [0005]    Another feature that is available in some video editing applications allows rendering an output video sequence for persistent storage. In rendering, the native formats are transformed to a single output format. The rendered video can be persistently stored as a file. However, persistent rendering can require significantly more time than previewing such that repeated re-rendering is impractical during video editing. 
       SUMMARY 
       [0006]    This disclosure generally describes systems and methods for previewing edited video. A proposed system can preview a video sequence in substantially real time without time-consuming and processor-intensive rendering. The proposed system can provide user control to video playback settings and take into account capabilities associated with a particular playback device to indicate to a user whether video playback at a desired level can be guaranteed or predicted to be in substantially real time. Alternatively, the proposed system can automatically adjust portions of a video sequence to at a highest possible output level (e.g., video quality or frame rate) for preview with a predictable performance. 
         [0007]    In one aspect, a method is provided. The method comprises generating a video sequence from a plurality of video segments; identifying an inability to output at least one video segment in the video sequence in substantially real time; and adjusting an output level associated with the at least one video segment to enable the at least one video segment to be output in substantially real time. 
         [0008]    Particular implementations can include one or more of the following features. The method can further comprise preserving an output level associated with video segments in the video sequence that are able to be output in substantially real time. The method can further comprise selecting a video quality; identifying an inability to output a particular video segment in substantially real time at the selected video quality; and adjusting a level of video quality associated with the particular video segment, the adjustment being to a highest available level that allows output of the particular video segment in substantially real time. The method can further comprise selecting a frame rate; identifying an inability to output a particular video segment in substantially real time at the selected frame rate; and adjusting a level of frame rate associated with the particular video segment, the adjustment being to a highest available level that allows output of the particular video segment in substantially real time. 
         [0009]    The method can further comprise outputting the video sequence in substantially real time including dynamically allocating buffer sizes associated with outputting the video sequence in accordance with a frame resolution of each video segment in the video sequence. The output level can comprise at least one level selected from the group consisting of a video quality and a frame rate. The method can further comprise displaying a first indicator in a graphical display of the video segments in the video sequence, the first indicator graphically indicating video segments that are able to be output in substantially real time at a full output level; displaying a second indicator in the graphical display of the video segments in the video sequence, the second indicator graphically indicating video segments that are able to be output in substantially real time at a reduced output level; and displaying a third indicator in the graphical display of the video segments in the video sequence, the third indicator graphically indicating an inability to be output the video segments in substantially real time. 
         [0010]    The method can further comprise calculating a cost associated with outputting each of the video segments in real time, the cost being in terms of system resources, wherein identifying the inability to output is based on the cost. The method can further comprise identifying video playback capabilities associated with system resources that are operable to output the video sequence, wherein identifying the inability to output is based on the cost. The system resources can comprise one or more resources selected from a group consisting of a processor, a memory, a graphics processor, a cache, and a bus. Generating can comprise editing a subset of the plurality of video segments to add an effect. 
         [0011]    The method can further comprise after adjusting the output level, outputting the video sequence in substantially real time. The method can further comprise rendering the output video responsive to the inability to output the at least one video segment in substantially real time. Output in substantially real time can refer to output having consistency in the output level. Output in substantially real time can be within a predetermined level of accuracy of strict real time. 
         [0012]    In general, in another aspect, a method is provided. The method comprises generating a video sequence from a plurality of video segments; identifying video playback capabilities associated with system resources that are operable to output the video sequence; calculating a cost associated with outputting one or more of the video segments in the video sequence in real time, the calculated cost representing a utilization level of the system resources; identifying an inability to output at least one video segment in substantially real time based on the cost; adjusting an output level associated with the at least one video segment; and outputting the video sequence in substantially real time using the adjusted output level. 
         [0013]    Particular implementations can include one or more of the following features. The output level can comprise at least one level selected from the group consisting of a quality level and a frame rate. 
         [0014]    In general, in another aspect, a method is provided. The method comprises generating a video sequence from a plurality of video segments; selecting an output level; identifying an inability to output at least one video segment in the video sequence in substantially real time; displaying a first indicator in a graphical display of the video segments in the video sequence, the first indicator graphically indicating video segments that are able to be output in substantially real time at a full output level; displaying a second indicator in the graphical display of the video segments in the video sequence, the second indicator graphically indicating video segments that are able to be output in substantially real time at a reduced output level; and displaying a third indicator in the graphical display of the video segments in the video sequence, the third indicator graphically indicating an inability to be output the video segments in substantially real time. 
