ISSN 1843-6188 Scientific Bulletin of the Electrical Engineering Faculty – Year 15 No.1 (29) OBJECTIVE VIDEO QUALITY ASSESMENT: USING H.264 AND H.265 CODECS FOR 4K TRANSMISSIONS NICOLETA ANGELESCU Department of Electronics, Telecommunications and Energetics, Valahia University of Targoviste E-mail: [email protected] Abstract. H.265 codecs has attracted a lot of attention solution can be applied only to MPEG 2 video files to for transmission of digital video content with 4k reduce storage space. In [5], the H.265 and H.264 codecs resolution (3840x2160 pixels), since offers necessary are evaluated on video quality for 4k resolution. The bandwidths saving in comparison with H.264 codec. We authors use three objective quality metrics for evaluation. compare both codecs using three objective video quality The authors conclude that H.265 codec offer the best metrics on five standard 4k video test sequences for improvement comparing to H.264 codec for low bit-rate. digital TV transmissions using both codecs. In [6], a solution to reduce bit rate for MPEG 2 and H.264 transmission is proposed. The base layer at MPEG Keywords: H.264, HECV, VQM, SSIM, objective video 2 standard resolution is multiplexed with the enhanced quality layer (which is the difference between scaled MPEG 2 video content and original high resolution video captured) compressed with H.264 codec and transmitted to user 1. INTRODUCTION destination. The same solution can be applied for H.264 and H.265 content. The users with receivers which Nowadays, the majority of video content is stored in support Full HD resolution view the 4K content scaled lossy compressed form. The optimization in processors and compressed with H.264 codec. In case of receiver architecture, in special the improvement of mobile which support 4k resolution and has H.265 codec graphics chipsets has leads to large adoption of H.264 support, at user destination, the 4K content is obtained by codec for video compression and transmission. The resizing Full HD image to 4K resolution and adding the H.264 compression codec improve quality in comparison enhanced layer compressed with H.265. In this paper we with MPEG-2 codec. The increasing number of digital analyze the variation of quality for H.265 codec, in order TV televisions introduces bandwidth problems, because to recommend the bit rate necessary for enhanced layer. digital TV standards offer a limited bandwidth to cable The content of paper is as follow. The details of operators. In Europe, the EBU (European Broadcast experiments and description of tools used and the main Union) has proposed DVB (Digital Video Broadcasting) compression parameters for H.264 and H.265 codecs standards for digital television transmission [1]. For used in experiments are presented in experimental results digital satellite, terrestrial, mobile and cable transmission, section. Finally, in last section the conclusions are drawn. the available bandwidth depends the parameters of modulation selected. In the case of mobile and satellite 2. H.264 AND H.265 CODECS video transmission, the available bandwidth is more limited and the apparition of television with support for The most used video codec for video storage, digital TV 4K resolution requires an increasing bit rate for transmission and video streaming on Internet is H.264. broadcasting. Because H.264 [2] codec has been most The main discrete GPU and CPU-GPU components also used for Full HD transmission, the H.265 or HVEC (High include support for H.264 hardware video decoding up to Efficiency Encoding Video) codec has been developed 1920x1080 resolutions. The H.264 standard defines for improvement of compression rate and image several profiles for compression with specific encoding resolutions increasing [3]. At same bit rate, the H.265 parameters. The higher profile is selected for codec offers a better image quality, at the price of increasing of calculus complexity. The gain in bandwidth compression, the higher demand for computing resources savings depends by profile and bit rate chosen. Because is required for decoding. The necessary bit rate for the 4k the satellite and cable operators aim to broadcast more resolutions is obtained using the increasing encoding channels to subscribers, the bit rate must be reduced due profile number. The maximum profile number for H.264 to increasing the numbers of channels. The result is the is 5.2. The H.265 increases profile number for encoding lowering of video quality, because a double lossy up to 6.1. The best results in compression rate and video compression is applied. The first lossy compression begin quality are obtained for 6.1, but the encoding times are when the television signal is acquired from satellite by large. Both codec offers CBR (Constant Bit Rate) and operator, then to reduce bit rate in order to pack more