What is ASF?

1. Overview

ASF The movie ASF is (AdvancedStreamingFormat Advanced Streaming Format) acronym, is Microsoft’s compression technology for real developed a new generation of digital audio streaming online It is Microsoft Windows98 as streaming multimedia file format developed. ASF is at the heart of Microsoft’s WindowsMedia. This is an included audio, video, images, and control commands script data format. WMV and WMA and can be used interchangeably. ASF is an extensible file format for storing multimedia data synchronization. It supports a variety of data transmission networks and protocols simultaneously also proved suitable for local playback. In the clear objectives of ASF is to provide a basis for the multimedia industry-wide interoperability. Each stream file format is composed of one or more media. The file header specifies the contents of the entire file, along with the specific content of the stream. Multimedia data, the file header storage, with particular reference to the media stream number, to indicate the type and purpose. All media streams and provides data synchronized to a common presentation timeline.

ASF ASF is an open standard, it can rely on the support of multiple protocols to transfer data in a variety of network environments. With JPG, as MPG files, ASF file is a file type, but it is designed for synchronous transmission of multimedia data in relation IP network designed, so the information ASF format is particularly suitable for transmission over the IP network. ASF file contents can be both familiar to regular file, it can be a real time by the encoding device to generate a continuous stream of data, the ASF can transmit both people pre-recorded program, the program can also send real-time generated.

ASF for arranging, tissue, to facilitate synchronized multimedia data transmitted over the network. ASF is a data format that can be used to specify a live demonstration. ASF most suitable for transmitting multimedia streams over a network, are also suitable for playing locally. Any compression / decompression algorithm (codec) can be used to encode ASF stream.

WindowsMediaService core is ASF. ASF is a numberAccording to the format, audio, video, image and multimedia information such as a control command script in this format, transmitted in the form of network packets, streaming multimedia content distribution achieved. Wherein the content transmission over the network is called ASFStream. ASF support any compression / decompression encoding, and can use any of the underlying network transmission protocol, with great flexibility.

MicrosoftMediaplayer player is able to play almost all multimedia files, support ASF file format in Internet streaming online, while downloading can be played in real time, without having to listen to downloaded. ASF file local or network playback; scalable media types; component download, scalable media types; prioritized stream; multi-language support, environmental independence; relations between the rich streams and scalability.

2, ASF files created

The movie ASF How to generate ASF file it? Here are two ways to provide software and hardware, for reference:

1, the software will convert MPEG-1 format image files into Microsoft’s new ASF video stream format. Use software tools: SonicFoundryStreamAnywhere and WindowsMediaToolkit. DETAILED DESCRIPTION steps: First, install the ASF WindowsMediaToolkit or compressed version number corresponding driver library copied to Windows / System directory.

Next run software –SonicFoundryStreamAnywhere. Open mpg file. Select “Saveas” (Save As) → select the file you want to save ASF file folder → select “EncodeWindowsMediaFormat” key → set the compression ratio you want to generate the ASF file. If selected, then the equivalent of 250Video compression speed 2MB / minute, the image quality is not very good. Similarly, if the election is equivalent to 4M 512VideoB / min compression rate. In fact, it should be good quality ASF and 320 × 240 in the case where there are 30 frames / sec, it can still image and sound synchronization. Finally, cancel EncodeRealMediaformat option and confirm the completion.

2, using a dedicated video capture card (Ospres-200), by means of “NetshowEcorder3.0” software to convert video recorders, disc players, cameras and other video, audio signal into ASF format. To have a digital format dat, mpg file, the tool can be hero super king 2000 – “vcd turn avi” program, be converted to avi format, and then use the included software to capture card to complete the conversion process ASF. In this specific process is not introduced.

3, ASF file function

The movie data rate ASF ASF file stream may vary between 28.8Kbps to 3Mbps. The user can select an appropriate rate based on their application environment and network conditions to realize VOD demand and live.

1, Demand (VideoOnDemand)
Because the ASF support any compression / decompression encoder may use any of the underlying network transmission protocol, which makes it both at high LAN use, can also be used in low bandwidth dial-up Internet connection environment. Under-on-demand services, interference between users, can control playback on-demand content. In this way the most flexible, but tying up server, network resources.