         [0015]    In general, in another aspect, a method is provided. The method comprises generating a video sequence from a plurality of video segments; reducing a first frame resolution associated with the at least one video segment to a second frame resolution to enable the at least one video segment to be output in substantially real time; receiving the first and second frame resolutions in association with corresponding video segments; and dynamically allocating buffer sizes associated with processing the video sequence for output, the buffer sizes configured to have a first capacity when processing a video segment at the first frame resolution and the buffer sizes configured to have a second capacity when processing a video segment at the second frame resolution. 
         [0016]    In general, in another aspect, a computer program product tangibly stored on a computer-readable medium is provided. The computer program product comprises instructions operable to cause a computer system to perform a method, including generating a video sequence from a plurality of video segments; identifying an inability to output at least one video segment in the video sequence in substantially real time; and adjusting an output level associated with the at least one video segment to enable the at least one video segment to be output in substantially real time. 
         [0017]    In general, in another aspect, a system is provided. The system comprises an editing timeline configurable configured to generate a video sequence from a plurality of video segments; and a preview block, in communication with the editing timeline, the preview block configurable to identify an inability to output at least one video segment in the video sequence in substantially real time, the preview block adjusting an output level associated with the at least one video segment to enable the at least one video segment to be output in substantially real time. 
         [0018]    Particular implementations can include one or more of the following features. The system can comprise a real time engine, in communication with the editing timeline and the preview block, the real time engine configured to output the video sequence in substantially real time including dynamically allocating buffer sizes associated with outputting the video sequence in accordance with a frame resolution of each video segment in the video sequence. The output level can comprise at least one level selected from the group consisting of a video quality and a frame rate. The editing timeline can display a first indicator in a graphical display of the video segments in the video sequence, the first indicator graphically indicating video segments that are able to be output in substantially real time at a full output level, the editing timeline can display a second indicator in the graphical display of the video segments in the video sequence, the second indicator graphically indicating video segments that are able to be output in substantially real time at a reduced output level, and the editing timeline can display a third indicator in the graphical display of the video segments in the video sequence, the third indicator graphically indicating an inability to be output the video segments in substantially real time. 
         [0019]    The preview block can comprise a cost block to calculate a cost associated with outputting each of the video segments in real time, the cost being in terms of system resources, wherein the preview block identifies the inability to output is based on the cost. The preview block can comprise a resource block to identify video playback capabilities associated with system resources that are operable to output the video sequence, wherein the preview block identifies the inability to output is based on the cost. The system resources can comprise one or more resources selected from a group consisting of a processor, a memory, a graphics processor, a cache, and a bus. 
         [0020]    The system can comprise a rendering engine, in communication with the preview block, the rendering engine configured to render the output video sequence responsive to the inability of the preview block to output the at least one video segment in substantially real time. Output in substantially real time can refer to output having consistency in the output level. Output in substantially real time can be within a predetermined level of accuracy of strict real time. 
         [0021]    Details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages may be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0022]      FIG. 1  is a block diagram illustrating a system for previewing edited video. 
           [0023]      FIG. 2  is a schematic diagram illustrating an editing timeline in the system of  FIG. 1 . 
           [0024]      FIG. 3  is a block diagram illustrating a preview block in the system of  FIG. 1 . 
           [0025]      FIGS. 4A-B  are schematic diagrams illustrating first and second user interfaces associated with the preview block of  FIG. 3 . 
           [0026]      FIG. 5  is a flow diagram illustrating a method for previewing edited video. 
           [0027]      FIG. 6  is a flow diagram illustrating a method for identifying video output capabilities. 
           [0028]      FIG. 7  is a flow diagram illustrating a method for calculating a cost for video playback of a video sequence. 
           [0029]      FIG. 8  is a flow diagram illustrating a method for determining which of the video segments are able/unable to be previewed in substantially real time. 
