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</o:shapelayout></xml><![endif]--></head><body lang=ZH-CN link="#0563C1" vlink="#954F72" style='text-justify-trim:punctuation'><div class=WordSection1><p class=MsoNormal><span lang=EN-US>Hi, dear experts,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>We find that bitrate can be reconfigured in ABR. However, there are some codes and comments showing that users can ONLY reconfigure bitrate in CBR:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>x264_encoder_reconfig_apply @ encoder.c:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> /* Supported reconfiguration options (1-pass only):<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> * vbv-maxrate<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> * vbv-bufsize<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> * crf<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> * bitrate (CBR only) */<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> if( !ret && rc_reconfig )<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> x264_ratecontrol_init_reconfigurable( h, 0 );<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>x264_ratecontrol_init_reconfigurable @ ratecontrol.c:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> /* We don't support changing the ABR bitrate right now,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> so if the stream starts as CBR, keep it CBR. */<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> if( rc->b_vbv_min_rate )<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> h->param.rc.i_vbv_max_bitrate = h->param.rc.i_bitrate;<o:p></o:p></span></p><p class=MsoNormal style='margin-left:21.0pt;text-indent:21.0pt'>……<span lang=EN-US><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> if( rc->b_vbv_min_rate )<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> rc->bitrate = (double)h->param.rc.i_bitrate * kilobit_size;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>That means that we can ONLY reconfigure bitrate only when b_vbv_min_rate=1, <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>and it was set when we initialized the encoder (b_init = 1) with CBR (i_vbv_max_bitrate<=i_bitrate)<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>x264_validate_parameters @ encoder.c:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> else if( h->param.rc.i_vbv_max_bitrate < h->param.rc.i_bitrate &&<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> h->param.rc.i_rc_method == X264_RC_ABR )<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> {<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> x264_log( h, X264_LOG_WARNING, "max bitrate less than average bitrate, assuming CBR\n" );<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> h->param.rc.i_bitrate = h->param.rc.i_vbv_max_bitrate;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>x264_ratecontrol_init_reconfigurable @ ratecontrol.c:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> if( b_init )<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> {<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> </span>……<span lang=EN-US><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> rc->b_vbv_min_rate = !rc->b_2pass<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> && h->param.rc.i_rc_method == X264_RC_ABR<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> && h->param.rc.i_vbv_max_bitrate <= h->param.rc.i_bitrate;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> }<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>However, if we initialize the encoder with ABR (i.e. --bitrate 499 --vbv-maxrate 500 --vbv-bufsize 500),<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>then we call x264_encoder_reconfig to reconfigure bitrate (i.e param.rc.i_bitrate = 100, param.rc.i_vbv_max_bitrate = 100, param.rc. i_vbv_buffer_size = 500),<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>the new values in param.rc will be copy to h->reconfig_h->param.rc DIRECTLY in x264_encoder_try_reconfig:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>int x264_encoder_reconfig( x264_t *h, x264_param_t *param )<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>{<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> h = h->thread[h->thread[0]->i_thread_phase];<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> x264_param_t param_save = h->reconfig_h->param;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> h->reconfig_h->param = h->param;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US> int rc_reconfig;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> int ret = x264_encoder_try_reconfig( h->reconfig_h, param, &rc_reconfig );<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> if( !ret )<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> h->reconfig = 1;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> else<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> h->reconfig_h->param = param_save;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US> return ret;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>}<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>x264_encoder_try_reconfig@encoder.c:<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> /* VBV can't be turned on if it wasn't on to begin with */<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> if( h->param.rc.i_vbv_max_bitrate > 0 && h->param.rc.i_vbv_buffer_size > 0 &&<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> param->rc.i_vbv_max_bitrate > 0 && param->rc.i_vbv_buffer_size > 0 )<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> {<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> *rc_reconfig |= h->param.rc.i_vbv_max_bitrate != param->rc.i_vbv_max_bitrate;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> *rc_reconfig |= h->param.rc.i_vbv_buffer_size != param->rc.i_vbv_buffer_size;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> *rc_reconfig |= h->param.rc.i_bitrate != param->rc.i_bitrate;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> COPY( rc.i_vbv_max_bitrate );<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> COPY( rc.i_vbv_buffer_size );<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> COPY( rc.i_bitrate );<o:p></o:p></span></p><p class=MsoNormal style='text-indent:21.0pt'><span lang=EN-US>}<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>After that, h->reconfig=1, and x264_encoder_reconfig_apply will be called in x264_encoder_encode,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Then, the new values in h->reconfig_h->param.rc will be copy to h->param.rc DIRECTLY in x264_encoder_try_reconfig.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>As a result, the checking “if the stream starts as CBR, keep it CBR”in x264_ratecontrol_init_reconfigurable will not take effects because new values have been set into h->param.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>X264_encoder_encode@encoder.c<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> if( h->reconfig )<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> {<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> x264_encoder_reconfig_apply( h, &h->reconfig_h->param );<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> h->reconfig = 0;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> }<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>int x264_encoder_reconfig_apply( x264_t *h, x264_param_t *param )<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>{<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> int rc_reconfig;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> int ret = x264_encoder_try_reconfig( h, param, &rc_reconfig );<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US> mbcmp_init( h );<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> if( !ret )<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> x264_sps_init_reconfigurable( h->sps, &h->param );<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US> /* Supported reconfiguration options (1-pass only):<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> * vbv-maxrate<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> * vbv-bufsize<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> * crf<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> * bitrate (CBR only) */<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> if( !ret && rc_reconfig )<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US> x264_ratecontrol_init_reconfigurable( h, 0 );<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US> return ret;<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>}<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Therefore, we can change the bitrate in ABR indeed.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>I wonder whether reconfigure bitrate in ABR is by design (the comments and checking codes are legacy) or not (this reconfiguration behavior is unexpected) ?<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Thanks,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Zhenan<o:p></o:p></span></p></div></body></html>