Video file format classification
Generalized video files can be subdivided into two categories, namely animation files and video files. Animation file refers to an image sequence composed of several interrelated still images, which are continuously played to form a group of animations, and are usually used to complete a simple dynamic process demonstration. Image files mainly refer to those multimedia files that contain real-time audio and video information. Their multimedia information usually comes from video input devices. Because it contains a lot of audio and video information at the same time, image files are often quite large, often several MB or even dozens of MB.
1. animation file
GIF file. GIF format
GIF is the abbreviation of Graphics Interchange Format, which is a color image file format with high compression ratio introduced by CompuServe Company in 1980s. CompuServe is a famous online information service organization in the United States. In view of the limitation of network transmission bandwidth at that time, CompuServe Company adopted LZW(Lempel? Ziff & ampWelch algorithm, introduces the GIF image format, which is mainly used for network transmission of image files. Because the size of GIF image file is usually several times smaller than other image files (such as PCX), this image format has been widely used quickly. Considering the actual situation in network transmission, GIF image format adds a gradual display mode in addition to the general progressive display mode, that is, in the process of image transmission, users can first see the general outline of the image, and then gradually see the details of the image as the transmission process continues, thus adapting to the user's viewing psychology. This mode has been adopted by other image formats in the future, such as JPEG/JPG. At first, GIF was only used to store a single still image, which was called GIF87a. Later, it was further developed into GIF89a, which can store multiple still images at the same time and then form a continuous animation. At present, most of the color animation files used on the Internet are GIF files in this format.
Flic file. fli/。 flc
Flic file is a color animation file format adopted by Autodesk Company in its 2D/3D animation software such as Autodesk Animator/Animator Pro/3D Studio, in which FLC is an original animation file format based on 320×200 resolution, and. FLC is. FLI, using more efficient data compression technology, the resolution is no longer limited to 320×200. Flic file uses run-length coding algorithm and incremental algorithm for lossless data compression. Firstly, the first image in the whole animation sequence is compressed and saved, and then the difference or change part of two adjacent images is calculated frame by frame, and this part of data is RLE compressed. Because the difference between adjacent images in an animation sequence is usually small, run-length coding can achieve a fairly high data compression rate.
GIF and Flic files are usually used to represent computer-generated animation sequences, and their images are relatively simple, so they can obtain higher lossless compression rate and smaller file size. However, for the real and complex image information, lossless compression is powerless. Even with efficient lossy compression algorithm, the size of the image file is still quite large.
2. Image files
AVI file. AVI
AVI, the abbreviation of Audio Video Interleaved, is a digital audio and video file format developed by Microsoft Company that conforms to RIFF file specification. Originally used in Microsoft video for Windows (VFW) environment, it has been directly supported by most operating systems such as Windows 95/98 and OS/2. AVI format allows video and audio to be played alternately and synchronously, and supports 256 colors and RLE compression. However, there is no compression standard for AVI files. Therefore, the AVI file format is only used as a standard on the control interface and is not compatible. AVI files generated by different compression algorithms must use the corresponding decompression algorithm to play. Commonly used AVI players are mainly Microsoft's Video for Windows or Windows 95/98' s Video 1, and Intel's Indeo Video. At present, AVI files are mainly used in multimedia CDs to save various image information such as movies and TV, and sometimes appear on the Internet for users to download and enjoy the wonderful clips of new movies.
QuickTime file. mov/。 quart
QuickTime is an audio and video file format developed by Apple Computer Company, which is used to save audio and video information. It has advanced video and audio functions, and is supported by all mainstream computer platforms, including Apple Mac OS and Microsoft Windows 95/98/NT. QuickTime file format supports 25-bit color, RLE, JPEG and other leading integrated compression technologies, and provides video effects over 150, and is equipped with sound equipment, providing more than 200 MIDI-compatible audio and equipment. The new version of QuickTime further expands the original functions, including the key functions of Internet-based applications, and can provide real-time digital information flow, workflow and file playback functions through the Internet. In addition, QuickTime also adopts a virtual reality technology called QuickTime VR (QTVR). VR) technology, users can observe the 360-degree scene around a place or an object from any angle in space through the interactive control of mouse or keyboard. QuickTime has been widely recognized by the industry for its leading multimedia technology and cross-platform characteristics, small storage space requirements, independence of technical details and high openness of the system, and has now become the de facto industry standard in the field of digital media software technology. The International Organization for Standardization (ISO) recently chose QuickTime file format as MPEG? Standard unified digital media storage format.
