FLV & Flash video Learning Guide

Source: Internet
Author: User
Tags flv file
ArticleDirectory
    • Flash video introduction
    • Flash video creation list
    • Requirements
    • About videos and Web
    • About flash videos
    • Select option
    • Encode Flash video (FLV) files and create these files
    • Capture high-quality videos
    • Optimal Method for encoding on-demand videos
    •  
    • Comparison of transfer options
    • Encode real-time videos
    • Video standards: NTSC and pal
    • Frame Size
    • Frame Rate
    • Pixel aspect ratio
    • Staggered and progressive videos
Flash video introduction

Macromedia Flash video allows you to play the video with the negative effect of Wei Wen Shuo-quko, and blow the mother's horn. Why did you say it became a rare game? Flash video, which includes information about how to create and publish a Flash video.

Flash video creation list

The following steps describe how to create a Flash video and publish it online. The process of creating and publishing an on-demand (pre-recorded) video is different from that of creating and publishing a real-time video.

For information about real-time videos, see broadcast real-time videos.

To create an on-demand Flash video, follow these steps:
    1. Obtain some videos. It can be captured by yourself or by others.
    2. Video Encoding in Flash video (FLV) format. See capture a video and encode it.
    3. Determines the transfer mechanism. See transfer options of Flash videos.
    4. Add the video to your webpage, and then publish the webpage to the Web. See Add a Flash video to a website.

Note:This tutorial applies to flash 8 users. If you are using Flash MX 2004, see the flash video learning guide of previous versions.

Requirements

To complete this tutorial, install the following software and files:

Flash Professional 8
    • Trial
    • Purchase


About videos and Web

The video exactly matches the internet. Video is the most media that reflects our daily visual experience, while Internet is a paradise with no boundaries and interesting content. Therefore, you may expect thousands of compelling websites to integrate videos with data, content, and interactive controls to create a rich experience that surpasses the TV video content.

Unfortunately, the early video content on the Web is usually a rectangle containing the content played on the computer monitor, usually located in a separate pop-up window containing the webpage that generates it. Video images are usually very small and ugly, resulting in poor overall experience.

To address some technical challenges, designers must fully tap into the maximum potential of video content, including the following:

Bandwidth limit

A video is a format that contains a large amount of data. Even a short video clip requires several megabytes of data to be displayed. The development of broadband greatly alleviates this technical challenge. More and more site visitors have the bandwidth required to receive video content through the Web, but the file size is still a challenge for many visitors.

Complexity of web video creation

There is no standard tool set for creating interactions, navigation controls, and integrating videos with other rich media content. Moreover, most video playback clients are not pre-installed on most visitor systems, so many visitors must stop to download plug-ins or applications.ProgramTo view the video.

Lack of excellent integration of videos with other Web Content

In addition to video playback in the rectangular window, most web video formats do not provide rich media functions.

Fortunately, Flash video (which provides video content and context seamlessly in the form that site visitors can use flash player to view) solves these problems.

For video technology information, see video standard technology overview.

About flash videos

Flash video has creative technical advantages, allowing designers to integrate video, Data, graphics, sound and Dynamic Interactive controls to create a fascinating rich experience. Benefits of using flash to provide videos online include:

Widely used

Since Flash video was introduced in 2002, Macromedia Flash Player has become the most widely installed Internet video client. More than 96% of all computers connected to the Internet are running. In addition, Flash Player can run on various platforms and operating systems. The widespread use of Flash Player ensures that most visitors can view Flash videos without downloading other plug-ins. Therefore, you can send videos to more people at low development, testing, and support costs.

Comprehensive creative control

Flash videos can be seamlessly integrated into your website. You can create new "appearances" to customize your type and design unique controls. You can also set the video size and aspect ratio, and the video can be dynamically changed based on the data source.

Rich and interactive context videos

Flash videos can be played quickly and provide a fascinating interactive experience. Because flash only treats flash videos as another media type, you can treat any other object in the SWF file, the lash video is an integral part of the viewing experience, rather than an isolated pop-up window that will interrupt the experience.

