Implement the fields rc_max_available_vbv_use and

rc_min_vbv_overflow_use in AVCodecContext, and use their values in the
ratecontrol code rather than hardcoded ones.

See the thread: "[RFC] ratecontrol buffer size magic".
Patch by Baptiste Coudurier.

Originally committed as revision 15955 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/avcodec.h

@@ -30,7 +30,7 @@
 #include "libavutil/avutil.h"
 
 #define LIBAVCODEC_VERSION_MAJOR 52
-#define LIBAVCODEC_VERSION_MINOR  3
+#define LIBAVCODEC_VERSION_MINOR  4
 #define LIBAVCODEC_VERSION_MICRO  0
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
@@ -2283,6 +2283,20 @@ typedef struct AVCodecContext {
      * - decoding: Set by user.
      */
     int64_t request_channel_layout;
+
+    /**
+     * Ratecontrol attempt to use, at maximum, <value> of what can be used without an underflow.
+     * - encoding: Set by user.
+     * - decoding: unused.
+     */
+    float rc_max_available_vbv_use;
+
+    /**
+     * Ratecontrol attempt to use, at least, <value> times the amount needed to prevent a vbv overflow.
+     * - encoding: Set by user.
+     * - decoding: unused.
+     */
+    float rc_min_vbv_overflow_use;
 } AVCodecContext;
 
 /**

libavcodec/mpegvideo_enc.c

@@ -1231,7 +1231,7 @@ vbv_retry:
 
         if(avctx->rc_buffer_size){
             RateControlContext *rcc= &s->rc_context;
-            int max_size= rcc->buffer_index/3;
+            int max_size= rcc->buffer_index * avctx->rc_max_available_vbv_use;
 
             if(put_bits_count(&s->pb) > max_size && s->lambda < s->avctx->lmax){
                 s->next_lambda= FFMAX(s->lambda+1, s->lambda*(s->qscale+1) / s->qscale);

libavcodec/ratecontrol.c

@@ -461,7 +461,7 @@ static double modify_qscale(MpegEncContext *s, RateControlEntry *rce, double q,
             else if(d<0.0001) d=0.0001;
             q*= pow(d, 1.0/s->avctx->rc_buffer_aggressivity);
 
-            q_limit= bits2qp(rce, FFMAX((min_rate - buffer_size + rcc->buffer_index)*3, 1));
+            q_limit= bits2qp(rce, FFMAX((min_rate - buffer_size + rcc->buffer_index) * s->avctx->rc_min_vbv_overflow_use, 1));
             if(q > q_limit){
                 if(s->avctx->debug&FF_DEBUG_RC){
                     av_log(s->avctx, AV_LOG_DEBUG, "limiting QP %f -> %f\n", q, q_limit);
@@ -476,7 +476,7 @@ static double modify_qscale(MpegEncContext *s, RateControlEntry *rce, double q,
             else if(d<0.0001) d=0.0001;
             q/= pow(d, 1.0/s->avctx->rc_buffer_aggressivity);
 
-            q_limit= bits2qp(rce, FFMAX(rcc->buffer_index/3, 1));
+            q_limit= bits2qp(rce, FFMAX(rcc->buffer_index * s->avctx->rc_max_available_vbv_use, 1));
             if(q < q_limit){
                 if(s->avctx->debug&FF_DEBUG_RC){
                     av_log(s->avctx, AV_LOG_DEBUG, "limiting QP %f -> %f\n", q, q_limit);

libavcodec/utils.c

@@ -743,6 +743,8 @@ static const AVOption options[]={
 {"bits_per_raw_sample", NULL, OFFSET(bits_per_raw_sample), FF_OPT_TYPE_INT, DEFAULT, INT_MIN, INT_MAX},
 {"channel_layout", NULL, OFFSET(channel_layout), FF_OPT_TYPE_INT64, DEFAULT, 0, INT64_MAX, A|E|D, "channel_layout"},
 {"request_channel_layout", NULL, OFFSET(request_channel_layout), FF_OPT_TYPE_INT64, DEFAULT, 0, INT64_MAX, A|D, "request_channel_layout"},
+{"rc_max_vbv_use", NULL, OFFSET(rc_max_available_vbv_use), FF_OPT_TYPE_FLOAT, 1.0/3, 0.0, FLT_MAX, V|E},
+{"rc_min_vbv_use", NULL, OFFSET(rc_min_vbv_overflow_use),  FF_OPT_TYPE_FLOAT, 3,     0.0, FLT_MAX, V|E},
 {NULL},
 };