VBR (Variable Bit Rate) options for encoding. The channels to subscribers, the channel is recompressed to a maximum resolution of video content supported by H.265 lower bit rate. In the case of large display size, the codec is 8192x4230 along with 4:4:2 and 4:4:4 YUV experience is unpleasant for subscriber in the case of chroma sampling formats. In order to reduce the scenes with more details or high motions. In [4] the decoding time, H.265 codec replace 16x16 pixels effect of transcoding MPEG-2 video to H.265 is macroblocks with coding tree unit (CTU). analyzed. The bit-rate saving is more 50%, but the 5 Scientific Bulletin of the Electrical Engineering Faculty – Year 15 No.1 (29) ISSN 1843-6188 The motion compensation and motion vector predictor to change codec used for decoding video stream by are also improved in new codec. change DirectShow filter. In this case it is possible to evaluate the quality of codec at decompression. The 3. EXPERIMENTAL RESULTS program evaluates the selected metric on a frame-by- frame basis and exports the results in an Excel type file Five test video sequences were used from [7] (Figure 1). with csv (comma separate values) extension. The average The sequences were transformed from sgi format to yuv value for all frames is computed in Matlab for all YUV format using sgi2yuv software [8]. The YUV chroma columns from csv file. The experimental plot results obtained for PSNR, SSIM and VQM metrics are shown format was 4:2:0 8 bits and initially frame rate was 50 in Figure 2, Figure 3 and Figure 4. We observe from frames per seconds, progressive mode. Because all HD experimental results an increasing in quality around 1 dB transmissions in PAL system has 25p or 50i, the content from 12 Mbps to 16 Mbps. The minimum variation is was transformed from YUV to AVI uncompressed at 25p obtained for OldTownCross sequence, followed by using Rovi MainConcept version 3.2 software developed IntoTree and DucksTakeOff sequences. The same by Rovi company [9]. The characteristics of the used conclusion is available for SSIM and VQM metric. video test sequences are synthetized in Table 1. Table 1. Details of the used video sequences Test sequence Resolution@YUV Frame Rate CrowdRun 2160x3840@4:2:0 25p DucksTakeOff 2160x3840@4:2:0 25p IntoTree 2160x3840@4:2:0 25p OldTownCross 2160x3840@4:2:0 25p ParkJoy 2160x3840@4:2:0 25p The tool used for encoding process is MediaCoder Premium [10]. MediaCoder software incorporates x264 codec for H.264/AVC reference standard implementation, respectively x265 codec for H.265 reference standard implementation. The bit rate was set in the range of 8-16 Mbps having the step of 2 Mbps. The parameters selected for encoding in MediaCoder interface are given in Table 2 below for both codecs: Figure 1. Standard video test sequences used (from left- right, top-bottom): CrowdRun, ParkJoy, IntoTree, DucksTakeOff, OldTownCross Table 2. Details of the used sequence Rate Mode Constant Bit Rate Video Bit Rate [Mbps] 8,10,12,14,16 Encoder for H.264 and H.265 x.264 and x.265 Profile for H.264 and H.265 High/ Main Profile Level for both codecs 5.1/5.1 Preset for both codecs Medium GOP for both codecs 25 B-frames for x.264 3 B-frames for x.265 4 Motion Estimation for both Hexagonal codecs Motion Estimation range for 17 x.264 Motion Estimation range for 57 x.265 The objective video quality metrics used are: PSNR (Peak Signal Noise Ratio), SSIM (Structural Similarity Index) and VQM (Video Quality Measure). The above video quality metrics were computed in Elecard Video Quality Measurement Tool developed by Elecard company [11]. The Elecard VQM software use DirectShow technology for decoding compressed video stream. The program supports also several YUV and AVI uncompressed video formats. The user has the possibility 6 ISSN 1843-6188 Scientific Bulletin of the Electrical Engineering Faculty – Year 15 No.1 (29) Figure 2. PSNR-YUV quality versus bit rate Figure 3. SSIM-YUV quality versus bit rate 7 Scientific Bulletin of the Electrical Engineering Faculty – Year 15 No.1 (29) ISSN 1843-6188 [3] ITU-T Recommendation H.265 – High Efficiency Video Coding, http://www.itu.int/rec/T-REC-H.265. [4] Shanableh, T.; Peixoto, E.; Izquierdo, E., MPEG-2 to HEVC Video Transcoding With Content-Based Modeling, Circuits and Systems for Video Technology, IEEE Transactions on , vol.23, no.7, pp.1191,1196, July 2013. [5] Uhrina M., Frnda J., Sevcik L., Vaculik M., Impact of H.264/AVC and H.265/HEVC Compression Standards on the Video Quality for 4K resolution, Digital image processing and computer graphics, pp.368-376, vol. 12, no. 4, 2014. [6] Bodecek, K.; Novotny, V., From Standard Definition to High Definition Migration in Current Digital Video Broadcasting, International Multi- Conference on Computing in the Global Information Technology, ICCGI 2007, pp.15-15, 4-9 March 2007.