MP4 interpretation
Mp4, full name of MPEG-4 Part 14, is a multimedia computer file format using MPEG-4, with an extension of .mp4, which mainly stores digital audio and digital video. MP4 is a multifunctional player that integrates audio, video, picture browsing, e-books and radio. MP4 is bigger than MP3. The exact concept of MP4 is a long story, because the brand, market, product specifications and configuration standards of MP4 can all be described in one word-"chaos". I don't know if it's hype or fashion. In the eyes of merchants now, any player who can touch the video side is called MP4. This statement is simple and intuitive, and seems to be basically consistent with the author's vague understanding.
Audio MP4 format: AAC
MP4 is an audio format, which has nothing to do with MPEG-4, just as MP3 has nothing to do with MPEG-3. MP3 is the abbreviation of MPEG- 1 Audio Layer 3; MP4 is MPEG-2 AAC, which is a complete audio compression format, adding new functions such as perfect stereo reproduction, multimedia control and noise reduction. Most importantly, MP4 realizes digital copyright protection through special technology, which is incomparable to MP3.
Video MP4 format: MPEG-4
At present, most MP4s on the market prefer multimedia players, but few can play AAC. Some media even described MP4 as the abbreviation of MPEG4-4, which was a fallacy in the past, but this fallacy has become a truth after the constant hype of merchants. Now, if you go to the computer city and hear the word MP4, it is definitely the concept of a multimedia player that can play video format, not a walkman that can play audio MP4 AAC. This strange phenomenon is not without reason. As mentioned above, AAC has copyright protection function, which is why many record companies support AAC. In order to make their players support AAC, they have to support the payment of certain copyright fees or patent fees. In addition, the source of AAC is also a problem, which is not as public as MP3, and there are few online sources. Therefore, the development of audio MP4 player is not mature at present. In view of the above situation, many businesses simply "come back to life". Equating MP4 with the abbreviation of MPEG-4 just corresponds to the law that MP4 is the next generation MP3, which not only supports the music playing function of MP3, but also has powerful MPEG-4 video playing ability. In addition, it makes sense to equate MP4 with MPEG-4 just after "3".
MP4 is actually MP3 playing video.
In fact, this player is not MP4, but actually MP3. Video playback is only its subsidiary function, also called MP4, which is purely commercial speculation. This player has great limitations: the screen is very small (0.8~ 1.8 inches), the flash memory capacity is small, and it supports specific formats (MTV, MP4, MPV and DMV, etc.). ), and most of them use low-end screens such as organic light-emitting diodes and CSTN, so they can only be called MP3 which can accurately play videos. The representatives are DEC F 12R, Golden Colorful King, 3E 1000 and Pisa Colorful Airship.
Hard disk MP4
This kind of MP4 is the mainstream of development at this stage, and the number of products also occupies an absolute advantage. Simply put, the concept of hard disk MP4 is based on hard disk. A big belly can hold the whole world, and you don't have to worry about running out of space when using a hard disk. Generally speaking, hard disk MP4 also integrates many other functions, such as digital camera, video camera, tape recorder and digital companion ... This evaluation includes 1 1 hard disk MP4.
Flash MP4
Compared with hard disk MP4, flash MP4 uses flash memory as storage medium, and generally supports the expansion of internal flash card, usually SD card. There are two MP4s of this model in this evaluation, namely Govideo PMP- 120 and JXD-680. Flash memory MP4 is much smaller, lighter and several times cheaper.
MP4 without display screen
Some manufacturers think that the 3.5-inch screen of MP4 is too small to play high-quality video, and the flash memory of 128~256M of MP4 also makes people unable to enjoy blockbusters. Therefore, these manufacturers have designed a hard disk MP4 without a screen, which can be output to a TV and other screens through output terminals such as AV-OUT, and uses a 2.5-inch hard disk, which is too large. But for this kind of MP4 which does not emphasize mobility, it is much smaller than the traditional DVD player, and there are only a few models on the market. This MP4 has a capacity of tens of gigabytes, but the price is similar to that of flash memory MP4. For example, Bank of Communications MP4.
Various appellations about MP4
Although the concept of MP4 is divided into soft and hard, as far as hardware MP4 is concerned, it has different names according to different design standards or different functional emphases, such as MP4, PMP, PMC, PVP, PVR, PMA and so on.
MP4
A general concept with no unified definition, here is the concept of hardware MP4, which can be taken with you, the next generation MP3, all PMP, PMC, PVP, PVR and many other players.
PMP (portable media player)
There is no uniform standard, but production is based on the manufacturer's own requirements. For example, the software systems of iRiver PMP- 120 and PMP- 120 are all based on Linux, and the PMP system is generally developed by Linux, which has no fixed hardware and software requirements and can be combined at will, but this is also the reason for the diversification of MP4 products. In addition, the format compatibility and decoding ability of PMP are related to hardware, so it is difficult to upgrade.