           [0030]      FIG. 9  is s flow diagram illustrating a method for adjusting an output level associated with the video segments. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]      FIG. 1  is a block diagram illustrating a system  100  that can be used to playback a video sequence. The system  100  can be, for example, a personal computer, a PDA, a cellular telephone, and the like. The system  100  includes a memory  102 , a processor  104 , a graphics processor  106 , a storage  108 , and a display device  110 . The memory  102  further includes a video editor  152 , a rendering allocation  154  and an operating system  156 . Line  199  can be a bus or other communication medium that facilitates communication between the components. 
         [0032]    The memory  102  can be a volatile storage resource, for example, a RAM module. The memory  102  can store data and instructions associated with executing applications. The video editor  152  can be, for example, Final Cut Pro by Apple Computers of Cupertino, Calif., a nonlinear video editor, or other software that enables editing of video sources. The video editor  152  in the memory  102  further includes an editing timeline  162 , a preview block  164  and a real time engine  166 . The editing timeline  162 , as described more fully below in association with  FIG. 2 , allows a user to edit various video sources into video segments and to organize the video segments into a video sequence. Edits can include, for example, cross-fades, dissolves, picture-in-picture, overlays, splices, and the like. The preview block  164 , as described more fully below in association with  FIG. 3 , adjusts (e.g., automatically or dynamically) an output level of the video segments in the video sequence such that the video sequence can be output in substantially real time. In some implementations, substantially real time refers to producing frames such that they can be displayed at a consistent video quality (e.g., high, medium, or low) and/or frame rate (e.g., 30 frames/second or 15 frames/second). In other implementations, substantially real time has a predetermined tolerance with respect to strict real time (e.g., 3%). In one implementation, a user viewing the output video sequence will not perceive any gaps, delays, skips, or other time induced artifacts during display. 
         [0033]    The real time engine  166  can include, for example, a media handler (not shown). The real time engine  166  provides a preview of the output video sequence by rendering the output video sequence in substantially real time. To do so, the real time engine  166  uses a pipeline architecture to schedule data retrieval, render frames, and send rendered frames to the display device  110 . To render frames, the real time engine  166  decodes frames, applies effects, and composites frames. The real time engine  166  can implement several decoders depending on how many different native formats make up the output video sequence. The real time engine  166  can allocate buffers in the rendering allocation  154  dynamically, based on a desired quality of a particular video segment in the video sequence. For example, a decode buffer, an effects buffer, and a composite buffer can be allocated a different capacity on-the-fly for each video segment. In some implementations, a rendering engine (not shown) is provided to generate the output video sequence when real time is not necessary (e.g., when creating a persistent file). The rendering engine can typically produce video at a desired quality and frame rate because it can take several passes and as much time as needed in generating the output video sequence. 
         [0034]    The rendering allocation  154  can be, for example, a portion of the memory  102  which can be further subdivided into the above-described buffers. A size of the rendering allocation  154  can be set by a request from the video editor  152  to the operating system  156 . In some implementations, the rendering allocation  154  is dedicated to storing information from the video editor  152  related to previewing a video sequence. For example, the rendering allocation  154  can store a batch of video frames to be rendered, video frames being rendered, and rendered video frames to be displayed. 
         [0035]    The operating system  156  can be, for example, OS X by Apple Computers of Cupertino, Calif., a Windows operating system, a mobile operating system, control software, and the like. In some implementations, the operating system  156  interfaces between the preview block  164  and system resources used for video playback. The operating system  156  can manage drivers for system resources that are initialized at boot up. In addition, the operating system  156  can spawn windows and initialize the video editor  152 . By being in communication with both sides, the operating system  156  can send an accounting of system resources to the preview block  164  as a static measurement, or at the time of video playback. 
         [0036]    The processor  104  can be a microprocessor such as an ARM processor, a Pentium processor, an Athlon processor, an ASIC, an FPD (Field Programmable Device), a microcontroller, and the like. The processor  104  can include local resources (not shown), for example, a level-1 cache, a level-2 cache, a floating point unit, an internal bus, and the like. In some implementations, a unified value is reported for the processor  104 , and in other implementations, individual values are reported for the local resources of the processor  104 . The processor  104  can execute instructions and manipulate data necessary for video playback using the local resources. In other implementations, such as in a personal computer, the processor  104  can allocate its resources for tasks that are unrelated to video playback. 
