1 files changed, 23 insertions, 42 deletions

diff --git a/vp8/encoder/firstpass.c b/vp8/encoder/firstpass.c
index b063e45af..d1b38ce55 100644
--- a/vp8/encoder/firstpass.c
+++ b/vp8/encoder/firstpass.c
@@ -357,58 +357,33 @@ static int frame_max_bits(VP8_COMP *cpi)
     int max_bits;
 
     // For CBR we need to also consider buffer fullness.
+    // If we are running below the optimal level then we need to gradually tighten up on max_bits.
     if (cpi->oxcf.end_usage == USAGE_STREAM_FROM_SERVER)
     {
-        max_bits = 2 * cpi->av_per_frame_bandwidth;
-        max_bits -= cpi->buffered_av_per_frame_bandwidth;
-        max_bits *= ((double)cpi->oxcf.two_pass_vbrmax_section / 100.0);
-    }
-    // VBR
-    else
-    {
-        // For VBR base this on the bits and frames left plus the two_pass_vbrmax_section rate passed in by the user
-        max_bits = (int)(((double)cpi->twopass.bits_left / (cpi->twopass.total_stats->count - (double)cpi->common.current_video_frame)) * ((double)cpi->oxcf.two_pass_vbrmax_section / 100.0));
-    }
-
-    // Trap case where we are out of bits
-    if (max_bits < 0)
-        max_bits = 0;
+        double buffer_fullness_ratio = (double)cpi->buffer_level / DOUBLE_DIVIDE_CHECK((double)cpi->oxcf.optimal_buffer_level);
 
-    return max_bits;
-}
+        // For CBR base this on the target average bits per frame plus the maximum sedction rate passed in by the user
+        max_bits = (int)(cpi->av_per_frame_bandwidth * ((double)cpi->oxcf.two_pass_vbrmax_section / 100.0));
 
+        // If our buffer is below the optimum level
+        if (buffer_fullness_ratio < 1.0)
+        {
+            // The lower of max_bits / 4 or cpi->av_per_frame_bandwidth / 4.
+            int min_max_bits = ((cpi->av_per_frame_bandwidth >> 2) < (max_bits >> 2)) ? cpi->av_per_frame_bandwidth >> 2 : max_bits >> 2;
 
-static int gf_group_max_bits(VP8_COMP *cpi)
-{
-    // Max allocation for a golden frame group
-    int max_bits;
+            max_bits = (int)(max_bits * buffer_fullness_ratio);
 
-    // For CBR we need to also consider buffer fullness.
-    if (cpi->oxcf.end_usage == USAGE_STREAM_FROM_SERVER)
-    {
-        max_bits = cpi->av_per_frame_bandwidth * cpi->baseline_gf_interval;
-        if (max_bits > cpi->oxcf.optimal_buffer_level)
-        {
-            max_bits -= cpi->oxcf.optimal_buffer_level;
-            max_bits += cpi->buffer_level;
+            if (max_bits < min_max_bits)
+                max_bits = min_max_bits;       // Lowest value we will set ... which should allow the buffer to refil.
         }
-        else
-        {
-            max_bits -= (cpi->buffered_av_per_frame_bandwidth
-                         - cpi->av_per_frame_bandwidth)
-                        * cpi->baseline_gf_interval;
-        }
-
-        max_bits *= ((double)cpi->oxcf.two_pass_vbrmax_section / 100.0);
     }
+    // VBR
     else
     {
         // For VBR base this on the bits and frames left plus the two_pass_vbrmax_section rate passed in by the user
         max_bits = (int)(((double)cpi->twopass.bits_left / (cpi->twopass.total_stats->count - (double)cpi->common.current_video_frame)) * ((double)cpi->oxcf.two_pass_vbrmax_section / 100.0));
-        max_bits *=  cpi->baseline_gf_interval;
     }
 
-
     // Trap case where we are out of bits
     if (max_bits < 0)
         max_bits = 0;
@@ -1626,7 +1601,7 @@ static void define_gf_group(VP8_COMP *cpi, FIRSTPASS_STATS *this_frame)
     double abs_mv_in_out_accumulator = 0.0;
     double mod_err_per_mb_accumulator = 0.0;
 
-    int max_group_bits;
+    int max_bits = frame_max_bits(cpi);     // Max for a single frame
 
     unsigned int allow_alt_ref =
                     cpi->oxcf.play_alternate && cpi->oxcf.lag_in_frames;
@@ -1988,9 +1963,8 @@ static void define_gf_group(VP8_COMP *cpi, FIRSTPASS_STATS *this_frame)
 
     // Clip cpi->twopass.gf_group_bits based on user supplied data rate
     // variability limit (cpi->oxcf.two_pass_vbrmax_section)
-    max_group_bits = gf_group_max_bits(cpi);
-    if (cpi->twopass.gf_group_bits > max_group_bits)
-        cpi->twopass.gf_group_bits = max_group_bits;
+    if (cpi->twopass.gf_group_bits > max_bits * cpi->baseline_gf_interval)
+        cpi->twopass.gf_group_bits = max_bits * cpi->baseline_gf_interval;
 
     // Reset the file position
     reset_fpf_position(cpi, start_pos);
@@ -2090,6 +2064,13 @@ static void define_gf_group(VP8_COMP *cpi, FIRSTPASS_STATS *this_frame)
             }
         }
 
+        // Apply an additional limit for CBR
+        if (cpi->oxcf.end_usage == USAGE_STREAM_FROM_SERVER)
+        {
+            if (cpi->twopass.gf_bits > (cpi->buffer_level >> 1))
+                cpi->twopass.gf_bits = cpi->buffer_level >> 1;
+        }
+
         // Dont allow a negative value for gf_bits
         if (gf_bits < 0)
             gf_bits = 0;