The following image shows a complex web page that contains a Flash video synchronized with text and graphics. The overlapping blue dotted line outlines the display area boundary of the SWF file, and the red dotted line outlines the display area boundary of the Flash video (FLV) file as part of the SWF Content. SWF files can contain graphics, text, and client logic (for example, used to create video controls ). It can point to an external FLV file and play it in Flash Player. The FLV file mainly contains audio and video, which are played in the SWF file.

Figure 1.Flash video files played in SWF files

The following is a list of tools and servers that can be used to create and provide a fascinating Flash video experience.

Flash Professional 8Includes the following tools and functions:

  • Flash video import wizard. You only need to select "file"> "import"> "import video" to import the video to flash. The "import video" dialog box guides you to convert a video file to the FLV format and configure the flvplayback component.
  • Flvplayback component. This component can be used to play an external FLV file in a flash video and connect to the Flash Media Server * (formerly known as the Flash Communication Server) video stream. This new video component contains the video playback control, making it easier to customize the video player or set the "appearance" of the video player.
  • New encoding options. You can encode a Flash video in three ways: the Flash video import wizard, the independent flash 8 video encoder, And the Flash video QuickTime export plugin, you can encode the audio and video into the FLV file format when exporting from a third-party video editing application that supports the QuickTime Export program plug-in.
  • Flash Media Server(Formerly known as Flash Communication Server) is a Macromedia Streaming Media Server that processes audio and video of Flash Player 6 or later versions.
  • Flash video stream serviceIt is a cost-effective monthly subscription service provided by a third party. It uses Flash Media Server to provide hosted streaming videos with high performance requirements and world-wide scalability. If you cannot or do not want to install your own Flash Media Server or Flash Communication Server, you can use the hosting service. For more information about the flash video stream service (fvss), see use the flash video stream service to provide high-quality videos *.
  • DreamweaverIncluding the Flash video import mechanism, you can easily put flash videos into webpages, and provide a limited number of custom or "set appearance" Options for video players. Note: You must have an encoded FLV file to use it in Dreamweaver.
  • Flash PlayerUsed to play flash videos and other flash contents.
Select option

Before using flash videos on a site, you must determine the video transmission method. There are two main options: Progressive download or stream video transmission.

Note:You can also embed videos into the flash timeline. However, this is only recommended for very short video clips without audio tracks.

For help deciding which shipper option to use, see the following table. Find your current situation in the left column and view the recommended transfer options. If two options are marked, we recommend that you use either of them.

  Embedded Progressive Stream
The clip length cannot exceed 5 seconds.      
The length of the clip is 5 to 30 seconds.      
The clip length exceeds 30 seconds.      
Expect a small audience      
Expected audience      
Quick Start      
Intellectual Property Protection      
Real-Time Video Stream      
Different Stream Transfer Rates Based on visitor bandwidth      

For more information about transfer options, see transfer options for flash videos.

After selecting the transfer option, select the creation tool: Flash or Dreamweaver.

Importing videos directly to Dreamweaver is an ideal scenario where you want to quickly and easily import videos to your website. In this case, apart from simple video control (playback, stop, pause, fast forward, and fast return) there are no other interaction elements.

If you need to build more interactive experience or a large number of custom video appearances and behaviors, you must use the video feature of Flash 8. You also need to use Flash Professional 8 to encode Flash video (FLV) files.

For more information about the creation options, see Add a Flash video to a website.

Before adding a on-demand (pre-recorded) video to a webpage, you must capture the video and encode it. This includes converting it to Macromedia Flash video (FLV) format.

This section provides information about how to encode On-Demand videos, including background information about how to encode flash videos and how to achieve the best effect when capturing videos.

This section assumes that you already have some videos in non-FLV format. Many leading video editing tools can capture videos directly from digital cameras. For more information about how to capture videos, see capture high-quality videos.

For information about how to convert (encode) Existing videos to FLV format, see the section "encode and create flash video (FLV) files" below.

To capture and publish real-time videos, use Macromedia Flash Player and Macromedia Flash Media Server (formerly known as Flash Communication Server ). For more information, see the broadcast real-time video page in this article.

Encode Flash video (FLV) files and create these files

Flash provides a variety of video encoding solutions that can encode video clips into the FLV format.

