JP2004343512A - Video reproducing method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for realizing searching operations with high visibility for maximizing the decoding processing capability within a range wherein a video can smoothly be reproduced in high speed reproduction of a video signal subjected to inter-frame prediction coding. <P>SOLUTION: In the case of applying high speed reproduction to an MPEG stream 100 comprising an in-frame coded frame 101 and an inter-frame prediction coded frame 102, the stream is decoded while decreasing a decoding area 111 in a vertical direction on the basis of a value 110 according to the maximum value of a vector searching range in the vertical direction and a search speed / decoding processing capability, frame data 103 for updating the display are selected from slice data included in the decoding area 111 and displayed to attain high speed reproduction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a video reproducing method for reading and reproducing an inter-frame predictive-coded video from a recording medium such as an optical disk, and can display a search video with higher visibility when decoding at a higher speed than in real time is possible. It relates to a video playback method.
[0002]
[Prior art]
Devices using digital recording and reproduction of video are increasing irrespective of whether they are for home use or business use. Realizing long-time recording and high image quality with a limited medium capacity is a contradictory element, but a series of MPEG standards (Moving Pictures coding Experts Group: ISO / IEC 11172-2) based on inter-frame coding. , ISO / IEC13818-2 and ISO / IEC14496-2) have high cost performance in terms of compression ratio and image quality, and have been adopted in many applications such as digital TV broadcasting, DVD-Video, and mobile phones.
[0003]
In video coding based on MPEG, each frame is coded with a configuration as shown in FIG. The coding type includes three types of an intra-coded frame (hereinafter, referred to as an I frame), an inter-frame coded frame (hereinafter, referred to as a P frame), and a frame interpolation coded frame (hereinafter, referred to as a B frame). There are types. An I frame is a frame that can be decoded using only the data of the frame. The P frame is a frame that can be decoded using only the data of the I or P frame decoded before the frame and the data of the frame, and the B frame is the two I or P frames that are temporally adjacent to each other. This is a frame that can be decoded using the data of the frame and the data of the frame. Since the B frame refers to the subsequent frame in the display order, the B frame is coded by changing the order as shown in FIG. In many cases, the encoded data is sequentially output as a bit stream (hereinafter, referred to as a stream) as a sequence of GOPs (Group Of Pictures) starting from an I frame. When only the I frame and the P frame are coded, the result is as shown in FIG. 12, and the coding order and the display order are the same. Decoding of an MPEG stream is performed in the order of encoding after reading frames from the stream in the order of encoding. Video output is performed in the order of display.
[0004]
Special reproduction, particularly high-speed reproduction, of an MPEG stream involves great difficulty. For example, consider a case where a stream as shown in FIG. 13 is read and quadruple speed reproduction is performed. Assuming that the current frame is the I frame of frame 2 and considering only the frame index in the range of 0 to 14, the reproduction speed of four frames of frames 2, 6, 10, and 14 is quadruple speed. However, as shown in the figure, decoding of each frame requires 1, 4, 5, and 5 decoding times including the prediction reference frame. This means that in one frame time (33 msec for NTSC and 40 msec for PAL), smooth reproduction cannot be performed unless (1 + 4 + 5 + 5) /4=3.75 frames are decoded on average.
[0005]
On the other hand, a general-purpose MPEG decoder such as an LSI generally operates in real time in conjunction with a clock for normal reproduction (1 × speed reproduction), and has a configuration in which one frame is decoded in one frame time. For this reason, the fast-forward playback function of DVD-Video and the like merely displays and updates an I frame like frame advance. From the above, it can be seen that it is difficult to smoothly reproduce a video encoded by MPEG at high speed.
[0006]
Applications for editing MPEG-encoded video have become widespread not only for business such as broadcasting and content production, but also for home use. When performing cut editing, which is the most common in video editing work, a search operation for performing playback at several times the playback speed is performed in order to quickly search for a desired scene or a target person or object. As a display method at the time of search, it is a general method to display one frame for every several frames according to the double speed. However, an object that appears only in the skipped frame is not displayed at the time of the search, so that the visibility of such an object is not sufficient. Further, as described above, since high-speed reproduction of an MPEG stream requires high decoding processing capability, when the decoding processing capability is insufficient, a frame cannot be updated within one frame time and a smooth search operation can be performed. Absent. As described above, there are many problems in applying the search operation of the MPEG stream to the application.
