Hi dear community,<br> I want to ask your opinion about strange results that i've obtained in frame transcoding and if is possible to find any solutions. I implement a cascade transcoder (fully decode the frame, i scale it in spatial resolution and then re-encode in h264 with x264) for frame that are receveid over ip network, I transcode it with low latency and i re-send it newly over network. <br>
In x264 encoding process i've set this parameters:<br> <br> x264_param_default( &param );<br><br> //Set video resolution<br> param.i_width = scale_width;<br> param.i_height = scale_height;<br><br> //We don't need bframe<br>
param.i_bframe = 0;<br> param.i_bframe_adaptive = 0;<br><br> //Maximum dimension of the gop<br> param.i_keyint_max = 20;<br><br> //Frame delay wait that the encoder have encoded more frame for return in<br>
//output that.<br> //With b-adapt = 0 or 1:<br> //frame_delay = MAX( param.rc.i_lookahead, param.i_bframes ) + threads - 1<br> //We remove lookahead and multiple thread for avoid frame delay.<br> param.rc.i_lookahead = 0;<br>
param.i_threads = 1;<br><br> //Gop Size maximum 20<br> param.i_keyint_max = 20;<br><br> //Setting variable bitrate<br> param.rc.i_rc_method = X264_RC_CRF;<br> //Specify quality of encoding<br> param.rc.f_rf_constant = 30;<br>
<br>I scaled from 720x576 resolution to 352x288.<br>The results that i obtain are a bit strange:<br>- if the frame that i receive is low quality, the scaled re-encoded frame have greater size (for mpeg4.3 intra frame of 15 kB, the re-encoded obtained frame is 67kB);<br>
- if i decode and scale a frame of high quality in mpeg4.3 and then re-encode in h264, i reduce the frame size by a factor of two, but the real strange fact is that i re-encode the not-resized picture i obtain a frame of the same size or less. The picture is correctly resized because i can display that after the scaling operation and the picture buffer is effectively of the correct dimension. Finally, if i transcode reducing spatial resolution an h264 high quality frame i achieve these results: from 33kB(720x576) frame to 28kB(352x288).<br>
<br>Anyone have any idea? Many thanks.<br><br>Best Regards.<br>