Sorenson spark video codecs

Introduction

　　Sorenson sparkIs flash
The built-in motion video codecs of MX allow us to add video content to Flash MX. Spark is a high-quality video encoding/decoder that can significantly reduce bandwidth requirements while improving video quality. Previously, flash can only use continuous bitmap images to simulate videos. After spark is included
MX has greatly improved the video support capability.

Edit the principles of this section

Spark video codecs are composed of encoders and decoder. The encoder is used to compress the video content. The decoder is used to decompress the compressed content. Decoder included in Flash
In the MX player.

There are two types of applications and digital media compression: spatial and temporal. Time Compression distinguishes between frames and stores only different parts of frames. This allows you to describe the current frame based on the difference from the previous frame. The unchanged area (that is, the same part between frames) only needs to simply repeat the previous frame. Time-Compressed Frames are often called interframes. Time compression is a type of inter-frame compression.

Space compression is used to compress a single frame of data, regardless of the surrounding frame. Space compression can be lossless compression (data in the image is not discarded) or lossy compression (some data is discarded selectively ). Space compression frames are often called inner frames. Space compression is a type of intra-frame compression.

Sorenson spark is an inter-frame codecs. Sorenson
Spark's efficient inter-frame compression is different from other compression technologies. Compared with other codecs, it requires a low data rate to produce high-quality videos. Many other codecs adopt intra-frame compression. For example, JPEG is an intra-frame compression decoder.

However, the inter-frame compression codecs also adopt the intra-frame compression technology. In this case, the inner frame is used as the reference frame (Key Frame) of the Inter-frame ).^{[1] encoding always starts from a key frame, and each key frame becomes the primary reference frame of the next frame. If the next frame is significantly different from the previous one, the decoder compresses it into a new key frame.}

How to compress a video depends largely on the video content. The compression of a head video with only a talk action is very different from that of a football match video. To achieve the best video compression effect, you should pay attention to the following issues when using Sorenson spark to create a Flash MX video:

1. Strive for simplicity. Avoid detailed conversion whenever possible, because the detailed conversion cannot be well compressed, it will lead to the final "obesity" of the compressed video ". Hard cropping usually has the best effect, or quickly fades in and out. It looks cool to zoom in the lens, flip the page, and fly out of the screen after several laps. However, the compression effect is poor and should be avoided as much as possible.

2. Understand the user's data transmission speed. When transmitting videos over the internet, you should generate files at a lower internal network data transmission speed. Users with quick connection can watch your animation without waiting, but users with dialing need to wait for file download. In this case, it is best to generate a short clip to keep the download time within the limits that dial-up users can tolerate.

3. select an appropriate playback speed. The frame speed indicates the playback speed, expressed by the number of frames played per second. If the data transmission speed is high, a low frame rate can improve the playback performance of low-end users.

4. Select the frame size that suits the data transmission speed. The frame size has an important impact on high-quality videos generated by Flash MX animation. Increasing the frame size reduces the video quality at a given data transmission speed (connection speed. When selecting a frame size, you must also consider the frame rate and the connected device. If the moden connection is used, the commonly used frame size is 160x120; 192x144; 320x240.

5. Understand the download process. You should know how long it takes to download your video. When downloading a video, you should display other content to "mask" the download of the video. For short video clips, you can use the following formula to calculate the pause time:

Pause Time = download time-Playback time + playback time × 10%

For example, if the length of your video clip is 30 seconds and the download time is 1 minute, a pause of 33 seconds (60-30 + 30 x 10%) is required ).

6. Use a video without noise. The higher the quality of the original video file, the better the final animation quality. Although the frame rate and size of Internet videos are usually smaller than what you see on TV, computer monitors have better color fidelity, saturation, clarity, and resolution than normal TVs. Even in a small window, digital video image quality is more important than standard analog television. Signal Noise that TV seldom notices is unacceptable on computers. After capturing a video, you should remove the noise and crossover. Audio should also use files without noise like videos.