Milan video technology exchange meeting sharing

source ：Global Video Tech Meetup：Milan host ：Andrea Fassina The speaker ：Behnam Kakavand, Alexey Malikov Arrangement ： Li Haoyong This conference mainly contains four themes ：WebAssembly As the possibility of network play ; A video DRM How the system works ; Based on real-time edge recording and CMCD KPI Video monitoring panel ;OTT/IPTV Improvement of video content transmission quality . This article will introduce the first and last lecture .

Catalog

• start
• Looking forward to the future ：WebAssembly Or become a way of playing web pages
• OTT/IPTV Improvement of video content transmission quality

start

Meeting by from videodeveloper.io Of Andrea Fassina host . He first reviewed the previous issue （6th Milan Meetup） The content in ： live broadcast 、 Data quality 、 Interactive volume video and intelligent coding , And introduced the other three guests of the meeting ： come from Evolution Of Behnam Kakavand、 come from Akamai Of Luca Moglia、 come from Elecard Of Alexey Malikov.

Looking forward to the future ：WebAssembly Or become a way of playing web pages

This speech （1:37-17:21） The speaker of Behnam Kakavand yes Evolution The company's chief video engineer , from 2010 He began to engage in the video on demand and live broadcast industries in .

Real time video is now at the heart of the industry , To generate and deliver real-time video content , The speakers built their own video platform , For the browser 、 Android provides video content . He USES Websocket To connect Android and browsers , End to end delay at 1.5-3s Inside , And use MSE(Media Source Extensions) To play . And in the Iphone The platform uses HLS, Delay in 3.5-7s Within the scope of . The scenario of this technology is the frequent interaction between users and the streaming end , Delay is critical .

What is? WebAssembly

WebAssembly, That is to say WASM, Is a cross platform binary standard for use in any browser 、 equipment 、 The platform on which the precompiled code runs . Precompiled code means that it is optimized , Low latency code . Compared with JavaScript, with 3-4 Times better performance in terms of running speed . At the same time, you can freely choose its back-end language , Such as C,Rust,Go etc. . This means that you choose from a very large and rich open source library , And add them as new features to your browser application .

Why use WASM player

The speaker chooses WASM To develop their players for the following reasons ：

• It is hoped that the consistency of flow, delay and other service contents can be maintained on the whole platform .
• In order to have more direct access to the decoding function , Gain a global control , Including cache control 、 Packet loss and frame loss control .
• Manage support for various codecs more directly , And the choice of transmission protocol .
• Apple LL-HLS The delay can be controlled at 2s Within the scope of , But that's it. . The speaker's delay goal is 1s.
• WebRTC Limited in encoder , You must use the base configuration file , Resulting in greater quality and bandwidth requirements .

Use the browser's own features

The speaker went on to introduce some features of the browser .HTML5<video> tag Will get the source URL Address and control the whole pipe Video streaming , However, its control range for playing different parts is limited , And on different browsers ,HTML5 There are some differences in the deployment of , More trouble .MSE(Media Source Extension) Will integrate input sources and control almost all parts of playback .

Use custom sections

The speaker introduced the customized part of the player ：WASM and WebGL.WASM Any video codec can be configured 、 You can have customized cache control to achieve low latency playback , You can also choose the transmission protocol freely . because WASM Software codec is used , No hard decoding acceleration support , As a result, the power consumption will be higher . And because the whole larger binary code including encoding and decoding is to be transmitted , Therefore, the transmitted content size will be larger .WASM You can also use various open source codecs , Such as VP9 and AV1, This kind of encoder is not supported on all browsers . and WebGL Can be used for personalized rendering and color gamut space management .

Next, the speaker introduced the workflow of the player . First they use Emscripten Compiled based on C Decoder library , And compile their players based on these libraries .JS Import WASM File and used to synchronize , Input byte cache and read pixel cache , Finally through WebGL Render pixels . He also shows how to compile libav What is used emscripten Configuration of .

WASM Player composition

About WASM Part of the player , As shown in the figure above . The main thread is running on the player JS Front end thread of , It is used for interactive operation for users . In another thread WebSocket Used to operate the transport protocol , And another thread WASM Decoder Used to decode video streams .