PMC (portable media center)
The hardware and software of the platform are unified by Microsoft. The hardware is designated by Intel's XScale processor, while the software system is a Windows portable media player. The platform belongs to an open architecture, and the software is easy to expand. PMC is a new standard for Microsoft to enter the digital field of mobile entertainment. For example, YH-999 is in full compliance with PMC standards.
PVR (personal video recorder)
The main function of PVR is video recording. It can be said that PVR has powerful video recording function, and PVR generally has AV-IN/AV-OUT or video recording function. For example, Beatrice Twitch, Mustek PVR-H140.
Personal video player
Similar to the concept of PMP.
PMA (Pocket Media Assistant)
Simply speaking, it is the combination of PDA and hard disk MP4, which is a relatively trendy digital product. Aviva PMA 4XX series is the first and only PMA in the world that integrates personal entertainment, business applications and wireless Internet access.
Hardware architecture of MP4
The "core" of MP4 is dirty.
There is little difference between MP4 and MP3 in principle, but there is a big difference between them in hardware performance, mainly in video playback function, Divx and Xvid, etc. The playback of MPEG-4 requires the high processing power of CPU and DSP, as well as some system memory. At the beginning of the advent of Divx encoder, encoder developers used computers with a main frequency of over 400MHz to complete decoding. It can be seen that MP4 requires high computing performance of the chip, and many gorgeous operating interfaces of MP4 also consume a lot of system resources. MP4 is not only a processor for video data and image data. MP4 is still the unity of many digital functions and multimedia functions. Realize formal functions, such as digital companion, video capture, DC, FM, games ... and even some MP4s support multi-line work. Therefore, MP4 chip not only needs high computing power, but also integrates various functions.
Because the production of MP4 core chips requires a high level of technology, MP4 manufacturers are powerless. These cores are generally made by people who use traditional chips, such as Intel, TI and Sigma Designs. Even AMD has introduced a special processing chip for MP4-Au1200. At present, MP4 mainly adopts TI scheme and Wintel's complete software and hardware scheme. Among them, TI (Texas Instruments) is the chip giant of mobile entertainment equipment, while the chip giant of Intel desktop platform, because TI started early, now most MP4s adopt the chip scheme of TI, occupying most market share. Although the hardware has certain specifications and the software system has no unified standard, they are all developed by the manufacturers themselves (mostly Linux), which is also a major reason for the "chaos". At present, most manufacturers adopt TI scheme, mainly digital manufacturers from Aviva, Sony, Toshiba, Europe, America and Japan.
Wintel is a powerful alliance, which has launched a new PMC standard, with Intel's XScale series as the central processor and Microsoft's Windows Portable Media Center as the software system. Both software and hardware have unified standards, which fully reflects Microsoft's ambition to enter the portable media market. Because the whole architecture of Windows Portable Media Center is open, its application software can be extended on the basis of operating system. Wintel's antipathy unified the standards of the industry, and pointed out the direction for the development of MP4 to some extent. At present, there are mainly iRiver, MSI, Samsung and Innovation that support this scheme.
TMS320DM270 chip;
Internal structure of TMS320DM270: It is the core of TMS320DM270. It can be seen that this chip is a very powerful chip, which is mainly composed of three cores: ARM(80MHz), c 54 DSP(90 MHz) and iMX( 180MHz). ARM7 RISC microprocessor is mainly responsible for the management of external interfaces, and C54DSP digital signal processor is responsible for all kinds of audio processing. In addition, the integrated function module and controller make it have other powerful functions, such as photography, card reader, recording, AV-IN/AV-OUT, etc.
TI about MP4 system scheme:
TI's tms320dm270 scheme is one of the most advanced MP4 solutions at present, which has the characteristics of good image quality and good video format compatibility. This scheme was adopted by most MP4s in this cross evaluation. Most internal core architectures of MP4 are coordinated by CPU and DSP. Generally, CPU and DSP are integrated. DSP (Digital Signal Processor) is mainly responsible for video decoding and coding. The central processing unit mainly deals with file management, access, interface and control of peripheral components. In addition, some functional modules need to add special chips, such as DC control module and display control module.