Flash video import wizard

The Flash video import wizard allows you to encode a video clip in the Flash video (FLV) format when importing it. However, the "video import" Wizard is also limited, that is, only one video clip can be encoded at a time, and the encoding process takes a long time and requires a lot of computing.

For users who use a large number of video-based content, Flash Professional 8 provides flash 8 video encoder and QuickTime exporter.

Note:Flash Basic 8 only supports video encoding for embedded videos.

Flash 8 Video Encoder

Flash 8 video encoder allows you to process video clips in batches and encode multiple clips at the same time without interrupting the workflow. In addition to video and audio content encoding options, you can use flash 8 video encoder to embed command points into the encoded video clip, and use the cropping and trim controls to edit the video.

For more information, see online help in the Flash 8 video encoder application.

FLV QuickTime export plug-in

If Macromedia Flash Professional 8 and QuickTime 6.1.1 are installed on your computer, you can use the FLV QuickTime export plug-in to export FLV files from the supported video editing applications. Then, these FLV files can be directly imported to flash for use in Flash documents.

The "FLV export" plug-in supports the following video editing applications:

    • Adobe After Effects (Windows and Macintosh)
    • Apple Final Cut Pro (Macintosh)
    • Apple QuickTime Pro (Windows and Macintosh)
    • Avid Xpress DV (Windows and Macintosh)

Using the FLV QuickTime export plug-in to export the FLV file in the Flash 8 video encoder or video editing application can greatly simplify the process of using the FLV file in the flash file. With the "FLV export" plug-in, you can select encoding options for video and audio content during export, including frame rate, bit rate, quality, and other options. You can directly import the FLV file to flash without re-encoding the video after the import.

About on2 VP6 and Sorenson spark video codecs

By default, the Flash video encoder uses the on2 VP6 video decoder to export the encoded video to be played in Flash Player 8, use the Sorenson spark codecs to export the encoded video to be played in Flash Player 7. The decoder is a type of compression/DecompressionAlgorithmIt can control the compression mode of video files during encoding and the decompression mode during playback. When creating Flash content for a video, the preferred video decoder is VP6. VP6 provides the best combination of video quality while maintaining a small file size.

If the Flash content is dynamically loaded with the flash video (using progressive download or Flash Media Server), you can use the VP6 video instead of re-publishing the SWF for Flash Player 8, the premise is that you can use Flash Player 8 to view the content. By transmitting or downloading the VP6 video stream to Flash SWF 6 or 7, and then playing the video with Flash Player 8, you can play the video with Flash Player 8 without creating a new SWF file.

Note:: Only Flash Player 8 supports publishing and playback of VP6 videos at the same time.

Codecs Content (SWF) version (released version) Flash Player version (required for playback)
Sorenson spark 6 6, 7, 8
7 7, 8
On2 VP6 6 8
7 8
8 8
Capture high-quality videos

In addition to the physical attributes of the video, there are many factors that affect the efficacy of the encoder and ultimately affect the user's video playback experience. The following two factors have an important impact on the coding process: Source Quality and frame action.

Source Quality

You only need to press the recording button on the camera to determine the quality of the video source. The following are some basic guidelines for obtaining high-quality source videos and final compression videos of optimal quality.

Use a tripod to reduce Camera shaking.If the camera is unstable, most of the images will shake, which will cause a large number of pixels to change between frames in the video. Camera stability can reduce the number of frames that change between frames, so as to provide you with better quality when the compression rate is high (the data rate is low.

Use good lighting technology.If there is not enough light, even if a high-end camera is placed on the tripod, it cannot generate high-quality images. Low lighting or lighting acquisition filters generate video clutter on the image. This clutter varies with each video frame, making it difficult for the codecs to compress files with high quality. You may need to use or exceed the maximum data rate to compensate for video clutter.

Use the best camera as much as possible.Low-end cameras (especially home cameras recording analog signals on tapes, such as VHS and Hi-8) generate a large number of simulated video clutter. The video quality of digital cameras in movie mode is not very good, and usually produce high-clutter video editing. Even if the camera is placed on a tripod and the light is sufficient, clutter may occur.