The current result

The speaker finally showed their player delay effect , You can see that only 0.9s End to end stability delay , But their current product player delay has 1.8s. In addition, there is a seamless adaptive rate switching function , Can be in iOS,Android And desktop environment .

The speaker's future plans include using shared vector memory , Use WASM SIMD, Off screen desktop and audio category group to further improve performance , It can further optimize battery consumption . In addition, further reducing the size of the player package is also an optimization direction .

OTT/IPTV Improvement of video content transmission quality

This speech （38:26 rise ） My speaker Alexy Malikov yes Elecard The company's engineers .

To improve the service quality , First, you need to monitor the current transmission quality , Therefore, a distributed monitoring scheme is needed . In general, distributed monitoring consists of several parts ： A central server and distributed client applications or hardware . Such a monitoring scheme is needed in the network because OTT/IPTV, Usually （ Including suppliers ） There are multiple clients , Because the quality of the content they provide is often changed during uploading or downloading by satellite , A method is needed to know the final received quality status .

Next, the speaker introduced several real scenarios and corresponding solutions .

Case1: The user's signal is blocked ,TV The picture is stuck during the advertisement

Case1

The speaker installed two detectors , One before transcoding splicer , The other is DVB Before the modulator . There is no problem with the code stream detected in the transcoding part , The latter modulator detects that the parameters of the video stream are different from those of the main video stream . This is a classic mistake , be called “ Video information change event ”.

It can be seen from the monitoring picture shown by him , Because the advertising picture proportion is 16:9, The previously broadcast video content is 4:3, Some user devices cannot directly adapt to this change , This causes the video stream to jam , Affect the viewing experience .

Case2: The video stream cannot be received by the user at all

Case2

In this case , The content distributed network includes satellite links , And detectors have been installed in many places , Including demodulator and transcoder . Through testing, it is found that , The satellite demodulator will not work properly from time to time .

On the detection screen, it can be seen visually that when the demodulation module is not working , There will be no waveform display directly . And the solution is simple ： Directly replace the entire demodulation module .

Case3: The client player stops working

Case3

Here is a large supplier providing business for all areas of the city . The speaker installed a lot of detectors , Included in transcoding distribution , And in CDN Before and after , Even at the regional level CDN Front and rear detectors are installed . In some areas CDN edge , The speaker detected some HLS The broadcast clip is lost , And the download speed is too low to meet the real-time demand .

The regular waveform can be directly seen in the blank of some segments on the monitoring screen , Namely HLS The result of missing fragments .

Case4: The TV channel is inaccessible or severely damaged

Case4

In this scenario , The speaker is before transcoding , Before satellite modulator and after satellite demodulation , End to end detectors are installed , It is observed that there are a large number of data error losses on the transport layer .

The arrival interval of transmitted packets can be seen on the monitoring screen , Change of packet loss rate , Loss of signal occurs at the same time of day . After investigation, he found that this was caused by the signal interference between the two satellites , Finally, the problem is solved by changing the modulation frequency band of the satellite .

Case5: There is no sound at the subscriber

Case5

The speaker is in front of and behind the transcoder on the supplier side and on the client side DVB A detector is set behind the demodulator , On the detector of signal input in front of transcoder , Found the... Of the audio channel PID The loss of .

The audio signal loss can be clearly seen on the monitoring diagram , Without its payload package . Therefore, this problem can be solved quickly after it is returned to the supplier .

Case6: A supplier's picture is stuck

Case6

Here the speaker is in front of and behind the transcoder and CDN After that, the detector is set , The data in front of the transcoder has a big problem .

It is more obvious on the monitoring chart that the transcoder signal can not be used as an input , Caused the picture to freeze , Even after that the signal is restored , Transcoder still can't get back on track . Finally, the transcoder module is directly replaced to solve this problem .

Attach video of the meeting ：

http://mpvideo.qpic.cn/0bc3veaasaaalqamebxtvbqvbkodbguqacia.f10002.mp4?dis_k=4d0100fe20fc264759d75f81606847f6&dis_t=1645152790&vid=wxv_2244374462395793417&format_id=10002&support_redirect=0&mmversion=false