         [0037]    The graphic processor  106  can be a microprocessor such as the processor  104 , a GeForce processor, a Radeon processor, an assist processor, and the like. The graphics processor  106  can include local resources such as those described in association with processor  104 . The graphics processor  106  can be dedicated to graphics processing such as executing instructions and manipulating data necessary for video playback using the local resources. 
         [0038]    The storage  108  can be a nonvolatile memory, for example, a hard disk, a flash drive, a video tape, and the like. The storage  108  can persistently store video data used as source video for the video editor  152 . The video data can be stored in various video formats such as MPEG, AVI, DV, and the like. The storage  108  can send the video data to the rendering allocation  154  during video playback. The storage  108  can also record previews of the output video sequence. 
         [0039]    The display device  110  can be, for example, a monitor. The display device  110  provides visual representations of the playback video to a user. For example, the display device  110  can be an LCD monitor. 
         [0040]      FIG. 2  is a schematic diagram illustrating an example of the editing timeline  162 . The editing timeline  162  includes a reel A  202  and a reel B  204  which together contain video segments  203 , 205 , 207 . The editing timeline  162  also includes an effects timeline  206  which contains various effects  209 , 211 , 213 . During previewing, composite frames of video segments  203 , 205 , 207  and effects  209 , 211 , 213  are generated. During compositing, several sources can be evenly mixed, or sources can be layered on top of each other, to combine the several sources into a single frame. At different points in time (e.g., 0, 1, 2, 3, 4, 5 or 6), there are transitions between which sources are combined. For example, during time interval 0-1, reel A  202  and effects  209  are combined; during time interval 1-2, reels A and B  202 , 204  are combined; during time interval 2-3, reel B  204  is an exclusive source; and during time interval 3-4, reels A and B  202 , 204  and effects  206  are combined. 
         [0041]    In addition, the editing timeline  162  includes a real time timeline  208  which contains indications  240 - 252  of whether corresponding portions of the video sequence can be played back in substantially real time given the available system resources. During time interval 0-1, the indication  240  is grey. The grey indication  240  can indicate that rendering the combination of video segments  203 , 209  is within the video output capabilities of associated system resources. During time interval 1-2, the indication  242  is green. The green indication  242  can indicate that rendering the combination of the video segments  203 , 207  has to be done at a lower quality or frame rate in order to provide substantially real time video playback over this portion. In another implementation, the green indication  242  is responsive to a user selection that forces playback at less than full quality. Frames in these portions of the video segments  203 , 207  may be poorly compressed responsive to, for example, fast action scenes or a high density of colors on the frames. During time interval 2-3, the indication  244  is grey. The grey indication  244  can indicate that the video segment  207  can be output at a full output level without the additional requirements of rendering the video segment  203  as is the case at time 2. Finally, during time interval 3-4, the indication  246  is red. The red indication  246  can indicate that rendering the combination of three different video sources is beyond available system resources at any rate. In some implementations, this portion of the video sequence is pre-rendered in a background process and, upon completion, the indication  246  can switch to grey. 
         [0042]      FIG. 3  is a block diagram illustrating one implementation of the preview block  164 . The preview block  164  includes a resource block  302 , a cost block  304  and an adjustment block  306 . At a high-level, the adjustment block  306  uses information provided by the resource block  302  and the cost block  304  to determine if any adjustments are necessary for playing back video in substantially real time. 
         [0043]    The resource block  302  can receive resource data from the operating system  156  ( FIG. 1 ). Also, the resource block  302  can send resource data to the cost block  304 . The resource block  302  can detect availability and capacity of system resources responsive to, for example, initialization of the video editor  152 , a particular resource, or the system  100 . In some implementations, the resource block  302  sends queries and identifies video playback capabilities of the system  100  based on resource data received in response to the queries. The source block  302  can send the resource data as raw data, for example, a processor clock rate, a processor bus rate, a buffer size, a system bus rate, and the like. In some implementations, the source block  302  can send the resource data as unified measurement of video playback capability. 