You need to adjust your current camera to the best effect.High-end digital cameras, digital Betacam cameras, and 35-mm cameras can generate clear images and produce the optimal compression ratio when the scene is in good light and fixed on a tripod, this allows you to reduce the data rate while maintaining optimal quality. However, you may not be able to obtain professional equipment, Tripod and optimal lighting conditions. Remember: the higher the quality of the video source, the smaller the clutter, and the lower the data rate required to present high-quality playback files.

If possible, always encode uncompressed files.If you convert the pre-Compressed digital video format to the FLV format, the previous encoder generates video clutter. The first compression has executed the encoding algorithm on the video, which has reduced the quality, frame size, and frame rate. It may also introduce some of its own digital human interference or clutter. These clutter will affect the FLV encoding process, so a high data rate may be required to play back high-quality files.

Frame action

Frame action is another factor to consider in the encoding formula. It is the percentage of pixels that change between frames. Moving people or objects, camera effects, or post-production effects will cause pixel changes, as shown below:

    • Move people and objectsIncluding a person walking through the camera, leaves swinging in the wind, a car passing by or close-up of the face.
    • Camera EffectFor example, camera translation, zoom, or handheld operations can cause almost 100% pixel changes between frames.
    • Post-production effectSuch as dissolving, fading, erasing, or complex video effects can cause a large number of pixel changes between frames.

The more actions a video clip has, the more information the encoder needs to compress. If the video clip is relatively static (for example, the video only contains the speaker's header), the pixel changes between frames will not be too large. The video compression program uses a method that first discards frames and then encodes a series of completely uncompressed frames. Unzipped frames (referred to as key frames) are used to calculate and rebuild lost frames during playback.

Optimal Method for encoding on-demand videos

When encoding an on-demand video, you must weigh various factors, including the volume of action described, file size, target bandwidth, frame rate, key frame interval, and pixel size of the video.

When encoding a Flash video, you can specify the value of some factors. This section provides an overview of some of these settings. For more information about other settings, see the technical overview of video standards.

For more information about specific values for various settings, see the Macromedia Developer Center Article best practices for encoding Flash video (best practices for coding flash videos )*. This article provides a recommended setting table *.

The following are some common guidelines for compressing a video into a Flash video so that it can be transmitted over the Internet.

    • Higher target bandwidth (also known as data rate) can obtain more video actions, larger files, better frame rates, and larger pixel sizes.
    • The smaller the video action, the smaller the file size, thus reducing the target bandwidth.
    • As the target bandwidth decreases, the key frame rate also decreases. A low key frame rate (for example, one key frame per six seconds) may cause image softening or blurring, but this reduces bandwidth requirements.
    • When an action increases, the key frame rate, frame rate, and data rate must be increased. You need to send more information to the player for editing with more actions. Since they need to encode the extra uncompressed key frames in the file, it is not suitable for low-bandwidth transmission.
    • When the bandwidth is limited and the frame rate and quality are very important, reduce the frame size.
    • If the video source you encode is directly from the camera, always enable "eliminate interleaved" and set the Flash video encoder to the top field. If the video is staggered, you can select this option to improve the video encoding and playback performance.
Bit Rate

The bit rate is the amount of data transmitted per second. When encoding a Flash video, you must specify the bit rate for encoding. Select a suitable audience bit rate. For example, if most visitors may use a 56 Kbps modem, do not provide videos encoded at 2 Mbps.

Key Frame

Flash video encoding is a series of key frames (the complete frame uncompressed image obtained from the video at a fixed interval). Each frame carries the following information, that is, how to change the pixel of a key frame to generate an incremental frame between the key frame and the next key frame. During playback, the decoder re-creates an incremental frame based on the key frame.

The interval between key frames is the number of incremental frames between key frames. The larger the interval between key frames, the more difficult it is for the decoder to recreate the lost frames. In addition, if the key frame interval is too large, there may be insufficient data rates to compress and transmit data bits. Therefore, if there is a large interval between key frames for video editing with many operations, the image quality will be poor.

For flash videos, key frames are especially important if your demo method provides the search or cleaning function so that users can take fast forward operations during playback. (To search for and clean up videos, you must use the Flash Media Server or Flash video stream service to stream the videos .)

Multiple options are available for transferring Macromedia Flash videos on the site. You must select a transfer option before adding the Flash video to the site.