ASF-demand content are stored on the VOD server, establish VOD site for web publishing, at the same time can be multi-point simultaneous demand the same or different programs, that multiple computers can be in different locations, different time, real-time, interactive on-demand to the same stream ASF file, the user can view and select content on demand via the Internet. Play can be achieved during playback, stop, pause, fast forward, rewind and so on, playback rate 25 frames / s,1 hour of video information in the 300Kb / s acquisition, only 108MB of space, a 640MB CD-ROM can be stored for nearly 6 hours ASF file.

2, Live
under Live service, users can only view the content playback, you can not be controlled. ASF files can be used as a source of media content, real-time multimedia content most suitable for broadcast service. By the camera video capture card, the recorded contents of the microphone input to the computer, the code generation ASF stream, then the signal is transmitted by the machine to a network, a user to watch live content via the web.

The computer may receive the same or a different program channel, broadcast television as a small computer, each computer connected to a network can be received in real time of nine different program channels.

3, distance education
This distance education system ASF files produced by the computer, vod server, the user machine.

the creation of ASF files installed on the computer video capture card, sound card and video cameras for the production of streaming media file; VOD server for streaming media storage and distribution of information; user machine is even ordinary multimedia computer in the Internet, through the web learning. There are instructor-led video files on the web, multimedia courseware, learning executive summary, references, review / practice information questions, and other operations.

4, ASF1.0 introduce

Advanced Streaming Format by Microsoft in 1995 and 1998. Its main purpose is to form as a general storage and streaming. There are two versions of the ASF. A version is ASF2.0, another version of ASF1.0. Here are ASF1.0:

Data type
UINT8, UINT16, UINT32, UINT64- unsigned integer values, 8,16,32, or 64 bits long. In Type GNUC compiler they represent ‘unsigned char’, ‘unsigned short ‘,’ unsigned long ‘and’ 64-bit integer unsigned long long FILETIME- unsigned multiples of 100 nanoseconds

-128 bit GUID value can be generated using special algorithms in any system. The unique algorithm to ensure that any such value (which means two different computers, or even at different times of the time can not produce the same GUID in the same computer). BITMAPINFOHEADER- general structure, describing the image format (compressed).
typedef structure
(
long biSize; // size (the BITMAPINFOHEADER)
long biWidth;
long biHeight;
short biPlanes; // Not used
Short term the biBitCount; [ 123] long-term the biCompression; // image
of the long-term biSizeImage fourcc; // for the image size of the compressed image
// (biCompression0 or 3) may be zero
long biXPelsPerMeter; // not used [ 123] long biYPelsPerMeter; //
biClrUsed long unused; // only available in the color palette image
// number of color palette
) BITMAPINFOHEADER;.. // long biClrImportant; [ 123]

WAVEFORMATEX- common structure, description format (compressed) audio stream

typedef structure (
short wFormatTag; // value, compression format is determined short-term nChannels;
long nSamplesPerSec;
long nAvgBytesPerSec;
short nBlockAlign; // data sample size
short wBitsPerSample;
the cbSize short; // grid sizeType-specific data
) WAVEFORMATEX;
This structure is followed by a series of byte size cbSize.

All of the measured time interval of 100 nanoseconds and is not representative of 64-bit type, or measured in milliseconds and represents the type of 32-bit or 16-bit (per 65.5 seconds).

General Information

ASF1.0 file format by the ‘block’. They are similar to block the AVI format, but also increase the size of their fields. FIG Block 🙁 a)


view of a

Content-type block type described in the block. See the list below referred to as block type GUID. Block length corresponding to the entire block (i.e. data length is only a length minus 24). Other important concepts of the ‘package’. Since the stream format should be, for all practical data, such as compressed video or audio, it is stored in a ‘package’. Unlike the ASF2.0, all packets of a fixed size. Each valid file should contain at least two blocks. They file header and data blocks. Header block contains all the necessary information to start processing actual data, and packet data block contains. Title
1,
File header block
FIG 🙁 ii) FIG bis [ 123] this is a special one, because it contains a data field to other blocks. There may be any number of such large, but we need to know two special types.
2, FIG header object 🙁 iii)

