From the developer's point of view to explain the online video of the various problems

This article from the developer's point of view to everyone in the popular language to explain the audio and video playback problems.

1. Why is 1080P video played on a video site sometimes not particularly clear?

1080P represents the video resolution is 1920x1080, for the image, the higher the resolution, the higher the definition, but video is different, video is composed of multi-frame images, in order to reduce storage space, easy to spread, the image in the video is a certain algorithm compression, and compression will inevitably lead to distortion.

In the video compression algorithm, there is a measure of the compression ratio of the parameters, called: the bitrate. It represents a second of video data size, for example: 10mb/s, representing 1 seconds of video data with 10M bit, for 1080P video in YUV422 format, a frame image is 1920x1080x2x8/1024/1024 = 31.64Mbit, 1 seconds 30 Frame image, then there is a 949.2mb/s, it can be seen that the large amount of data, not compressed at all cannot be transmitted online, therefore, in summary, as a conclusion:

Do not think that 1080P video must be high-definition, clarity and video bitrate closely related to 1080P video, Blu-ray video bitrate is 20mb/s, the general download video bitrate is mostly 10mb/s, some ipcamera/drone's bitrate is 2~8mb/s, And a lot of video site rate is even lower than 5m/s, in fact, sometimes not as high as the rate of 720P clear ~

Why the rate of compression to so small, because now the family bandwidth is generally not high enough to see how much bandwidth your home knows.

2. Why do the "jumping" and "flower screen" phenomena occur during the video playback?

The "jumping" and "flower screen" phenomena are mostly caused by the loss of "critical data" due to bad signal during network transmission, what is "critical data"? For video, it is "keyframe"/"Reference frame", which is explained further below.

As mentioned above, video in the network before the need to compress, and simple to explain the core idea of video compression is: Every 10~50 frame to take a picture of the video as "key Frame", and subsequent frames of the image due to time/space redundancy and correlation, we only need to record its and key frame "difference" information can be, In this way, video files can save space by not having to keep all the full image data of each frame.

Thus, if lost "key frame", then the next few frames of the image will not be properly decoded, resulting in a "flower screen" phenomenon.

From the technical point of view, how to solve the "flower screen" phenomenon? --when we are in the process of video transmission, we can skip the subsequent non-"keyframes" after we find the dropped frames through the frame sequence, until we encounter the next keyframe and then feed the decoding. This can really solve the "flower screen" phenomenon, but because of jumping a lot of frames, so there will be a video image of the discontinuity ("jumping" phenomenon).

3. What is the principle of the bottom sowing of thunder?

The side and bottom broadcast and the local file playback is almost the same, except that the file data is not local, before the player plays to the specified location, the background thread to download the required data in advance.

"Side of the broadcast" is really just like the "download tool" to mention this concept, we are in many other video sites to watch online video, in fact, it is also the side of the download side play, but the download of the data cached in the directory you do not know, the cache directory can be found by the following methods:

View files, settings, general, Internet Options, settings, IE browser, open

Of course, the side of the Thunder and other online sites may be different from the point is that it will be in parallel to speed up video data download speed.

4. Summary

A few questions about online video playback are explained here, have any questions or suggestions welcome message or letter [email protected] exchange, or follow my Sina Weibo @ lu _ June or scan the following QR code follow my public number to get the latest articles and information.

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From the developer's point of view to explain the online video of the various problems