| Multimedia technology has been maturely applied in IFE system of modern civil aircrafts because of its vivid audiovisual effects.At present,the product is monopolized by international giants such as Thales and Panasonic,and the price is expensive.Due to the late start of our country’s ”large aircraft” industry,Thales’ IFE system was purchased for the manufacture of domestic C919 aircraft.In order to realize the independent development of China’s civil aircraft industry,based on the cabin entertainment system project of domestic large aircraft undertaken by a civil aircraft avionics research institute,this thesis studied the key technologies of audio and video synchronization in IFE system,aiming at the problems of asynchronous audio and video playback and poor network anti-jitter performance in IFE system.The main work and features are as follows:Firstly,based on the basic theory of audio and video synchronization,the mainstream audio and video synchronization models and synchronization technologies are compared and analyzed.Secondly,because the traditional rate control algorithms encode videos of different complexity with the same initial quantization parameters,resulting in poor image quality after decoding some videos,a rate control algorithm based on improved initial quantization parameters selection is proposed,which improves the video encoding quality and bandwidth usage efficiency.To address the problem of inaccurate network quality estimation,the delay jitter parameter is introduced to calculate the network status index which realizes the accurate evaluation of the network status.Based on this,the network adaptive control algorithm is improved,which provides guarantee for the good quality of video images.By sorting out the technical problems of realizing the audio and video synchronization control and multi-device video synchronization,an audio and video synchronization control scheme based on video frame drop and a multi-device video synchronization strategy based on clock synchronization algorithm are proposed respectively and the application scheme and realization of synchronization strategy in IFE system are offered.On this basis,an audio and video synchronous transmission system based on RTP/RTCP is designed and implemented.The system consists of audio and video encoding and decoding,data encapsulation,buffer zone,clock processing,network feedback,audio and video synchronization control and other functional modules.Finally,a simulation testing platform is built to test and verify the scheme and analyze the results,and an automatic synchronization measurement method based on QR code is proposed.The results show that,compared with before using the synchronization scheme,the average difference in the audio and video asynchronization of the system is controlled within 30 ms from 99.99 ms,and the maximum difference in the frame numbers in multi-device video synchronization is reduced from 4 frames to 1 frame,that is,33.33 ms.In a stable network environment,the system packet loss probability can be maintained at a low level of about3%? if network jitter occurs,the scheme can still achieve good application results when the packet loss probability is not greater than 5%.The audio and video synchronization scheme designed in this paper has been deployed in the independent IFE system and run stably,and has passed the airworthiness certification process of civil in-flight software.The improved rate control mechanism and network flow control algorithm have obvious advantages in ensuring the stability and reliability of streaming media transmission. |
PDF Full Text Request