EE 5359 H 264 to VC 1 Transcoding Vidhya Vijayakumar Multimedia Processing Lab MSEE University of Texas Arlington vidhya vijayakumar mavs uta edu Guided by Dr K R Rao Goals Develop a basic transcoder between H 264 to VC 1 compare against an open loop cascaded transcoder Profile selected H 264 baseline I and P VC 1 simple profile I and P What is H 264 The new industry standard High quality minimal files Scalable from 3G to HD and beyond VC 1 Informal name of the SMPTE 421M video codec Standard initially developed by Microsoft WMV 9 Supported standard for blu ray discs and windows media video What is Transcoding Converting a previously compressed video signal into another one with different format Change in bit rate frame rate frame size or even compression standard Different methods Decode fully and encode in target standard Change the bit stream format from one standard to another without undergoing the complete decoding and encoding process Why transcode H 264 to VC 1 The high definition DVD format Blue ray has mandated MPEG 2 H 264 and VC 1 as the video compression format As H 264 based and VC 1 based content and products become available transcoding in both directions will be widely used From an end user point of view any VC 1 decoder can now become twice as powerful as it was earlier An Application Scenario VC 1 VC 1 Sandro Moiron et al Video transcoding from H 264 AVC to MPEG 2 with reduced computational complexity Signal Processing Image Communication Vol 24 Issue 8 Pages 637 650 Sept 2009 Why VC1 Requires less computational power and can be decoded at full 1080i p resolution on today s off theshelf PC Delivers HD content at bit rates as low as 6 8 Mbps Advanced profile delivers compression efficiencies far superior to MPEG 2 Better visual quality when compared with H 264 before the fidelity range extensions and MPEG 2 demonstrated in independent tests Prevalent codec in Microsoft s ASF files VC 1 codecs have performed well in independent subjective quality tests More of VC1 DCT based video codec design Coding tools for interlaced video sequences as well as progressive encoding 8 bit 4 2 0 format Uses block based transform and motion compensation with quantization and entropy coding VC 1 Profiles Simple Main Advanced Baseline intra frame compression Yes Yes Yes Variable sized transform Yes Yes Yes 16 bit transform Yes Yes Yes Overlapped transform Yes Yes Yes 4 motion vectors per macroblock Yes Yes Yes pixel luminance motion compensation Yes Yes Yes pixel chrominance motion compensation No Yes Yes Start codes No Yes Yes Extended motion vectors No Yes Yes VC 1 Profiles Simple Main Advanced Loop filter No Yes Yes Dynamic resolution change No Yes Yes Adaptive macroblock quantisation No Yes Yes B frames No Yes Yes Intensity compensation No Yes Yes Range adjustment No Yes Yes Field and frame coding modes No No Yes GOP Layer No No Yes Display metadata No No Yes Transcoding Techniques Open Loop Transform Domain Transcoding Cascaded Pixel Domain Architecture Simplified DCT Domain Transcoders Cascaded DCT Domain Transcoders Open Loop Transform Domain Transcoding Supports only changes in QP in the same standard bit rate changes Drift error rounding quantization loss and clipping functions Cascaded Pixel Domain Architecture Mode decisions Motion vectors extracted and reused Complexity of the motion estimation block is eliminated which accounts for 60 Drift free Complex but suited for heterogeneous transcoding Simplified DCT Domain Transcoders Motion compensation be performed in the DCT domain Drift error rounding quantization loss and clipping functions Cascaded DCT Domain transcoders spatial temporal resolution downscaling more computationally intensive requires more memory Choice of basic transcoder architecture For H 264 to VC 1 transcoding ME MC block sizes Transform size and type H 264 supports 16x16 16x8 8x16 8x8 8x4 4x8 4x4 macroblock partitions VC 1 supports 16x16 and 8x8 H 264 supports 8x8 and 4x4 block sizes VC 1 supports 8x8 8x4 4x8 and 4x4 block sizes Hence heterogeneous transcoding in pixel domain is chosen Comparison of H 264 and VC 1 Feature VC 1 H 264 Partition sizes 16x16 and 8x8 16x16 16x8 8x16 8x8 8x4 4x8 and 4x4 Color space 4 2 0 4 2 0 4 2 2 4 4 4 Integer transform 8x8 4x8 8x4 and 4x4 4x4 8x8 available in high profile only CABAC No In main and high profiles DBF Macroblock sizes Motion vector Picture Skipped MB Yes 16x16 only Two dimensional vector offset from current position to reference frame A field or frame No data is encoded for macroblock H 264 Vs VC 1 H 264 ME MC sizes VC 1 ME MC sizes H 264 Vs VC 1 H 264 transform sizes VC 1 transform sizes Mapping the differences between H 264 and VC 1 Intra MB Mode Mapping VC 1 has no spatial intra prediction Always uses 8x8 transform block size H 264 Intra MB VC 1 Intra MB 1 Intra 16x16 any mode 4 Intra MB 8x8 4 Intra 4x4 any mode 1 Intra MB 8x8 Inter MB Mode Mapping H 264 Inter MB VC 1 Inter MB Transform size in VC 1 Inter 16x16 Inter 16x16 8x8 2 Inter 16x8 Inter 16x16 8x4 2 Inter 8x16 Inter 16x16 4x8 Inter 8x8 Inter 8x8 8x8 2 Inter 4x8 Inter 8x8 4x8 2 Inter 8x4 Inter 8x8 8x4 4 Inter 4x4 Inter 8x8 4x4 Motion vector mapping H 264 Inter MB VC 1 Inter MB Motion Vector Re use Inter 16x16 Inter 16x16 Same motion vectors 2 Inter 16x8 Inter 16x16 Average of motion vectors 2 Inter 8x16 Inter 16x16 Average of motion vectors Inter 8x8 Inter 8x8 Same motion vectors 2 Inter 4x8 Inter 8x8 Average of motion vectors 2 Inter 8x4 Inter 8x8 Average of motion vectors 4 Inter 4x4 Inter 8x8 Average of motion vectors Reference Pictures H 264 VC 1 Progress Open loop transcoder 264 YUV H 264 Encoder YUV H 264 Decoder VC1 VC 1 Encoder VC 1 Decoder YUV Progress Open loop performance Progress Open loop performance Progress Open loop performance Progress Extract information from bitstream H 264 bitstream contains information about Macroblock type P16x16 P16x8 P8x16 P8x8 I4MB I16MB Macroblock sub block type SMB8x8 SMB8x4 SMB4x8 SMB4x4 Reference picture index Motion vector x y Progress Sample extracted file Simplified VC 1 Encoder ifdef H264VC1TRANSCODER if mbType I4MB mbType I16MB pMB eMBType vc1 MBIntra for Blk 0 Blk VC1 BLOCKS PER MB Blk pMB sBlk Blk eBlkType vc1 BlkIntra else if mbType P16x16 mbType P16x8 mbType P8x16 mbType PSKIP endif Stepping forward Use extracted information to encode in VC 1 using the mapping table currently working on this Compare results with the open loop transcoder Future Work Extend the transcoder for main profile in
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