MPEG file mpeg/。 mpg/。 Digital audio tape)?DOS file name data file
MPEG file format is the international standard of moving image compression algorithm. It uses lossy compression to reduce redundant information in moving images and ensure the dynamic refresh rate of 30 frames per second. Almost all computer platforms support it. MPEG standard includes three parts: MPEG video, MPEG audio and MPEG system (video and audio synchronization). The MP3 audio file mentioned above is a typical application of MPEG audio, while Video Disc (VCD), Super VCD (SVCD) and DVD (Digital Versatile Disc) are new consumer electronic products produced by MPEG technology. MPEG compression standard is designed for moving images. The basic method is to collect and save the information of the first frame in unit time, and then only store the changes of the rest frames relative to the first frame, so as to achieve the purpose of compression. It mainly adopts two basic compression technologies: motion compensation technology (predictive coding and interpolation coding) to realize time compression and transform domain (discrete cosine transform DCT) to realize space compression. The average compression ratio of MPEG is 50∶ 1, and the highest compression ratio is 200∶ 1. The compression efficiency is high, and the image and sound quality are also good. Moreover, MPEG has a unified standard format on the microcomputer, and its compatibility is quite good.
Real time video file. space
RealVideo file is a new streaming video file format developed by RealNetworks, which is included in the audio and video compression standard RealMedia developed by RealNetworks. It is mainly used for real-time transmission of moving video images on low-speed WAN, and different compression ratios can be adopted according to different network data transmission rates to realize real-time transmission and real-time playback of image data. RealVideo can not only be played in the form of ordinary video files, but also be downloaded and played with the RealServer server during data transmission, instead of having to download and then play them like most video files. At present, many websites on the Internet have used RealVideo technology to broadcast major events live.
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With the rapid development of computer software and hardware technology and broadband Internet technology, various video recording and post-production technologies have also developed by leaps and bounds. Traditional video (for example. AVI and. MPEG format) is generally large in size and poor in definition, such as VCD format played in computers. However, now, the same video can not only be several times smaller than the original one, but also be immersive with ultra-high-definition effect, which makes us have to sigh and thank the ever-changing technology for its benefits to our lives! The reality is far more than that. With the help of broadband internet technology and a multimedia technology called "streaming video", ordinary people can access any video materials they need conveniently and quickly, and users can preview any specified segment of the video materials without downloading the whole or the whole video!
We can analyze the development and changes of video from two aspects: the ultra-high definition of video is of course the result of the continuous upgrading of video recording equipment, while the sharp reduction of video volume and the improvement of streaming video file transmission performance benefit from the continuous innovation and improvement of video compression technology and video editing and processing technology, which is manifested in video format at the macro level.
At present, video formats can be divided into two categories: local video suitable for local play and network streaming video suitable for network play. It is worth mentioning that although the latter may not be as good as the former in terms of playback stability and playback quality, the wide spread of online streaming video makes it widely used in the fields of Internet information services such as video on demand, network demonstration, distance education and online video advertising.
I. Local video
●AVI format: its English full name is Audio Video Interleaved, that is, audio and video interleaved format. It was introduced by Microsoft in 1992, and is known and familiar with people together with Windows3. 1. The so-called "audio and video interleaving" means that video and audio can be intertwined and played simultaneously. The advantage of this video format is that it has good image quality and can be used across multiple platforms. Its disadvantage is that it is too big, and what is worse is that the compression standard is not uniform. The most common phenomenon is that the high version of Windows media player can't play the video in AVI format edited in the early stage, and the low version of Windows media player can't play the video in AVI format edited in the latest stage. Therefore, when we play some videos in AVI format, there are often some puzzling problems. For example, the video can't be played because of the video coding problem, or even if it can be played, there are some puzzling problems, such as the inability to adjust the playback progress, and only sound without images when playing. If users encounter these problems when playing video in AVI format, they can solve them by downloading the corresponding decoder.
