Distributed video coding (DVC) has attracted the significant attention of many relevant international standardization committees and experts ever since the emergence of distributed source coding (DSC). DSC is a new class of source coding approaches based on the Slepian-Wolf theorem and the Wyner-Ziv (WZ) theorem. Owing to its characteristic of slight encoding and high error robustness

DVC is a good way to meet the demands of the new video business

which requires low-power consumption and low complexity

such as video chat

unmanned aerial wireless monitoring

and so on. However

the bit error ratio of the wireless channel is higher than the wired channel because of the impact of the channel attenuation

multipath interference

frequency band mutual interference

and so on. In the DVC system

video source is interleaved with key frames and WZ frames

and the side information regarded as the noise version of the current WZ frame is generated by the motion estimation and compensation algorithm of the adjacent key frames. Therefore

the key frames

regardless of their ability to correctly decode and transmit

would affect the compression efficiency and rate distortion of the whole system. However

the robustness of the key frames that use traditional intra-frame coding is far lower than that of the WZ frames

which are based on channel coding. For the robustness and transmission of key frames in the heterogeneous network

this paper presents a quality scalable protection solution for the key frames in wavelet domain DVC. At the encoder side

the key frames are encoded by the traditional HEVC/H.265 (High Efficiency Video Coding) intra-frame coding and Wyner-Ziv coding based wavelet domain simultaneously. The HEVC bitstreams are transmitted to the wireless channel. The information bits are directly discarded for the WZ bistreams

and the generated parity bits are stored in buffer. To make the bit rate of the system adapt to different network conditions

different layers of low-frequency and high-frequency bands of the wavelet decomposition image can be combined into different enhanced layers. Initially

the decoder determines whether the HEVC bitstreams of the key frames are lost or not. If there is no error

the HEVC bitstreams are decoded to reconstruct directly

and the WZ parity bits in buffer will be deleted. On the contrary

the error concealment technique will be used to reconstruct a video frame of the received HEVC bitsreams. In addition

the reconstructed frame is accepted as the side information of the current key frame

and the decoder will request the WZ data of different enhancement layer according to the different channel environment. Moreover

the original frame and its corresponding side information roughly obey the Laplace distribution in the DVC system. Therefore

the real practice is to use the forward reference frame and side information to obtain the virtual noise model of the current frame because the decoder cannot obtain accurate original information. However

if the channel condition is limited and there are simultaneous errors in the key frames

then it is impossible to send the parity data of all enhancement layers. As a result

the quality of the reconstructed forward reference frame may be relatively poor and the estimation of the virtual noise model may have a large gap compared with the practical situation. Therefore

this paper improves the virtual noise model of the error key frames because of the similarity of the virtual noise model of the same layer in the wavelet decomposition image. With the decoded bands of the first enhancement layer and its corresponding side information

the more accord actual virtual noise model of the second and the third enhancement layer could be obtained. To validate the effectiveness of the proposed scheme

the luminance of three video sequences with different motion characteristics are simulated

including the

and sequences. The rate-distortion performance over packet loss channels with different random packet loss ratio[i.e.

packet loss rate(PLR)

PLR=(1%

5%

10%

20%)] is evaluated. Experiments results show that in comparison with the traditional error concealment method

the proposed scheme can effectively improve the rate-distortion performance of the reconstructed video image under different channel conditions. Specifically

if only the parity data of the first enhancement layer are transmitted and the loss rate of key frames is 5%

the peak signal-to-noise ratio (PSNR) of the reconstructed video can be improved to about 25 dB. If the parity data of the second enhancement layer continue to be transmitted

the PSNR of the reconstructed video can also be increased from 0.51.6 dB. If all parity data of the three enhancement layers are transmitted

the decoded video can basically achieve the same quality of the key frames without errors. When the data loss ratio is relatively high

such as 20%

the quality of the reconstructed video by typical error concealment method nearly cannot meet the basic requirements. However

with the parity data of the first enhancement layer transmitted

the PSNR could be improved about 4.58.3 dB in the proposed scheme. If the parity data of the second enhancement layer continues to be transmitted

the PSNR could be also increased from 2.74.1 dB

if all parity data of the three enhancement layers are transmitted

the PSNR can also be increased from 3.7 4.6 dB. In general

the different reconstructed video quality could be obtained with the transmission of the different enhancement layers. Experimental results have indicated that the proposed error protection scheme for key frames in wavelet domain DVC can improve the robustness of key frames. The proposed framework can also improve the rate-distortion performance for different channel environments and requirements. However

the proposed scheme is based on the feedback channel

which causes some delay during decoding. Therefore

the rate estimation in the encoder side can be the next direction of research.