[0007]
Many patents have been filed as a conventional technique for performing a search operation on a video encoded by MPEG. First, there is Patent Document 1 as a typical method for improving visibility. As shown in FIG. 14, in the case of n-times speed (n is an integer of 2 or more), different portions of n-divided frames are collected and displayed as one frame. This increases the probability that an object that exists only in a specific frame can be displayed. However, it is assumed that decoding processing is performed at n times speed in the case of n times speed, that is, all necessary frames are decoded. For example, even at 4 × speed playback, decoding processing must be performed at 4 × speed, which is not particularly suitable for playback of a stream having a large decoding processing load, such as high resolution video of high quality.
[0008]
As described in Patent Document 1, an intra slice in Non-Patent Document 1 of the MPEG2 standard is a known technique for displaying different portions of an n-divided frame and reducing decoding processing. A slice is a unit in which a plurality of 16 × 16 pixel macroblocks are gathered in the horizontal direction, and generally only one slice is arranged at the same vertical position in one frame. The intra slice is a mode in which all macro blocks in the slice are encoded as intra macro blocks based on a flag defined in the syntax in the slice. If the intra slices are arranged as shown in FIG. 14, information of n frames can be displayed as one frame only by decoding processing for one frame. As an application example of the intra slice, there is a technique in which a code length is added to overhead data as in Patent Document 2, for example. However, special reproduction using intra-slices cannot deal with flexible changes in reproduction speed because the arrangement of slices that can be specially reproduced is determined at the time of encoding. There is a problem in that the image quality is deteriorated due to the poor intra coding.
[0009]
[Patent Document 1]
JP 2001-352524 A (FIG. 6)
[Patent Document 2]
Japanese Patent No. 3231833 (Claim 1)
[Non-patent document 1]
ISO / IEC13818-2: Information Technology-Generic coding of moving pictures and associated audio information: Video (6.2.4 Slice)
[0010]
[Problems to be solved by the invention]
When a search operation is performed on a medium on which an interframe predictive encoded video typified by MPEG is recorded, a smooth operation is performed in consideration of the decoding processing capability while increasing the visibility of an object when searching for a scene. No method of reproducing the video has been proposed.
[0011]
SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems. In high-speed reproduction of an interframe predictive-encoded video signal, visibility is maximized by utilizing decoding processing capability within a range in which video can be smoothly reproduced. It is an object of the present invention to obtain a method for achieving a high search operation.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a video reproducing method according to the present invention provides a method for reproducing a video signal composed of an intra-coded frame and an inter-frame predicted coded frame at a high speed and a maximum value of a vector search range in a vertical direction. High-speed playback is performed by decoding while reducing the decoding area in the vertical direction according to the value determined by the speed and decoding processing capacity, and selecting and displaying slice data for updating the display from the slice data included in the decoding area.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0014]
(Embodiment 1)
FIG. 2 is a block diagram for realizing the video reproducing method according to the present invention. In FIG. 2, reference numeral 420 denotes a recording medium on which a video is recorded, 440 denotes a reproduction operation input unit for a user to perform a reproduction operation, 450 denotes a video reproduction unit for performing video reproduction according to the present invention, and 432 denotes a display device. is there.
[0015]
In FIG. 2, the user operates the reproduction operation input unit 440 to perform a reproduction operation. By the reproduction operation, the start time code Ts and the reproduction speed Vp are transmitted to the video reproduction means 450. There are various methods for realizing the reproduction input means. Any method can be used as long as the playback speed Vp can be changed and transmitted to the video playback means, such as buttons for playback / stop / fast-forward and a jog dial used for an editing / playback machine. The video reproducing unit 450 reads the video recorded on the recording medium 420 and reproduces the video at the reproduction speed Vp from the start time code Ts. The reproduced video is displayed on the display device 432. As the recording medium 420, a device such as a tape, an optical disk, a magnetic disk, and a memory can be used.