●nAVI format: nAVI is the abbreviation of newAVI, which is a new video format developed by an underground organization called ShadowRealm (it has little to do with the AVI format mentioned above). It is modified from Microsoft ASF compression algorithm, but it is different from the ASF video format in the network video introduced below. It greatly improves the definition of ASF video files by increasing the frame rate at the expense of the video "streaming" characteristics of the original ASF video files.
●DV-AVI format: The full English name of DV is Digital Video Format, which is a family digital video format jointly proposed by Sony, Panasonic, JVC and other manufacturers. At present, very popular digital cameras use this format to record video data. It can transmit video data to the computer through the IEEE 1394 port of the computer, and can also record the edited video data from the computer back to the digital camera. The file extension of this video format is usually. Avi, so it is also called DV-AVI format.
●MPEG format: Its full English name is Moving Picture Expert Group, that is, moving picture expert group format, which is the format of VCD, SVCD and DVD that people often watch at home. MPEG file format is the international standard of moving image compression algorithm. It uses lossy compression method to reduce redundant information in moving images. To put it more clearly, MPEG compression method is based on the fact that two adjacent images are mostly the same, and the redundant parts in the latter image and the previous image are removed, so as to achieve the purpose of compression (the maximum compression ratio can reach 200: 1). At present, there are three compression standards of MPEG format, namely MPEG- 1, MPEG-2 and MPEG-4. In addition, MPEG-7 and MPEG-2 1 are still in the research and development stage.
MPEG- 1: formulated in 1992, it is an international standard designed for digital storage media moving images and audio coding with data transmission rate below 1.5Mbps, which is also the VCD production format we usually see. Using the compression algorithm of MPEG- 1, a movie with the length of 120 minutes can be compressed to the size of1.2gb. The file extensions of this video format include. mpg，。 mlv，。 mpe，。 Mpeg and. Dat file in VCD.
MPEG-2: Based on 1994, the design goal is advanced industrial standard image quality and higher transmission rate. This format is mainly used for DVD/SVCD production (compression), as well as some HDTV (high definition television broadcasting) and some demanding video editing and processing. With the compression algorithm of MPEG-2, a movie with a length of 120 minutes can be compressed to a size of 4 to 8GB. The file extensions of this video format include. mpg，。 mpe，。 mpeg，。 M2v and. Vob file on DVD.
MPEG-4:MPEG-4 was established by 1998 and is specially designed for playing high-quality video of streaming media. It can compress and transmit data with extremely narrow bandwidth through frame reconstruction technology, and obtain the best image quality with the least data. At present, the most attractive feature of MPEG-4 is that it can save small-capacity video files close to DVD quality. In addition, this file format also contains some special functions, such as bit rate scalability, animation wizard, interactivity and even copyright protection, which are not available in previous MPEG compression standards. The file extensions of this video format include. asf，。 Mov and DivX AVI
Tip: Careful users must have noticed that there is no MPEG-3 coding in the middle. In fact, the familiar MP3 is MPEG-3 (MPEG layeur 3) coding.
●DivX format: This is another video coding (compression) standard derived from MPEG-4, commonly known as DVDrip format. It adopts MPEG-4 compression algorithm and integrates MPEG-4 and MP3 technologies. To put it bluntly, it is a video format formed by using DivX compression technology to compress the video image of DVD with high quality, compressing the audio with MP3 or AC3, and then combining the video and audio with the corresponding plug-in subtitle files. Its picture quality is almost the same as that of DVD, and its volume is only a fraction of that of DVD. This kind of coding has low requirements for machines, so DivX video coding technology can be said to be a new video compression format that poses the greatest threat to DVD, and it is called DVD killer or DVD terminator.
●MOV format: A video format developed by Apple. The default player is Apple's QuickTimePlayer. It has the characteristics of high compression ratio and perfect video definition, but its biggest feature is cross-platform, that is, it can support not only MacOS but also Windows series.
Second, the network video
●ASF format: its English full name is Advanced Streaming format, which is a video format launched by Microsoft to compete with the current Real Player. Users can play directly with Windows Media Player that comes with Windows. Because it uses MPEG-4 compression algorithm, the compression rate and image quality are very good (high compression rate is beneficial to the transmission of video stream, but the image quality will definitely be lost, so sometimes the image quality of ASF format is not as good as that of VCD).