Audio processing
In audio processing, TI mainly adopts TLV320AIC23B encoder developed by itself. It is a high-performance and low-power stereo audio codec chip with built-in headphone output amplifier. The input mode supports MIC and LINE, and the input/output has programmable gain adjustment. AIC23 integrates analog-to-digital conversion (ADC) and digital-to-analog conversion (DAC) circuits, and the output signal-to-noise ratio can reach 90dB and 100dB respectively. It can provide 16/20/24/32 bit sampling in the frequency range of 8 K to 96 K, with pure sound quality, high fidelity, loud treble and clean bass. This audio decoding chip is used in MSI MEGAWVIEW 56 1.
video display
Video display can be output to the outside through NTSC or PAL format, and can also be output to its own LCD screen. At present, MP4 mainly uses LCD screens such as CSTN, TFT and LPTS. For the knowledge about the characteristics and effects of these three screens, please refer to an earlier article in the Pacific: A Comprehensive Explanation of the Portable Media Player MP4 for Literacy Campaign.
access management
At present, the mainstream hard disks MP4 are 1.8 inch hard disks from Hitachi, Fujitsu and Toshiba, and occasionally 2.5 inch notebook hard disks are used. In order to save costs, there are MP4s with small capacity and reduced volume flash memory on the market, but for MP4s, all of them are based on flash memory. Judging from the current technical background and market price, although flash memory has incomparable advantages (stability, low energy consumption and good earthquake resistance), flash memory is not the right way. Since Hitachi released the 0.8-inch micro hard disk last year, it has brought new hope to MP4 in an embarrassing situation.
Power management
As for the power supply, just like the film source, it has always been the dead hole of MP4. The general hard disk MP4 can only support a long video playing life, which is absolutely not enough, especially the MP4 with a built-in lithium battery, which is extremely inconvenient, because the battery life is too short, and it loses the meaning of watching with you. This time, however, MP4 exceeding 10 saw a new hope for battery problems. Some MP4s use removable lithium batteries and AA dry batteries. What's more gratifying is that some can play videos for 8 hours continuously, 1 1 hour.
On MPEG-4 Coding and Format
The encoding format supported by MP4 player can be said to be "chaos in chaos". Except PMC, all software systems are designed by manufacturers, because there is no unified standard for hardware platforms, which is the fundamental reason for the uneven decoding compatibility and stability of MP4 players. In addition, MPEG-4 coding system has produced many formats. Except PMC, the decoding compatibility of MP4 is related to hardware, which greatly increases the difficulty of decoding. There are many video formats, such as AVI, ASF, MPG and WMV, and there are also many coding algorithms: MPEG- 1, MPEG-2 and MPEG-4, which are supported by most MP4 players. There are many derived coding algorithms: DivX, XviD, H.263, MS MPEG-4 3688, Microsoft Video 1, and Microsoft RLE.
Advantages of MP4 player
It can play high-quality video and audio directly, browse pictures and be used as a mobile hard disk and digital bank. Some products also have some very novel and practical functions. For example, AV420 can record video, and it can store the signals of DVD, TV and other devices in the hard disk in MPEG-4 format. The upcoming MP4 player of CIMC Wei Chao Power Company supports PIM management and wireless network functions, which can play more roles after the popularization of wireless environment. Moreover, most MP4 players we see now have professional video functions such as video conversion, and have perfect video input/output ports, so the video files we carry can be played on many occasions. Although this is not of greater practical significance for some users who only use the player on the road, it is very useful for some users who often make video presentations, because MP4 players can be easily connected to output devices such as projectors and televisions. From the point of view of personal use, the biggest advantage of MP4 player is its small size, easy to carry, and it can play videos with you at any time. However, there is more than one product that meets these conditions, and PDA is a competitor. Although it is impossible to directly compare the functions of the two, there is no essential difference between them only from the video playback function of this machine, but the PDA has more functions and the price is relatively cheaper. If you don't often use MP4 player, it's ok to choose PDA instead of MP4.
