Problem description:
How to convert MP4 files? You can play with my MP4.
Analysis:
What is 1 MP4?
At present, many consumers have a vague understanding of MP4, so they simply think that the next generation MP4 of MP3 can play MPEG-4. Later, with the accumulation of knowledge, they have a more systematic understanding. 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.
There are different opinions about the concept of MP4. The picture below shows the author's understanding of MP4, which is both "soft" and "hard" and complicated.
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".
MP3 capable of 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.
2.MP4's Hardware Architecture
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 because the video playback function and the playback of MPEG-4 such as Divx and Xvid require higher processing power of CPU and DSP, and require certain system memory. At the beginning of the advent of Divx encoder, encoder developers used computers with a main frequency above 400MHz to complete decoding. It can be seen that MP4 requires the chip to have high computing performance, and many gorgeous operating interfaces of MP4 will consume a lot of system resources. MP4 is not only the processor of video data and image data, but also the unity of many digital functions and multimedia functions. Need to realize various functions, such as digital companion, video shooting, 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, a powerful alliance, has introduced a new PMC standard. The CPU adopts intel's XScale series, and the software system is Microsoft's Windows portable media center 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 system 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;
From the core of TMS320DM270, we can see 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, C54DSP digital signal processor is responsible for all kinds of audio processing, and iMX engine processes video data and image data. 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. CPU 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.
The scheme is mainly composed of audio processing, video display, access management, power management, video acquisition and TMS320DM270.
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 Liao Xin's 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. Want to know who is right and who is wrong, please see below.
The Core of Microsoft PMC —— Intel XScale PXA255
3. About 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. ......
In streaming media formats, ASF and WMV developed by Microsoft are both encoded by MPEG-4, and some MP4s support ASF or WMV, while RM and RMVB widely circulated on the Internet are not supported by any MP4s. Mpg formats can be MPEG- 1 and MPEG-2 codes and MPEG-4 codes.
Furthermore, it should be noted that MPEG-4 does not determine what extensions must be used. It's just a coding method. Using AVI as extension is a customary practice, which is different from standard avi. At present, mainstream MP4 generally supports avi format encoded by DivX or Xvid, but many other avi formats do not necessarily support it. Finally, format compatibility is also related to the resolution, truth rate and bit rate of video format. An MP4 player supporting DivX can't play the avi of DivX, which is probably related to the above three factors.