[0016]
FIG. 3 shows a flowchart of a reproducing process in the video reproducing method of the present invention. In a reproduction process 260 for reproducing a video, a process 261 for moving to a start time code Ts is performed. By this process, the time code Ts is searched from the video data recorded on the recording medium 420, and the reproduction is started. Next, a reproduction mode setting process 272 is performed. The playback mode is set to one of two modes, a normal playback mode and a high-speed playback mode. If the reproduction speed | Vp | ≦ 1, the normal reproduction mode is set, and if | Vp |> 1, the high-speed reproduction mode is set. Here, Vp = 1 means normal playback speed (1 × speed), Vp = 0 means still (stop), and Vp <0 means reverse playback. 0 <Vp <1 indicates low-speed forward reproduction at less than 1 × speed, but low-speed forward reproduction is shorter in decoding processing time than normal reproduction, and can be dealt with by controlling frame transmission from the video reproduction means 450 to the display device 432. Therefore, the normal playback mode is set. Although -1 ≦ Vp <0 indicates low-speed reverse playback at 1 × speed or less, by providing a video buffer 450 with a memory buffer for storing decoded frames and prefetching data for GOPs, the decoding processing capacity can be improved. Since it is possible to deal with this, in the present embodiment, description will be made assuming that the normal playback mode is included.
[0017]
When the reproduction mode setting processing 272 is completed, the decoding processing 230 in the normal reproduction mode or the decoding processing 200 in the high-speed reproduction mode is performed through the reproduction mode determination processing 284. In these processes, the frame decoding process is continued in the playback mode until a change in the playback mode is detected. If the playback mode changes, stop determination processing 280 is performed. If the playback is not stopped, that is, if Vp = 0, the process returns to the playback mode determination processing 284. If the playback is stopped, the playback processing ends at 290.
[0018]
The decoding process 230 in the normal playback mode will be described with reference to the flowchart in FIG. First, normal decoding 240 of the frame and output 241 of the frame are performed. Step 240 is a general decoding process of the MPEG stream, and decodes the next frame in the encoding order in the stream. Step 241 is a process of outputting a corresponding next time-ordered frame from the decoded frames. When the normal decoding 240 of the frame and the output 241 of the frame are completed, since the time required for decoding one frame has elapsed, processes 280 and 282 for detecting whether or not the reproduction speed Vp has been changed by a user operation are performed. . In step 280, if not stopped, that is, if Vp = 0, the process proceeds to the next determination. If Vp = 0, the process ends at 250. In step 282, it is detected whether or not the reproduction speed has changed to the high-speed reproduction mode. If | Vp |> 1, the processing 271 for setting the high-speed reproduction mode is performed, and the processing ends. If Vp is outside the range, the normal reproduction mode is continued, and the process returns to the normal decoding 240 for the next frame.
[0019]
The decoding process 200 in the high-speed playback mode will be described with reference to the flowchart in FIG. First, a decoding area setting process 300 for the reproduction speed Vp is performed. This is to set an area of a frame to be decoded within a certain period of time from the present time according to the playback speed Vp and the decoding processing capability of the video playback unit 450. Next, decoding 210 of the frame in the decoding area is performed on the set decoding area. An output area selection 211 is performed on the decoded data in the decoding area in consideration of the reproduction speed Vp and the visibility. The selected area is output for display at the frame output 241. Next, processing 280 and 281 for detecting whether or not the reproduction mode has changed is performed. In step 280, it is determined whether the reproduction speed is Vp = 0. In step 281, if the reproduction speed is | Vp | ≦ 1, the normal reproduction mode is set. Therefore, in step 270, the normal reproduction mode is set and the processing ends.
[0020]
The concept of the setting 300 of the decoding area for the reproduction speed Vp will be described with reference to FIG. The MPEG stream 100 includes an intra-coded frame (I frame) 101 and an inter-coded frame (P frame) 102. Here, the inter-frame coded frame 102 may include a B frame. In the MPEG stream 100, starting from the I frame located at the head of the GOP, the decoding area is reduced in the vertical direction by the maximum value of the vector search range in the vertical direction and the value 110 determined by the search speed / decoding processing capacity. 111 is set. At this time, since the area of the decoding area 111 corresponds to the decoding processing amount, the area of the decoding area at the reproduction speed Vp is adjusted so as to fall within the range of the decoding processing capability of the video reproducing means 450. In the output area selection 211 in the next step, the frame data 103 whose display is to be updated is selected from the slice data included in the decoding area 111.