●WMV format: Its full English name is Windows Media Video, which is also a file compression format introduced by Microsoft. It adopts independent coding mode and can directly watch video programs online in real time. The main advantages of WMV format include: local or network playback, extensible media types, component download, extensible media types, stream priority, multilingual support, environmental independence, rich inter-stream relationships and scalability.
●RM format: The audio and video compression standard developed by Real Networks Company is called Real Media. Users can use RealPlayer or RealOne Player to play network audio and video resources that meet the technical specifications of RealMedia. RealMedia can set different compression ratios according to different network transmission rates, so as to realize real-time transmission and playback of image data on low-rate networks. Another feature of this format is that users can use RealPlayer or RealOne Player to realize play online without downloading audio and video content. In addition, RM, as the mainstream network video format at present, can also convert videos in other formats into RM videos through its Real Server server, which is responsible for publishing and playing. RM and ASF formats can be said to have their own advantages. Generally, RM video is soft, while ASF video is relatively clear.
●RMVB format: This is a new video format, which is upgraded and expanded from RM video format. Its advantage lies in that the RMVB video format breaks the average compressed sampling mode of the original RM format, and makes reasonable use of the code rate resources on the basis of ensuring the average compression ratio, that is to say, static scenes with little action can leave more bandwidth space, and when there are fast-moving scenes, these bandwidths will be utilized. In this way, on the premise of ensuring the quality of still images, the image quality of moving images is greatly improved, thus achieving a delicate balance between image quality and file size. In addition, compared with DVDrip format, RMVB video also has obvious advantages. If a DVD movie of about 700MB is transcribed into RMVB format with the same audio-visual quality, its size will be about 400MB at most. Not only that, this video format also has the unique advantages of built-in subtitles and no plug-in support. If you want to play this video format, you can use RealOne Player2.0 or RealPlayer8.0 plus RealVideo9.0 or above.
Common video file formats
Watching VCD by computer is the most popular thing in recent years, and it is also a preliminary demonstration of the powerful multimedia function of computer. Now, you can watch not only VCD but also DVD on your computer. Streaming media formats such as RM, WMV and ASF, which have emerged and been widely accepted in recent two years, have become the favorite of every netizen. However, in order to fully enjoy the fun these video files bring us, you should first understand their characteristics and differences.
ASF ASF (Advanced Streaming format) is a file compression format specially developed by Microsoft in order to compete with Real player for the streaming media market, which can watch video programs on the Internet in real time. It adopts the compression algorithm of MPEG-4, so its compression rate and image quality are very good. However, because it is a streaming media format, the bandwidth is limited when making it, so its picture quality is worse than that of MPEG 1 standard VCD disc (but the file size is much smaller) and better than RM format. Because of the strong support of Microsoft Windows Media Player, although the launch time is not long, its influence is not small.
AVI AVI is the abbreviation of audio-video interleaving. As the name implies, it can interweave video and audio and play them simultaneously. AVI format can be regarded as the patriarch of video format, which has played an important role since the era of Windows3. 1. I believe everyone likes the title of the game in AVI format. Its characteristics are good compatibility, high image quality, but large volume. However, Microsoft has always had a soft spot for AVI for so many years, and naturally it will not give up easily. After the introduction of MPEG-4 format, Microsoft also designated the suffix of video files supporting the latest MPEG-4 compression standard as AVI, which made this ancient video format glow with new brilliance.
MOV is an audio and video file format developed by Apple, and its dedicated player is QuickTime. MOV used to only support Apple Macintosh system series, but now it also supports Windows series operating systems. MOV format supports 25-bit color, various video effects and various MIDI-compatible audio, and the video effect is very good. Generally speaking, this format is used for Hollywood movie trailers that we download from the Internet.
N AVI is the abbreviation of newAVI, which is a new video format developed by an underground organization called ShadowRealm. On the basis of ASF compression algorithm, the image quality of ASF format is improved, and NAVI can have a higher frame rate. But in this way, nAVI actually becomes an improved ASF format, without the characteristics of video streaming, which is more suitable for local playback.
RM/RA RA/RAM (Real Video/Audio) format is a very popular streaming video/audio format on the Internet. Before ASF/WMA appeared, they were the leaders of video streaming technology. It can dial-up the Internet using a 56K modem, and users can receive streaming video and audio in real time. Speed naturally brings about a decline in image quality/sound quality. Compared with ASF, RM video is softer in color and ASF video is relatively clear.