         [0044]    The cost block  304  can receive video sequence data from the editing timeline  162  ( FIG. 1 ). Also, the cost block  304  can send cost data to the adjustment block  306 . The cost block  304  can include a list of costs associated with various video editing operations such as a categorization of editing operations as high cost, medium cost, and low cost. The cost block  304  uses the video sequence data received to identify editing operations for particular portions of video segment in the video sequence and correlate the editing operations to the list of costs. The cost block  304  can determine costs on a per segment basis with respect to editing operations in isolation, or with respect to video playback capabilities of a particular system  100  (e.g., cost as a percentage of available system resources). 
         [0045]    The adjustment block  306  can receive cost data and user configurations. Also, the adjustment block can send visual indications for display to a user. The adjustment block  306  can be configured through a user interface for the type of desired video playback (e.g., dynamic, high or low quality, high or low frame rate), as described below in association with  FIGS. 4A-B . The adjustment block  306  can identify which of the video segments are able/unable to be played back in substantially real time according to the configurations. In some implementations, a subset of frames that are unable to be played back can cause an entire video segment or other portion thereof to be designated as unable to be played back. The adjustment block  306  can visually indicate whether each video segment can be played back as desired, for example, with a grey, a green or a red marker. In some implementations, the adjustment block  306  changes an output level associated with a particular video segment so that it can be played back in substantially real time. The output level can relate to a video quality setting, a frame rate setting, or other settings that impact the bit rate of an output signal. 
         [0046]      FIG. 4A  is schematic diagram illustrating one implementation of a first user interface  400  associated with the preview block  164  ( FIGS. 1 and 3 ). The first user interface  400  includes a window  402  that can be accessed while using a timeline  408 . The window  402  has several configurations that can be set by a user. Specifically, a playback video quality setting  404  can be changed between, in the implementation shown, dynamic, high, medium, and low qualities. A playback frame rate setting  406  can be changed between, in the implementation shown, dynamic, full, half, and quarter frame rates. The playback video quality and frame rate settings  404 , 406  allow high level settings of video playback for low level characteristics with a mouse or a minimal amount of keystrokes. For example, a user can select a dynamic quality to automatically guarantee a highest quality of preview on a per video segment basis. This can be used to, for example, view colors or details that would be output in a persistent rendering. In another example, a user can select a dynamic frame rate to automatically guarantee a highest frame rate of preview on a per video segment basis. This can be used, for example, to view a flow of transitions that would be output in a persistent rendering. 
         [0047]      FIG. 4B  is a schematic diagram illustrating one implementation of a second user interface  450  associated with the preview block  164 . The second user interface  450  includes a dialog box  452  with a playback control tab selected. The second user interface  450  can be accessed from, for example, a drop down menu. Similar to  FIG. 4A , the second user interface  450  includes a video quality setting  454  and a frame rate setting  456 . 
         [0048]      FIG. 5  is a flow diagram illustrating a method  500  for playing back a video sequence. In general, video segments in a video sequence are adjusted to an output level that allows the video sequence to be previewed in substantially real time. 
         [0049]    A video sequence is generated  510  from video segments (e.g., by the editing timeline  162 ). To do so, a user can drag and drop selected video sources into a timeline and use a trimming operation to isolate video segments from the video sources. For example, the video segments can include a roll A of wide shots and a roll B of close ups. In the example, a user can select a video segment from roll A for an opening shot, switch to a video segment from roll B to draw attention to a subject, and then switch back to a different video segment from roll A for a closing shot. A user can also add effects to or across video segments such a fade, dissolve, color correction, and the like. 
         [0050]    Video playback capabilities are identified  520  for system resources that will output the video sequence (e.g., by the resource block  302 ), as shown in detail in the flow diagram of  FIG. 6 . The system resources are initialized  610 . At events such as power on, boot up, and the like, the system resources become available for use in video playback. A list of specific hardware and/or software can be maintained that, in some implementations, also includes a list of local resources on the hardware and/or software. 
         [0051]    The system resources available for video playback are queried  620  (e.g., via the operating system  156 ). In some implementations, the list of system resources can be queried for specific capabilities. For example, a data rate or bus rate of a processor can be determined or a capacity of a memory is determined. In some implementations, the system resources are queried at any time, such as at initialization. In other implementations or situations, the system resources are queried when video playback is desired in order to get a current state of available system resources. 