[0021]
A method of calculating the value 110 determined by the maximum value of the vector search range in the vertical direction and the search speed / decoding processing capability will be described using the example of FIG. FIG. 6A shows an MPEG stream composed of only I and P frames with GOP length N = 6. The frame size is assumed to be 480 pixels vertically × 720 pixels horizontally. When each frame is divided in the vertical direction from the viewpoint of decoding processing, the slice unit is the minimum unit. In a general case where there are only 480 pixels in the vertical direction and only one slice exists in the horizontal direction, since 30 slices exist in each frame, it is determined for each frame whether 30 slices are included in the decoding area. Will be set. In the example shown in the figure, for simplicity, it is assumed that six slices are combined and five divided regions are the minimum unit.
[0022]
It is assumed that the playback speed is quadruple speed playback, that is, Vp = 4, and the average decoding speed Vd = 2 as the decoding processing capability. Vd = 2 means that two frames can be decoded in one frame time. When all frames are decoded by a normal method, a minimum of Vd = 4 is required. Therefore, when Vd = 2, high visibility and smooth reproduction cannot be performed. Under this condition and the condition that the maximum value of the vector search range in the vertical direction is 96 pixels or less, a decoding area can be set as in the setting example of FIG. The shaded area in the figure is the decoding area, and the area is two frames per one frame time according to the decoding processing capacity. Further, in order to enhance the visibility, the area reduction from above and the area reduction from below are performed alternately.
[0023]
The reason why the maximum value of the vector search range in the vertical direction is 96 pixels or less is to ensure that, when referring to the preceding frame, a divided region that is separated by two or more, that is, a region that has not been decoded is not referenced. . From this point, if the number of divided regions to be decoded is reduced by one for each frame, decoding can be performed normally. Also, the value of the vector search range can be calculated by referring to the value of f_code included in the MPEG header, for example. In this example, the number of pixels is set to 96 pixels or less in one frame. However, in normal coding, motion search is not performed in such a large range. In an actual operation, a decoding unit can be dynamically allocated by, for example, reducing a divided region for two slices for a frame whose motion does not fit into 16 pixels in the slice unit, based on a slice unit. .
[0024]
The operation when the reproduction speed Vp changes will be described with reference to FIG. FIG. 7A shows a diagram of the decoding area in FIG. 6B. When the reproduction speed Vp increases as shown in FIG. 7B, the width of one frame time in FIG. 7A increases, and the average decoding speed Vd does not change. Will decrease. Conversely, when Vp decreases as shown in FIG. 7C, the ratio of the area of the decoding area increases. In any of the examples, the decoding processing speed is constant at Vd = 2. Thus, the decoding area is set within the range of the decoding processing speed.
[0025]
The output area selection 211 will be described with reference to FIG. FIG. 8A shows the decoding area obtained in FIG. 6B. At each frame time, a divided area is selected from a plurality of frames so as to enhance the visibility at the time of search, and an output frame for quadruple speed reproduction shown in FIG. 8B can be obtained. The divided area selected in (a) is not limited to whether or not it is included in each frame time, and can be freely selected from the viewpoint of improving visibility.
[0026]
FIG. 9 shows an example of processing on an MPEG stream composed of I, P, and B frames. As in the example of FIG. 6, the reproduction speed Vp = 4, the average decoding speed Vd = 2, and the GOP length N = 6. Since the order of prediction differs from that in the example of FIG. 6, the number of divided regions is reduced according to the order of prediction in the I, P, and B frames. FIG. 9A shows a setting example of the decoding area. The area of the decoding area is two frames per one frame time. FIG. 9B shows an example of selecting an output area.
[0027]
In the present embodiment, the fast forward reproduction in the forward direction has been described as an example. However, for the fast forward reproduction in the backward direction, the decoding process is performed by pre-reading the frames for the GOP and storing the decoded frames in the memory. In terms of capabilities, it can be realized with a similar concept. Further, in the present embodiment, the shape of the divided region is a horizontal slice from the viewpoint of decoding processing, but other shapes such as vertical division are also possible. FIGS. 6 and 9 show examples of the method of setting the decoding area. However, any method of setting the area based on the information on the reproduction speed, the average decoding speed, and the search range of the vector may be used. It is not restricted to.