MPEG 1 MPEG is the abbreviation of moving picture expert group, including mpeg1,MPEG2 and MPEG4. The MPEG- 1 standard was formulated in 1992, which is an international standard for the coding design of moving images and audio of digital storage media with data transmission rate below 1.5Mbps. It is mainly used to store color synchronous moving video images in CD-ROM (including Video-CD, CD-I, etc. ), but also for SIF (standard exchange format) standard resolution (NTSC system is 352. PAL system is 352×288), which can play 30 frames per second, and has the sound quality of CD (compact disc), and the quality level is basically equivalent to VHS. At the same time, it is also used for video transmission on digital telephone network, such as ADSL, VOD, education network, etc.
With the compression algorithm of MPEG- 1, a movie with a length of 120 minutes can be compressed to about 1.2GB, so it is widely used in VCD production and downloading of some video clips. It can be said that 99% of VCDs are compressed in MPEG- 1 format (Note: VCD2.0 does not mean that VCDs are all based on MPEG.
MPEG-2 MPEG-2 standard is formulated in 1994, which is an international standard for moving images and their audio coding, and the data transmission rate is 3~ 10Mbps. MPEG2 can provide a wide range to change the compression ratio to meet the requirements of different image quality, storage capacity and bandwidth. At the same time, on the basis of compatibility with MPEG 1, low bit rate and multi-channel expansion can be realized: MPEG2 can compress a movie of 120 minutes to 4~8GB, of course, it provides DVD quality; MPEG2-2 audio coding can provide left, right, middle and two surround channels, as well as an emphasized bass channel and up to seven channels (DVD can be dubbed in eight languages).
In addition to being the designated standard for DVD, MPEG2-2 can also be used to provide broadcast-grade digital video for broadcasting, cable TV networks, cable networks and direct broadcast satellites. But for ordinary users, due to the limitation of TV resolution, the high-definition picture quality (such as DVD picture) brought by MPEG2-2 is not obvious on TV, but its audio characteristics (such as emphasizing bass and multi-channel) have been widely used.
MPEG3 Actually, MPEG3 is a standard that was abandoned before it was born. It was originally the coding and compression standard of HDTV (High Definition Television Broadcasting), but due to the excellent performance of MPEG-2, MPEG-3 is unnecessary. The MP3 we usually talk about is not MPEG3, but MPEG Layer 3, which is just an audio compression standard of MPEG.
MPEG-4/Divx MPEG-4 was released in June 1998 1 1. The international standard MPEG-4 1999 1, which was originally expected to be put into use in June, is not only aimed at video and audio coding at a certain bit rate, but also pays attention to the interactivity and flexibility of multimedia systems.
The transmission rate of MPEG4-4 is 4800-64000 bit/s, and the resolution is 176× 144. It can compress the transmitted data through the extremely narrow bandwidth frame reconstruction technology, and obtain the best image quality with the least data. Therefore, it can play an important role in digital TV, dynamic images, Internet, real-time multimedia monitoring, mobile multimedia communication, video streaming and visual games on Internet/Intranet, interactive multimedia applications on DVD and so on.
Of course, for ordinary users, the most attractive thing about MPEG-4 is that it can achieve the quality of DVD on ordinary optical discs: a movie of 120 minutes can be compressed into a video stream of about 300MB by using MPEG-4 compression algorithm; DivX video coding technology with MPEG4-4 compression algorithm can compress 120 minute movie to about 600MB, or a DVD movie to two CD-ROMs. In other words, with MPEG4-4, you can enjoy similar video quality without buying DVD-ROM!
However, compared with DVD, MPEG-4 is a high-speed lossy compression algorithm, and the image quality can never be compared with MPEG-2 of DVD. After all, the storage capacity of DVD is relatively large. In addition, in order to ensure that the high-speed moving image is not distorted, there must be enough bit rate. Recently, although the bit rate of MPEG4-4 can be adjusted to be similar to that of DVD, the overall effect is not small. Therefore, the current MPEG4-4 can only be used in the entertainment and appreciation market, and those professional video fields with high quality requirements cannot be adopted for the time being.
Audio format
1.WAV format is a sound file format developed by Microsoft, also known as waveform sound file. It is the earliest digital audio format and is widely supported by Windows platform and its applications. WAV format supports a variety of compression algorithms, various audio bits, sampling frequencies and channels, the sampling frequency is 44. 1kHz, and the quantization bit is 16 bits. Like CD, it needs too much storage space to communicate and spread.