         [0052]    A unified measurement for video playback capability is determined  630 . The system resources can include, for example, the rendering allocation  154  in the memory  102 , the processor  104 , the graphics processor  106 , the storage  108 , and the display device  110 . In some implementations, points are accumulated for each of the system resources, and for specific capabilities of the system resources. For example, a graphics processor is an optional system resource that can significantly increase the video playback capability of a general system such as personal computer. In the example, points are assigned for the presence of the graphics processor and additionally for features such as DDR, L1 cache size, and the like. The sum is the unified measurement that provides a single measure for playback capability of the system resources. 
         [0053]    As shown in  FIG. 5 , the cost is that is associated with outputting each of the video segments in substantially real time is calculated  530  (e.g., by the cost block  304 ), as shown in detail in the flow diagram of  FIG. 7 . A list of costs associated with video editing operations is received  710 . For example, the video editing operations can be separated into categories of high cost, medium cost and low cost. High cost operations can include blur and high definition effects, middle cost operations can include motion and pan/zoom effects, and low cost operations can include color correction, cross dissolves, wipes, and text. In another example, video editing operations can have more precise costs assigned. 
         [0054]    Video sequence data is received  720  (e.g., from the editing timeline  162 ). The video sequence data identifies editing operations for particular video segments of the video sequence. The video sequence data can separate the video sequence into video segments that are distinguished by video source or applied effects. Video sources can have native differences such as video format, frame rate, quality and the like that require a different amount of playback capability. The editing operations are correlated  730  to the list of costs for each of the video segments. 
         [0055]    As shown in  FIG. 5 , the video segments that are able/unable to be output in substantially real time are determined  540  (e.g., the adjustment block  306 ), as shown in detail in a flow diagram of  FIG. 8 . A desired output level can be received  810 . In some implementations, a user can select a playback video quality and a playback video frame rate. When the quality is set to dynamic, each segment is played back at the highest possible quality. When a specific quality such as high is selected, each video segment is played back at the selected quality. If system resources are not able to maintain substantially real time video playback a the desired quality, the frame rate is dropped (e.g., a frame rate can drop from 1/30 s to 1/15 s in order to maintain a high quality). When the frame rate is set to dynamic, each segment is played back at the highest possible frame rate. When a specific frame rate such as full is selected (e.g., 1/30 s), each video segment is played back at the full rate. If system resources are not able to maintain substantially real time video playback at the desired frame rate, the quality is dropped. 
         [0056]    The cost of each of the video segments is compared  820  to the video playback capabilities. The video segments that have a higher cost than available system resources will not be able to be played back in substantially real time. A visual indication of whether each of the video segments can be played back in substantially real time at the desired output level is displayed  830 . For example, video segments marked with grey are guaranteed to be played back in substantially real time at a desired (or full) output level, video segments marked with grey are guaranteed to be played back at a lower than desired output level, and video segments marked with red cannot be played back in real time. In one implementation, background processes begin rendering grey and red marked video segments to make them playable in real time. 
         [0057]    In  FIG. 5 , an output level is adjusted  550  for video segments that are unable to be output in substantially real time (e.g., by the adjustment block  306 ), as shown in the flow diagram of  FIG. 9 . For video segments that cannot be played back in substantially real time  910 , a highest output level is determined  920 . The output level associated with video segments that are unable to be played back in substantially real time are adjusted  930  to the determined highest output level. Each of the video segments  940  is adjusted separately. 
         [0058]    The video sequence is output  560  in substantially real time (e.g., by real time engine  166 ). In some implementations, the output is a preview of the video sequence that is played back using the native video source where no effects are applied. Effects are rendered in substantially real time at the determined output level. At a later point, such as when editing is complete, or when an output file is needed, the output video sequence can be rendered. 
         [0059]    Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in special purpose logic circuitry. 
         [0060]    To provide for interaction with a user, the invention can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. 
         [0061]    The invention can be implemented in, e.g., a computing system, a handheld device, a telephone, a consumer appliance, or any other processor-based device. A computing system implementation can include a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the invention, or any combination of such back-end, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (“LAN”) and a wide area network (“WAN”), e.g., the Internet. 
         [0062]    The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. 
         [0063]    A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. In one implementation, for example, to measure a distribution of residues in a set of numbers (e.g., a set of numbers produced by a pseudorandom number generator). Accordingly, other implementations are within the scope of the following claims.