Using MV/SAD information from DM365 encoder in application

Transcription

1 Using MV/ information from DM365 encoder in application Version 1.0 Usage for Motion Vector and for DM365 codecs This document describes the motion vector and information passed by the DM365 encoder and the method to use it. The discussion is limited to Mpeg4 and H Description The Motion Vector Access API is part of the XDM process() call that the application uses to encode a frame. A run-time parameter is provided as a part of dynamic parameters, which can be set or reset at a frame level at run-time. Mpeg4 encoder : MataEnable H.264 encoder: mvoutflag Setting this flag to 1 indicates that the motion vectors access is needed. When this parameter is set to 1, the process() call returns the motion vector data in the buffer provided by the application. For every macro block, the data returned is 8 bytes, a signed horizontal displacement component (signed 16-bit integer) and a vertical displacement component (signed 16-bit integer) and unsigned, as shown: Motion vector horizontal displacement () Motion vector vertical displacement () Signed 16 - bit integer Signed 16 - bit integer Unsigned 32 - bit integer The API returns the motion vector data in a single buffer with these three values interleaved in contiguous memory as shown in the following figure. Page 1 of 7

2 MB(0,0) MB (0,1) MB (0, num_mb_cols -1) MB (1,0) MB (num_mb_rows -1, num_mb_cols -2) MB (num_mb_rows -1, num_mb_cols -1) Figure -1. Motion Vector and Buffer Organization. Page 2 of 7

3 1.2 Usage for Mpeg4 encoder The following sequence should be followed for motion vector access: 1) In the dynamic parameters, set the flag to access MV data: /* This structure defines the run-time parameters for MP4VEnc object */ MP4VENC_DynamicParams ext_dynamicparams; /* Enable MV access */ ext_dynamicparams ->mvdataenable = 1; /* Control call to set the dynamic parameters */ control(.., XDM_SETPARAMS,..) 2) Allocate output buffers and define the output buffer descriptors: /* Output Buffer Descriptor variables */ XDM_BufDesc outputbufdesc; /* Get the input and output buffer requirements for the codec */ control(.., XDM_GETBUFINFO, extn_dynamicparams,..); If MV access is enabled in step 1, this call will return the buffer informatin as minnumoutbufs=2, along with the minimal buffer sizes. /* Initialize the output buffer descriptor */ outputbufdesc.numbufs = status.videncstatus.bufinfo.minnumoutbufs; /* Stream Buffer */ outputbufdesc.bufs[0] = streamdataptr; //pointer to mpeg4 bit stream outputbufdesc.bufsizes[0] = status.videncstatus.bufinfo.minoutbufsize[0]; /* MV Buffer */ Page 3 of 7

4 outputbufdesc.bufs[1] to MV data = mvdtataptr; //pointer outputbufdesc.bufsizes[1] = status.videncstatus.bufinfo.minoutbufsize[1]; 3) Call the frame encode API: /* Process call to encode 1 frame */ process(..,.., outputbufdesc,.. ); After this call, the buffer outputbufdesc.bufs[1] will have the Motion vector data. This API will return the size of the MV array in outargs.mvdatasize. 1.3 Usage for H.264 encoder The following sequence should be followed for motion vector access: 1) In the dynamic parameters, set the flag to access MV data: /* This structure defines the run-time parameters for H264VEnc object */ H264VENC_DynamicParams ext_dynamicparams; /* Enable MV access */ ext_dynamicparams ->mvdataenable = 1; /* Control call to set the dynamic parameters */ control(.., XDM_SETPARAMS,..) 2) Allocate output buffers and define the output buffer descriptors: Page 4 of 7

5 /* Output Buffer Descriptor variables */ XDM_BufDesc outputbufdesc; /* Get the input and output buffer requirements for the codec */ control(.., XDM_GETBUFINFO, extn_dynamicparams,..); If multiple slice is on, then MV- information is in the index 2 of the buffers pointed by XDM_BufDesc *outbufs and index 1 is for packet size information. If multiple slice is off, the MV- is dumped in index 1 of buffer pointers. Index 0 is always used for bit-stream data. Assuming multiple slice is OFF - If MV/ is enabled in step 1, this call will return the buffer information as minnumoutbufs=2, along with the minimal buffer sizes. /* Initialize the output buffer descriptor */ outputbufdesc.numbufs = status.videncstatus.bufinfo.minnumoutbufs; /* Stream Buffer */ outputbufdesc.bufs[0] = streamdataptr; //pointer to mpeg4 bit stream outputbufdesc.bufsizes[0] = status.videncstatus.bufinfo.minoutbufsize[0]; /* MV Buffer */ outputbufdesc.bufs[1] to MV data = mvdtataptr; //pointer outputbufdesc.bufsizes[1] = status.videncstatus.bufinfo.minoutbufsize[1]; 3) Call the frame encode API: Page 5 of 7

6 /* Process call to encode 1 frame */ process(..,.., outputbufdesc,.. ); After this call, the buffer outputbufdesc.bufs[1] will have the Motion vector data. 1.4 How application can access MV information As shown in figure 1, the API uses a single buffer to store the motion vector data. The buffer will have the three values (,, ) interleaved in contiguous memory. Below is a code snippet on how an application writer can make use fo motion vector buffer returned by the codec. struct motion_mbdata { } ; short MVx; short MVy; unsigned int ; motion_mbdata *mbmv_data = outputbufdesc.bufs[1]; num_mb_rows = framerows / 16; num_mb_cols = framecols / 16; for (i = 0; i < num_mb_rows; i++) { { for (j = 0; j < num_mb_cols; j++) for mb(i, j) = mbmv_data ->MVx; for mb(i, j) = mbmv_data ->MVy; for mb(i,j) = mbmv_data ->SSE; mbmv_data ++; } } 1.5 Difference/comparison between Mpeg4 and H.264 MV/ access The below table gives a description of items which vary between Mpeg4 and H.264 Page 6 of 7

7 Items Control variable name in dynamic param Output buffer index MV data format Mpeg4 Encoder MataEnable Index 1 Same for both (see figure 1) H.264 encoder mvoutflag Index can be 1 or 2 depending on multiple slice is enabled or not Sends and not SSE/SAT Intra MB in P frame In this case, the motion vectors computed in the motion estimation stage (assuming that this macro block is inter) will be returned Motion vector precision Full pel Quarter Pel Status in outargs Intra frame Returns outargs.mvdatasize which is the size of MV/ array outargs.mvdatasize = 0 The outbuf should not be read No such status returned outbuf filled with default value, MV as 0 and as MAX(UNIT32) Page 7 of 7