After the analog video signal output by the video signal source is digitized by the video capture card, an important concept involved in digital video and sound transmission is "StreamMedia" (StreamMedia). Speaking of video capture / video capture processing issues, we first need to look at the DirectShow streaming video capture card. At present, Meifit's high-definition audio and video streaming media capture card supports DirectShow standard development and provides a complete secondary development kit SDK. For secondary development of multimedia video applications, it brings great convenience to video capture programming. Is a streaming media architecture on the windows platform. DirectShow provides a high-quality capture and playback mechanism for multimedia streams. In particular, the development of many software (such as video conferencing, videophone, etc.) about streaming video is applied to video capture technology. Video capture and real-time processing are one of the most critical technologies in current video processing systems.
DirectShow simplifies media playback, format conversion, and capture tasks. It is based on the Control Object Model (com). To write a DirectShow application, you must understand com client programming. For most applications, it is not necessary to implement the com object. DirectShow provides the controls you need. (If you want to extend the functionality of DirectShow by writing your own controls, you must implement them as com objects.)
DirectShow uses a standardized architecture. In the DirectShow standard architecture, DirectShow filters interact with controls, diverse devices, local file systems, TV FM and video capture cards, VFW encoders, video display cards (via DirectDraw), and graphics cards. In order to complete the required audio and video stream processing, DirectShow applies DirectDraw and DirectSound technologies. These technologies can efficiently render data images and audio to the user's graphics card and sound card.
Streaming DirectShow technology is mainly software application technology and development technology. Among the DirectShow technology, COM technology also generally calls COM components as Filter, which is generally divided into three categories: Source filter, Transform filter, Transform filter, A rendering filter is used to process streaming data. Filters have input, output pin angles, or both. Filter operates streaming media by reading and writing files, modifying data, and displaying data to output devices. In order to complete the entire task, all Filters must be connected. These three Filters form the Filter graph manager. The source filter, conversion filter, and submission filter complete the data provision, data format conversion (compression encoding, etc.), and data rendering and playback functions. Therefore, in order to achieve video capture under the WIN32 system, we must first construct an appropriate filter chart, and then complete the video capture function through the application program's management of the filter chart.
There are more software for developing DirectShow technology, and more programming languages. In general software development tools (such as VB, VC), you can directly call the MCI control interface under Windows system) functions or media playback controls (WMP, etc.). The relevant file name and other attributes can be set to achieve video capture or playback. With the rapid development of multimedia technology and the application of various compression algorithms in this field, MCI technology is becoming increasingly inadequate. The most obvious is that it does not support variable bit rate compression algorithms. This new media format has become powerless. Subsequently, Microsoft introduced the DirectShow technology based on DirectX in a timely manner. It is also an API (Application Programming Interface). Each DirectX component is the sum of APIs that can be called by users. Through it, applications can directly access the computer. hardware. Supports decoding and playback of media files in various video and audio compression formats from local or network, can capture multimedia streams from the device, and can also process streaming media processed by various compression algorithms. These formats include: MPEG's audio and video standards, Audio and Video Interaction Standard (AVI), WAVE, MIDI, and Advanced Streaming Format ASF. The basic principle of DirectShow is that the multimedia data flows in the filter chart, and the functions are realized through the filters in the filter chart. Finally, the multimedia data is displayed and played back in the submission filter.
At present, domestic research on such projects has been relatively mature, and they are mainly developed with C programming tools. Generally use Filter to complete various functions. Filter is a COM component in the process. The DirectShow SDK provides a set of base class source code, which can greatly reduce the difficulty of developing Filter. DirectShow is located in the application layer. It uses the Filter Graph model to manage the entire data flow processing process; each functional module participating in the data processing is Filter; each Filter is connected in a certain order in the Filter Graph to work together as a "pipeline". The source filter is mainly responsible for obtaining data. The data source can be a file, the Internet, or a capture card in a computer, a digital camera, etc., and then transfer the data downwards; the conversion filter is mainly responsible for the format conversion and transmission of the data; the submission filter is mainly Responsible for the final destination of the data. Finally, the data can be sent to the sound card and graphics card for multimedia presentations, or it can be output to a file for storage.
Like domestic, many foreign software designers also use Filter to implement various functions. DirectShow was originally designed for C applications (you can also use C language). Using Microsoft Visual Basic language, you can access a large subset of the DirectShow API, but VB support is not complete, such as using Microsoft JScript, DirectShow also supports script-based DVD applications. It is also possible to write a DirectShow application using Borland Delphi, however, Microsoft's Software Development Kit (SDK) documentation does not have references on this part.
DirectShow streaming media architecture supports capture based on WDM (Windows Driver Model) and VFW (Video for Windows) digital and analog devices. DirectShow is integrated with other DirectX technologies. It supports multiple formats, including ASF (Advanced System Format), MPEG (Motion Picture Expert Group), AVI (Audio-Video Interleaved), MP3 (MPEG Audio Layer-3), and video capture in WAV sound files DirectShow describes any An application that receives video from hardware. Captured video can be stored on disk or previewed in real time.
With the continuous development of multimedia technology, related software and hardware have emerged endlessly. Now, software and hardware related to multimedia video conferences and video conversations are becoming a hot application that people pay attention to. In these applications, video data acquisition is involved. The traditional VFW video acquisition technology has many limitations and cannot be applied well to various current video systems. Although video frame grabbers using VFW (Video for Windows) drivers are now obsolete, DirectShow still supports them through VFW capture filters. Current video capture cards generally use WDM drivers, so most new video capture devices use WDM (Windows Driver Model) drivers. In the WDM architecture, Microsoft provides a set of hardware-independent drivers, called class drivers, and hardware vendors provide hardware-related mini-drivers. Mini drivers implement any device-related functions. Utilizing the good integration characteristics of DirectShow and WDM video capture card, and adopting the system architecture of component object model, the shortcomings of traditional VFW video capture technology are overcome, and satisfactory results have been achieved in practical applications.
There are many audio and video capture cards for the professional streaming media high-definition field in the Miffy video capture card series products, which are directly compatible with various video applications developed by the Direct Show standard, and can be applied directly without development. M1200 upgrade version of high-definition VGA capture card, M1220 HD DVI / HDMI / VGA capture card, M1320 audio and video streaming capture card, M1230 HD DVI / HDMI capture card, M1620E dual HD DVI / HDMI / VGA capture card Third-party software developed by DIRECT SHOW API, such as fully compatible with Microsoft Direct Show, supports most popular video editing software. Such as Adobe Flash Media Live Encoder, Microsoft Media Encoder, AMCap, VLC Media Player and other video software. It is directly compatible with software on the market such as Beijing Wangdong Video Conferencing, Beijing Century Sunflower Live On Demand Software, VSpeed Video Conferencing, Naga Switcher, Sequoia, LED Control Software LEDShowT9 and Lingxingyu LEDStudio.