Comparison of transfer options

The following table compares the features of Flash video transmission technology:

  Embedded Video Progressive FLV Stream FLV
Encoding By default, the "Flash video import" Wizard encodes the video that uses the VP6 video codecs for Flash Player 8, and encodes the video that uses the Sorenson spark codecs, for Flash Player 7. You can also import the FLV file (which has been encoded elsewhere) and place it on the flash timeline (without re-encoding ). These files can be encoded when you export FLV files from a variety of professional editing and encoding applications through the "Flash video import" wizard in the FLV QuickTime export plug-in and Flash Professional 8; you can also use independent Flash video encoding to encode these files. Note: All these options require Flash Professional 8. Same as progressive FLV. In addition, the bandwidth detection function in streaming can detect client connections and input videos encoded accordingly. Real-time video input can be captured through the Client Network Camera or digital camera (DV), and real-time Encoding variables can be controlled programmatically.
File Size SWF files include video streams, audio streams, and Flash interfaces. Therefore, a file is extremely large. SWF files can be loaded to each other, allowing you to split a single video clip into multiple files. Save the SWF and FLV files respectively to reduce the size of the SWF file. Same as progressive FLV.
Timeline access After a video is embedded into the flash timeline, the video appears on a single key frame and can be processed like any other object on the stage. It is suitable for creating interactions based on a single video key frame. The video is only played back during running. A single key frame is invisible on the flash stage. Same as progressive FLV.
Release Each time Flash content is published or tested, the entire video file is re-published. To change the video file, manually import the file to the Flash timeline. FLV files are referenced only at runtime. The publishing operation does not need to directly reference the video file, so it is much faster than the embedded video method. You can update or modify the FLV file without changing the SWF file of the project. Same as progressive FLV. FLV can be dynamically extracted from virtual locations (such as San or Flash video stream service CDN.
Frame Rate The video frame rate must be the same as the SWF frame rate. The frame rate of the FLV video file can be different from that of the SWF file, so that the video and other Flash content have different timing. Same as progressive FLV. Real-time video capture can be programmed to control the frame rate.
Access to ActionScript You can control the playback of SWF Content on the flash timeline to achieve video playback and control. Flash MX 2004 and flash 8 contain multiple actions for controlling video and audio playback. You can use the netstream command to "LOAD", "play", "pause", and "Search" multiple external FLV files. Same as progressive FLV. You can also use server-side ActionScript to provide other functions, such as stream synchronization, server-side playback list, and smart Transmission Based on Client connection speed adjustment.
Components No video-specific components. You can use media components (only for Flash MX Professional 2004) or flvplayback components (only for Flash Professional 8) set and display external FLV files and transfer controls ("play", "pause", and "Search "). The flvplayback component (applicable only to Flash Professional 8) can be used to transmit video streams from Flash Media Server or Flash video stream service. In addition, you can use the Flash Media Server Communication component to transmit real-time and multi-direction video streams.
Web Transfer Unless you embed a SWF file into a video clip, the file will be downloaded progressively. For progressive download, you must download the entire video to the client and load it To the memory before the video can be played back. Incrementally download and cache FLV files, and then play back the files from the local disk. The entire video clip does not need to match the memory size. Transfer FLV file streams from the Flash Media Server, play these files on the client's computer, and then use the method of transmitting and playing together to discard these files in the memory.
Performance The limit for synchronizing audio and video is about 120 seconds after the video is played. The total file duration is limited by the available memory on the playback system. Using larger and longer videos and reliable audio synchronization improves the performance of embedded SWF videos. Provides the best image quality, which is limited only by the size of available hard drive space on the playback system. Best Performance is provided from the perspective of web transmission, and best bit rate transmission is provided as much as possible based on the needs of most customers. Image quality is limited by the bit rate that can be transmitted in real time.
Usage Shorter video clips (less than 320x240) with a low frame rate (12 FPS) (less than 1 minute ). Large (720x480 and larger) video clips with a higher Frame Rate (up to 30 FPS. A large number of videos, extremely long video clips, and real-time and multi-direction stream transmission (such as online photo server chat and real-time event broadcast ).
Compatibility Flash Player 6 and later (on2 VP6 codecs require Flash Player 8 or later .) Flash Player 7 for Sorenson squeeze decoder, Flash Player 8 for on2 VP6 Decoder Flash Player 6 and later

 

Encode real-time videos

For real-time Flash video streams, real-time video sources can come from any camera connected to a computer. It can be a network photo camera connected to the USB port of a portable computer, or a digital camera connected to a high-end video capture card.