[0028]
In the above description, the average decoding processing speed of 2 × speed is assumed, but it is apparent that the same can be applied to the case of n × speed (n is an integer of 2 or more). In the example, the average decoding speed of the I, P, and B frames is assumed to be the same. However, common processing such as inverse DCT and variable-length decoding, vector / motion compensation processing specific to the P and B frames, and macro It is also possible to set a decoding area by setting an average decoding speed for each of I, P, and B frames in consideration of block skip processing and the like. Further, it is apparent that the present invention can be applied to a stream in which the GOP length N and the configuration of the GOP are variable.
[0029]
An advantage of the present invention is that it can be applied to high-speed playback of general MPEG streams. That is, intra coding for high-speed reproduction is not required. In addition, since the decoding area can be set within the range of the decoding processing capability according to the reproduction speed, smooth reproduction can be performed without causing a phenomenon such as a response not being maintained by the decoding processing. As described above, according to the present invention, in a high-speed reproduction of a video signal subjected to inter-frame predictive coding, a search operation with high visibility that maximizes decoding processing capability within a range in which a video can be reproduced smoothly. Can be realized.
[0030]
(Embodiment 2)
In the present embodiment, an apparatus for implementing Embodiment 1 will be described.
[0031]
FIG. 10 is a diagram showing a video playback device of the present invention. In the video reproducing apparatus 400 of FIG. 10, reference numeral 410 denotes a decoder for decoding a stream which is an encoded video, 411 denotes a CPU for performing a decoding process, and 412 denotes a memory for recording the stream and the decoded frame. Reference numeral 413 denotes a ROM for storing a program for operating the CPU 411 in an initial state; 421, a disk controller for driving a disk; 422, an optical disk drive on which a stream is recorded; 431, a disk controller 421 and a decoder 410; Is a display device for displaying images, such as a monitor.
[0032]
The operation of the video reproducing apparatus configured as described above will be described below. First, before starting the video reproducing apparatus, a program for decoding according to the present invention is recorded in the ROM 413. By starting the apparatus, a program is loaded from the ROM 413 to the CPU 411, and the CPU 411 can perform stream decoding processing. The decoding process in the video reproducing means 450 according to the present invention is realized by this program. Before playback, the optical disk on which the stream is recorded is loaded into the optical disk drive 422.
[0033]
The playback operation of the video playback device according to the present invention will be described with reference to FIG. When a playback command from the user is given to the control processor via the bus 433, the control processor 431 drives the disk controller 421, reads a certain amount of streams starting from the specified time from the optical disk drive 422, and transfers them to the memory 412. I do. This fixed amount can be set to an appropriate length, for example, a unit of several GOPs or a unit of seconds so as not to cause a failure in the reproduction operation. At the same time, a decoding instruction to the CPU is written in the interrupt area of the memory 412. The CPU 411 monitors an interrupt area of the memory 412. When a reproduction command is given, the CPU 411 reads a stream from the memory 412, performs a decoding process, and writes the decoded frame data to the memory 412. When the frame data is written to the memory 412, the control processor 431 sends it to the display device 432, and the video is displayed.
[0034]
The program has a decoded data presence flag indicating whether or not the decoded frame data exists in the memory 412, and a table of the index (serial number uniquely determined in the sequence) of the corresponding frame. To keep. This table can be easily managed by updating the flag when the frame is decoded and stored in the memory 412. The memory 412 stores frame data corresponding to the index. The control processor 431 in FIG. 10 can check whether the decoded frame data exists in the memory by checking the index on the memory 412. By using the memory as described above, data of one or more GOPs can be pre-read, decoded, and stored in the memory, and it is possible to cope with reverse reproduction or reverse high-speed reproduction.
[0035]
In the above description of the video reproducing apparatus, the description has been made on the assumption that the optical disk drive is used. However, it is needless to say that the same can be realized with a medium for recording information such as a hard disk drive or a memory. Although an example using a CPU and a memory as a decoder has been described, the present invention is not limited to this. As described above, according to the present embodiment, Embodiment 1 can be realized as an apparatus.