Figure III in the 0x02 flags may mean that the file seekable. The minimum and maximum packet sizes are usually the same. It is not know exactly how to deal with ASF file, assuming its value is not true. 3,
Stream
FIG objects 🙁 IV) FIG four specific data is a data type the meaning can be derived only from the type of flow. Can then field also depends on the value of the audio error concealment type. The second unknown is the value of this goal seems to be absolutely random, but if there are multiple streams in the file, they all hold the same value here. 4, enter a specific

Data
FIG video stream 🙁 V) Figure V Foreign ASF input image formats, usually contains BITMAPINFOHEADER structure, which is 40 bytes long, but it is not a good way, because it may contain some larger scale. 5, a particular data input audio stream 🙁 Figure 6)

FIG six
is equal to the size of the extended format cbSize neat structure of WAVEFORMATEX .

6, the specific data stream audio stream 🙁 — Figure 7)

Figure VII This data is present only if the audio error concealment formula field of the main structure comprising the corresponding GUID. See section ‘audio error concealment’ details in this area. all valid ASF file header contains an object, and a Stream object stream.
FIG 🙁 eight data blocks)


Figure VIII
Pack compressed video and audio data is typically organized into ‘sheet’ or ‘body’ of arbitrary size. When such a person needs to transfer a fixed sized packet, it is impossible to have three opportunities: Size
a) near the frame packet size. This would be acceptable in a storage rack complete package pad size it needs. Ii) frame is greater than the data packet. Then, it needs to ‘broken’ into several fragments, and issue different packets. C) considerably lower than the data packet frame. In this case, it would be a good idea to send more than one frame in the same package. This is called the ‘Group’.
There may be heading a variety of formats, but most of the package film begins with V82_Header 🙁 Figure IX
)

nine
The exact meaning of the
FIG. ,dataI do not know the packet size. It rarely occurs in the ASF stream, when it, it will display the full length of the packet data (from the beginning of the last portion of a packet header). Sometimes ORed with 0x10 or 0x8, but I’ve never seen the package specified non-zero fill scale development of 0x40 and flags. Figure X The most significant bit (0x80) FIG portion 🙁 X)

in the stream number, if a key frame portion contains. Here’s something to be a little bit complicated. Specific areas depending on whether the segment is part of a packet (i.e., the range comprises more than one), or not. This can be deduced from the value of flags, which is itself in some specific areas.
the specific field period, no packets 🙁 Figure XI)
Figure XI
A “fragment offset” is the offset of the segment objects (e.g., video frames ), which contains it. For fragments of a full frame, fragment offset equal to the length of the object and the data length is zero.
“flags” may be 0x01 or 0x08.0x01 means “(part of the plurality of objects) group”, and 0x08 means “no packet (a single object or fragment thereof).” “data length” field is not necessary, if this is the only part of the data packet, as in this case, all remaining data space required, packet (of course, take into account the filling). Therefore, it is only when the current 0x01 bit set package flags.

A “fragment offset” ‘group type ID’ header field size value is determined. Known possible values ​​and the latter is 0x55,0x59 0x5D, which is equivalent to 1, 2 and 4 bytes in size.

subdivision header value “data length” field size is determined. When there are several segments, the lower bit (about 6) contains several parts, means disposed 0x40 bit ‘data length’ field is a 1 byte wide portion, and means disposed 0x80 bit ‘data length, 2-byte wide field portion. Otherwise, the default size of the field is 2 bytes.

Specifically art section, FIG packet 🙁 l)


Figure XII
Such a structure is similar toNo grouping, but it does not have “fragment offset” field because the division and grouping can not be performed simultaneously.
Each part has a field called ‘serial number’. It can be used to re-fragmented objects. Then the object sequence number difference 1 (have a greater jump occurs when ‘sequence number’ field of the packet). Different fragments of the same object having the same serial number and a start time of the same object. Package is usually organized to increase the stamp. It is not clear if it is always the case. Package may be lost, this situation should be handled. 5, related terms
AVIWAVWMAMPCASFWMV

6, References

Slackware: http: //avifile.sourceforge.net/

dret .net: http: //dret.net/

to the top network: http: //www.zdnet.com.cn/