Real-time videos can only be stream videos. Other options that can be used for on-demand videos (embedded videos and progressive download of FLV files) cannot be used for real-time videos.

Flash Player 6 and later include an audio and video encoder used to directly capture audio and video from any camera or microphone connected to the computer. Run a specific type of SWF file (also known as a broadcast application) on the computer connected to the camera ). The broadcast application contains all the settings required for real-time video encoding. Many of these settings are conceptually the same as those described in the On-Demand section of this document (such as bit rate and key frame.

Capture cards and other real-time video encoding hardware Improve the Quality of real-time videos by sending better video signals to broadcast applications and moving most of the encoding processing in Flash Player to hardware. However, such hardware is not necessary for basic real-time video streams.

The broadcast application sends real-time videos to the Flash Media Server or to the Flash video stream service server, which resends the real-time videos to be viewed by anyone connected to the stream.

The real-time video function in Flash Media Server includes audio push, recording, and record appending. In addition to real-time video streams, Flash Media Server also allows you to provide video chat, video information, network broadcast, video conferencing, and frozen animation capturing. For information on using real-time videos for Advanced Streaming functions, visit the Flash Communication Server homepage on macromedia.com.

Details about how to create a broadcast application are beyond the scope of this document. However, Flash Media Server includes multiple application programs and component examples for capturing and broadcasting real-time videos. For more information about the settings you want to use, see the Macromedia Developer Center Article encoding best practices for live video (best practices for real-time video encoding )*.

In addition to broadcast applications, you must create a web page that allows visitors to view broadcasts. The page creation process is similar to the process of creating any page for viewing video streams. For more information, see Add a Flash video to a website.

This appendix describes the basic concepts and usage of video parameters and standards.

Video standards: NTSC and pal

The video displayed on the TV screen follows the standard established when the first color TV was introduced in 1950s. The mainstream formats currently used are NTSC and pal ). In general, NTSC is the standard used in the United States and Japan, while pal is the standard used in Europe, Australia, the Middle East and Asia.

These two video standards are not optimal for display on a computer display; each will expose different problems when you try to optimize videos for Web Transfer:

    • Frame Size:NTSC and PAL have different image sizes, both of which are different from the available image sizes of computer monitors.
    • Frame Rate:NTSC and PAL have different image display frames, both of which are different from those used by computer monitors.
    • Pixel aspect ratio:NTSC and PAL use the same pixel aspect ratio (d1 aspect ratio, which is essentially a rectangle), but this aspect ratio is different from the aspect ratio used by computer monitors (this aspect ratio is a square ).
    • Display:NTSC and PAL are composed of two separate "staggered" fields, while computer displays "progressive" images.

The following table summarizes these differences:

  Image Size Frame Rate Aspect Ratio Display
NTSC 720x480 29.97 D1 Staggered
Pal 720x576 25 D1 Staggered
Computer Change
(Much larger)
-- Square Progressive
Frame Size

Traditional TV screens consist of horizontal lines, while computer displays consist of a series of horizontal and vertical pixels. The standard row resolution of ntsc TV is 525 rows, and the standard row resolution of PAL is 576 rows. Most modern computer displays have a much higher vertical resolution (in pixels), such as 768 or 1024, which requires a vertical extension during playback to fill the display.

For NTSC video images, the SMPTE 259 m professional standard specifies that 525 rows are represented as 720x486, that is, 720 horizontal pixels x 486 vertical pixels. The default video size is usually D1. Using the latest video capture card to capture a lens from a professional betasp or digital Betacam source will generate a D1 frame. However, capturing a lens from a DV (Digital Video) Source generates 720x480 frames. The difference between the D1 specification and the DV specification is only 6 vertical pixels. Many compression algorithms (including DV compression) are suitable for Pixel sizes that are multiples of 16. By deleting 6 pixels from the D1 resolution, the DV format achieves a 16-fold local resolution.

