What is the exactly CBR in x264?

xkfz007 · 15th November 2013, 12:32

Today I read some material from Internet about rate control of x264 and I learned what is the ABR mode. When only the param --bitrate is set, ABR mode is used. But I am confused about the CBR mode.
At first I think when the params --vbv-maxrate and --vbv-bufsize are set together with --bitrate , the CBR mode is used. Then I see these codes from x264:

Code:

  s += sprintf( s, " rc=%s mbtree=%d", p->rc.i_rc_method == X264_RC_ABR ?
                               ( p->rc.b_stat_read ? "2pass" : p->rc.i_vbv_max_bitrate == p->rc.i_bitrate ? "cbr" : "abr" )
                               : p->rc.i_rc_method == X264_RC_CRF ? "crf" : "cqp", p->rc.b_mb_tree );

Apparently, only the situation that vbv-maxrate equals bitrate, it is CBR. When the vbv-maxrate is greater than bitrate, it is still ABR mode. I want to confirm if it is correct.

15th November 2013, 12:32	#1 \| Link
xkfz007 Registered User Join Date: Sep 2013 Posts: 38	What is the exactly CBR in x264? Today I read some material from Internet about rate control of x264 and I learned what is the ABR mode. When only the param --bitrate is set, ABR mode is used. But I am confused about the CBR mode. At first I think when the params --vbv-maxrate and --vbv-bufsize are set together with --bitrate , the CBR mode is used. Then I see these codes from x264: Code: s += sprintf( s, " rc=%s mbtree=%d", p->rc.i_rc_method == X264_RC_ABR ? ( p->rc.b_stat_read ? "2pass" : p->rc.i_vbv_max_bitrate == p->rc.i_bitrate ? "cbr" : "abr" ) : p->rc.i_rc_method == X264_RC_CRF ? "crf" : "cqp", p->rc.b_mb_tree ); Apparently, only the situation that vbv-maxrate equals bitrate, it is CBR. When the vbv-maxrate is greater than bitrate, it is still ABR mode. I want to confirm if it is correct.