2.MIDI is the abbreviation of musical instrument digital interface, also known as musical instrument digital interface, which is a unified international standard for digital music/electronic synthetic musical instruments. It defines the way in which electronic devices such as computer music programs and digital synthesizers exchange music signals, and specifies the cables, hardware and data transmission protocols between electronic musical instruments from different manufacturers and computers, which can simulate the sounds of various musical instruments. MIDI files are files in MIDI format, and some instructions are stored in MIDI files. Send these instructions to the sound card, and the sound card will synthesize sound according to the instructions.
Everyone is familiar with the music format of CD, with the extension of CDA. Its sampling frequency is 44. 1kHz, 16 quantized bits, which is the same as WAV, but the CD is stored in the form of audio track, also known as the "red book" format, which records the waveform stream, which is an approximate lossless format.
4. The full name of 4.MP3 is MPEG- 1 Audio Layer 3, which was incorporated into the MPEG specification in 1992. MP3 can compress digital audio files with high quality and low sampling rate. In other words, audio files (mainly large files, such as WAV files) can be compressed to a smaller extent, and the loss of sound quality is very small (the human ear simply does not notice this loss of sound quality).
5.MP3Pro was developed by Swedish coding technology company, including two major technologies: one is the unique decoding technology from coding technology company, and the other is the decoding technology jointly researched by French Thomson Multimedia Company, the patent holder of MP3, and Flawn Hof Integrated Circuit Association. MP3Pro can improve the original sound quality of MP3 music without changing the file size. It can compress audio files at a lower bit rate and maintain the sound quality before compression to the greatest extent.
6.WMA (Windows Media Audio) is the representative work of Microsoft in the field of Internet audio and video. WMA format aims to achieve a higher compression rate by reducing data traffic but maintaining sound quality, and its compression rate can generally reach 1: 18. In addition, WMA can also add anti-copy function through DRM (Digital Rights Management) scheme, or add restrictions on playing time and times, even playing machines, which can effectively prevent piracy.
7.MP4 is based on AT&T; A2b music compression technology with perceptual coding as the key technology is a new music format jointly released by American Network Technology Corporation (GMO) and RIAA. MP4 adopts the encoding technology of file copyright protection, which can only be played by specific users, effectively ensuring the legitimacy of music copyright. In addition, the compression ratio of MP4 reaches 1: 15, which is smaller than that of MP3, but the sound quality has not decreased. However, because only specific users can play such files, their circulation is far from that of MP3.
8.SACD (SA = Super Audio) was officially released by Sony. Its sampling rate is 64 times that of CD format, that is, 2.8224MHz, and SACD's playing frequency bandwidth is 100kHz, which is 5 times that of CD format. The 24-bit quantization digit far exceeds that of CD, and the sound details are richer and clearer.
9.QuickTime is a digital streaming media launched by Apple at 199 1. It is oriented to video editing, website creation and media technology platform. QuickTime supports almost all mainstream personal computing platforms and can provide real-time digital information flow, workflow and file playback functions through the Internet. The existing versions are QuickTime 1.0, 2.0, 3.0, 4.0 and 5.0. In version 5.0, many new technologies are also integrated, such as players that support the highest A/V playback quality.
10.VQF format is an audio compression technology jointly developed by Yamaha and NTT***, and its compression ratio can reach 1: 18. Therefore, the file volume after VQF compression is 30% ~ 50% smaller than that of MP3 under the same conditions, which is more convenient for online transmission and has excellent sound quality, close to CD (65438). However, VQF did not disclose the technical standards, so it has not been popularized so far.
1 1.DVD audio is a new generation of digital audio format with the same size and capacity as DVD video. It is a DVD disc with music format, and the sampling frequencies are "48kHz/96kHz/ 192kHz" and "44.1khz/88.2khz/176.4khz". Although the low sampling rates of 192kHz and 176.4kHz are dedicated to 2-channel playback, you can record up to 6 channels. However, recording with two channels of 192kHz/24b or six channels of 96kHz/24b can accommodate more than 74 minutes of recording, and the dynamic range is 144dB, which has an outstanding overall effect.
12. Sony MD(MiniDis