For PAL video images, no matter which video source is used, the frame is always 720x576 pixels. Since the vertical resolution 576 of PAL is a multiple of 16, you do not need to change DV compression.

Frame Rate

Video is essentially a sequence of images that flash continuously on the screen, and can produce animated visual effects. The number of frames displayed per second is called the frame rate, which is calculated based on the number of frames per second (FPS. The higher the frame rate, the more frames per second used to display the image sequence, and the smoother the animation effect. However, the cost is that a higher frame rate requires more data to display the video, which requires more bandwidth.

NTSC videos are generally considered to run at 30 FPS, and PAL videos run at 25 FPS. In fact, NTSC runs at 29.97 FPS. The reason for using an odd frame rate is traced back to the conversion from a black and white TV to a color TV signal. The latter chooses a 29.97 FPS frame rate to ensure backward compatibility with the existing TV. Although there are still 30 frames, they run 0.1% slower than the actual time, resulting in a frame rate of 29.97 FPS.

In most cases, the frame rate can be adjusted to 30 FPS, 15 FPS, 10 FPS, or 6 FPS. When the video length exceeds 10 minutes, if the frame rate of 29.97 FPS is not followed, the frame rate (for example, half of 29.97 FPS, that is, 14.98 FPS) is reduced by means of accurate average division ), the audio is obviously not synchronized with the video.

Pixel aspect ratio

D1/dv ntsc and PAL specifications specify non-square pixels (usually known as the D1 aspect ratio), while the computer display pixels are square. D1 pixels are short in the vertical direction. Therefore, when you view the D1 video image on a computer display, the image is squashed vertically-to make the actors appear shorter. When the image is displayed on a broadcast display, the pixel width is greater than the height and displayed normally, as shown in.

Figure 3.The left image is displayed on the video display, and the right image is displayed on the computer display. Note: The image is compressed vertically on the computer monitor, but normally displayed on the video monitor.

Therefore, you must adjust the aspect ratio by scaling the video image suitable for display on a computer display to a valid aspect ratio of 4-3. For NTSC, the complete square pixel resolution is 720x540 (vertical compensation). For pal, the resolution is 768X572 (horizontal compensation ). The final video display resolutions commonly used on the Internet include 640x480, 512x384, 320x240, and 160x120.

Staggered and progressive videos

A video image consists of two staggered fields, which are combined to form a frame. This method was introduced when the TV was invented. Due to technical limitations, it was impossible to "gradually" Draw on the display without obvious visual jitter (from top to bottom) complete frame; when the image is displayed, it is as if it has been erased on the screen. The human interference is eliminated by dividing the image into two fields (parts) and displaying them one by one. This old technology has been a huge obstacle in the digital video and computer era, and now it has gone from the new video standard of high definition TV (progressive video standard, that is, drawing images from top to bottom at a time). A set of straight lines is called a field. Two games are called playing and playing, or playing 1 and playing 2. They can also be called odd and even games, top and bottom games. Unfortunately, there is no standard naming method yet.

Figure 4.It displays two fields and the frames generated by these two fields in an interactive manner:

For actual video lenses, the two staggered fields are usually very similar to each other, and visible human interference is not displayed when viewing video frames on a computer monitor. However, for video lenses that contain rapidly changing high-speed animated materials (such as the movements of cameras or characters in frames, there will be very obvious field interference, resulting in poor image quality. This is because the two time periods are merged into one frame.

Therefore, to display a clear video on a computer display, you must cancel the video frame crossover by eliminating a certain field. If you discard half of the information of each frame, the remaining information will be doubled and staggered. For NTSC, 30 frames are generated, and each frame is composed of 30 different time points.

Figure 5.The left side of the image is a staggered frame; on the right side of the image, a field has been eliminated to generate a "de-staggered" frame.

The modern digital TV video standard eliminates the crossover and is recommended to use progressive scan display technology. Progressive Scanning cameras can usually switch from progressive scanning back to staggered videos, and most of these cameras have a variety of frame frequencies with and without interleaved frames. Typical frame frequencies are described as 60 p (60 FPS progressive), 30i (30 FPS staggered), 30 p (30 FPS progressive), and 24 p (24 FPS progressive ). When you use progressive images, you do not need to uninterlace the lenses before deploying them to the Web.

 

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