MP3 player, as its name implies, is a music playing tool that can play MP3 format. MP3 is the abbreviation of MPEG Audio Layer 3. MPEG compression format is a set of standards for images and sounds formulated by moving picture experts group, among which MP3 is a new audio signal compression format standard designed for compressing sound signals. MP3 is a format that uses the third layer audio compression mode in the international standard MPEG to compress sound signals. Chinese is also called "computer network music". The third layer of audio compression in MPEG is much more complicated than the first and second layers of coding, but its sound quality is higher than that of the first and second layers, even comparable to that of CD. The sampling frequency of CD is 44. 1 MHz, and the data volume is 1.4Mbps, while the corresponding MP3 data volume is only 1 12kbps or 128kbps, which is1/kloc-0 of the original data volume. That is to say, a traditional CD can now store 10 times or even more music, but for the human ear, the music effect is no different. MP3 itself is a computing method of compression and decompression, which is used to process high-speed sound information. The sound quality of the sound file it generates is close to that of CD, but the file size is only one twelfth of that of CD. If a CD can store about 12-20 songs in CD format, if it is stored in MP3 format, it can store about 100 songs, which is its charm. The original goal of MP3 is to reduce the file size to facilitate data transmission on the network, and to keep playing MP4 (also called MPEG-4) similar to the original one, which is a kind of MPEG format and a compression method of moving images. Through this compression, smaller files can be used to provide higher image quality, which is one of the most popular video file formats (especially in the network). It is a compression standard for ultra-low bit rate moving images and languages. Used for real-time image transmission with transmission rate lower than 64Mbps. It can not only cover the low frequency band, but also develop to the high frequency band. MP4 provides a broader platform for multimedia data compression, which defines a format and an architecture, rather than a specific algorithm. It can make full use of various multimedia technologies, including some tools and algorithms of compression itself, as well as technologies such as image synthesis and speech synthesis. MP4 has aroused widespread concern since it was put forward. At present, the most popular compression methods of MP4 are DivX and XviD. For DVD programs processed by MP4 technology represented by DivX or XviD, the video and audio quality of images has not been greatly reduced, but the volume has been reduced to a fraction of the original size, so it is very convenient to save the generated files with two ordinary discs with 650MB capacity. If the requirements are lowered a little, a disc can hold movies for more than 100 minutes, and the picture quality at this time is obviously better than that of VCD.
Matters needing attention in purchasing MP4
First of all, from the appearance, MP4 products on the market are mostly rectangular in appearance and have large screens, which is convenient for users to watch movies well. The size and appearance of MP4 and the distribution of keys play a key role in consumers' use. The compact body is easy for you to carry. The design is based on personal preference. If you buy an MP4 that you hate for some reason, I believe you will regret it when you buy it. The distribution of keys is also very particular. The left hand is suitable for operating keys that are not often used, and the right hand is suitable for operating some functions that require strength and must be used during use, so the manufacturer will arrange the key layout reasonably. Bian Xiao hopes that users will not only pay attention to one aspect and ignore other aspects when purchasing MP4. Such as Chaohua, Aiko, Pizza, etc. Their size and operation are acceptable. For example, MP4 of PISA uses ergonomic design principle to make the back concave, which is convenient for hand holding and operation.
Secondly, the host will talk about the screen of MP4. Now the screens on the market are divided into 2.5 inches and 3.5 inches. It's all in 260 thousand colors. Only a few products have insufficient color saturation because of the LCD screen. So be sure to pay attention to the color clarity of its screen when choosing.
Third, whether MP4 depends on the supported format. As we all know, MP4 is called it because it can support professional audio and video playback formats, so this aspect is also the place that consumers need to focus on. If only one audio and video playback format can be supported, it is a bit far-fetched to call this product MP4. But as we all know, the more supported formats, the more convenient it is to watch movies. We also need to know whether many formats of this MP4 need to be converted before we can view it. As we all know, it takes a long time to convert a certain format, which will bring great inconvenience to users. PISA's power cinema, introduced by professionals, can directly play movies in MPEG-4, DVD, VCD and other formats without converting DVD and VCD into MPEG-4. It is equipped with a mini remote control. It also supports AVI, MPG, DAT, VOB and other video formats.
Fourth: playing time. Choosing an MP4 is nothing more than wanting to watch a movie, which usually lasts about 2 hours. Most consumers travel with MP4. If they watch it for a while, the battery will run out and they can't find a place to charge it in time, it will be too depressing. The MP4 broadcast that everyone sees now is basically about 4 hours. But it usually only takes 2-3 hours. At present, the longest playing time on the market is 6 hours, and products such as Aviva and PISA can meet this standard. It should be noted that the detachable lithium battery is more practical, and the battery can be replaced when the battery is used up, but many MP4 batteries are non-detachable, so be sure to ask clearly when buying and try to choose a detachable one. As for the standby time, it is usually 3 ~ 4 hours for video playback and 10 hour for audio playback.
Fifth: the price. High price is an important reason that restricts the maturity of the market. On the one hand, the high price comes from the high production cost, on the other hand, it is caused by the high requirements of manufacturers for product profits-it is precisely because of this problem that a considerable number of products seen in the market are still above 5,000 yuan, resulting in poor market response; At present, Power Cinema in Pisa is the first product to reduce the price to less than 4,000 yuan. I hope to see more and more manufacturers join this camp, so that consumers will no longer be discouraged from MP4, and * * * will promote the development of MP4 market together. Having introduced so much, you probably have a certain understanding of MP4. Many mp4 products have additional functions. Consumers can see which functions are most important to them, polish their eyes and learn more about MP4, which can help you buy satisfactory products with more confidence. It is best to get after-sales warranty before buying.
In addition, the group IDC has many products online, which are cheap and have a good reputation.