[0036]
【The invention's effect】
As is clear from the above description, according to the present invention, a search operation with high visibility that maximizes the decoding processing capability can be realized within a range in which a video can be smoothly reproduced.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing a video reproducing method according to Embodiment 1 of the present invention.
FIG. 2 is a configuration diagram for realizing a video reproduction method according to the first embodiment;
FIG. 3 is a flowchart showing decoding processing during reproduction according to the first embodiment;
FIG. 4 is a flowchart showing a decoding process in a normal reproduction mode according to the first embodiment;
FIG. 5 is a flowchart showing decoding processing in a high-speed playback mode according to the first embodiment;
FIG. 6 is a diagram showing a setting example of a decoding area according to the first embodiment;
FIG. 7 is a diagram showing a setting example of a decoding area with respect to a change in a reproduction speed in the first embodiment;
FIG. 8 is a diagram showing an example of selecting an output area according to the first embodiment;
FIG. 9 is a diagram showing a setting example of a decoding area and an output area in the first embodiment.
FIG. 10 is a diagram showing a configuration of a video playback device according to Embodiment 2 of the present invention.
FIG. 11 is a view for explaining conventional MPEG encoding.
FIG. 12 is a diagram illustrating encoding of only conventional MPEG I and P frames.
FIG. 13 is a view for explaining conventional 4 × speed reproduction of MPEG.
FIG. 14 is a view for explaining a conventional method for improving the visibility of MPEG.
[Explanation of symbols]
100 MPEG stream
101 I frame
102 P frame
103 Frame data for updating display
110 Maximum value of vector search range in vertical direction, value determined by search speed, decoding processing capacity
111 decoding area
200 High-speed playback mode decoding
210 Decoding frame in decoding area
211 Select output area
220 End of high-speed playback mode
230 Decoding process in normal playback mode
Normal decoding of 240 frames
Output of 241 frames
250 End of normal playback mode
260 Playback processing
270 Set normal playback mode
271 Set high-speed playback mode
290 End of playback processing
300 Decoding area setting for playback speed
400 video playback device
410 decoder
411 CPU
412 Memory (RAM)
413 ROM
414 bus
415 CPU core
416 Program Cache
417 Data Cache
418 Program bus
419 Data bus
420 recording medium
421 Disk Controller
422 Optical Disk Drive
431 control processor
432 Display device
433 bus
440 Reproduction operation input means
450 Video playback means

Claims (8)

A video playback method for playing back a video from a recording medium on which an encoded video is recorded,
The average decoding time required for decoding the frame is calculated, and at least n (n is an integer of 1 or more) or more frames to be reproduced within a fixed time from the current time are divided into k (k is an integer of 2 or more) frames. A video that has a decoding step of selecting and decoding m (m is an integer equal to or greater than 1) areas that can be decoded within the average decoding time from the n * k areas by dividing the area into n areas; Playback method. The video is an inter-frame predictive encoded video,
2. The decoding step according to claim 1, wherein, when the m regions are selected, decoding is performed such that a region referred to by a prediction vector in the m regions is always included in the m regions. Video playback method. 3. The video reproducing method according to claim 2, wherein the decoding step dynamically changes the value of m based on the average decoding time and a video reproducing speed. 4. The decoding step according to claim 2, wherein an arbitrary area necessary for performing reproduction display at the reproduction speed is selected as an output area from the m areas. Video playback method. A video playback device that plays back a video from a recording medium that records an encoded video,
The average decoding time required for decoding the frame is calculated, and at least n (n is an integer of 1 or more) or more frames to be reproduced within a fixed time from the current time are divided into k (k is an integer of 2 or more) frames. Video playback comprising a decoder that divides into n regions and selects and decodes m (m is an integer of 1 or more) regions that can be decoded within the average decoding time from the n * k regions. apparatus. The video is an inter-frame predictive encoded video,
6. The decoder according to claim 5, wherein, when selecting the m regions, the decoder performs decoding such that a region referred to by a prediction vector in the m regions is always included in the m regions. Video playback device. 7. The video playback device according to claim 6, wherein the decoder dynamically changes the value of m based on the average decoding time and a video playback speed. 8. The decoder according to claim 6, wherein the decoder selects, as an output area, an arbitrary area necessary for performing reproduction display at the reproduction speed from the m areas. Video playback device.

Images