[Libva] [PATCH 1/2] H.264 encoder: respect min QP setting

[Mark Thompson]

Signed-off-by: Mark Thompson <sw at jkqxz.net>
---
This is helpful to avoid some extremes of the CBR rate control (the QP can easily get down to 1 on a static image, which then consumes the entire HRD buffer encoding the next non-static frame with far more detail that is wanted).

The ROI code is not affected by this, it can still go below the configured min QP - I think this behaviour is the right one, but if you don't think so I update that as well.


 src/gen6_mfc_common.c | 18 +++++++++---------
 src/i965_encoder.c    |  4 +++-
 src/i965_encoder.h    |  1 +
 3 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/src/gen6_mfc_common.c b/src/gen6_mfc_common.c
index 15c0637..e8596ff 100644
--- a/src/gen6_mfc_common.c
+++ b/src/gen6_mfc_common.c
@@ -179,9 +179,9 @@ static void intel_mfc_brc_init(struct encode_state *encode_state,
         mfc_context->brc.qp_prime_y[i][SLICE_TYPE_I] = mfc_context->brc.qp_prime_y[i][SLICE_TYPE_P];
         mfc_context->brc.qp_prime_y[i][SLICE_TYPE_B] = mfc_context->brc.qp_prime_y[i][SLICE_TYPE_I];
 
-        BRC_CLIP(mfc_context->brc.qp_prime_y[i][SLICE_TYPE_I], 1, 51);
-        BRC_CLIP(mfc_context->brc.qp_prime_y[i][SLICE_TYPE_P], 1, 51);
-        BRC_CLIP(mfc_context->brc.qp_prime_y[i][SLICE_TYPE_B], 1, 51);
+        BRC_CLIP(mfc_context->brc.qp_prime_y[i][SLICE_TYPE_I], (int)encoder_context->brc.min_qp, 51);
+        BRC_CLIP(mfc_context->brc.qp_prime_y[i][SLICE_TYPE_P], (int)encoder_context->brc.min_qp, 51);
+        BRC_CLIP(mfc_context->brc.qp_prime_y[i][SLICE_TYPE_B], (int)encoder_context->brc.min_qp, 51);
     }
 }
 
@@ -318,7 +318,7 @@ int intel_mfc_brc_postpack(struct encode_state *encode_state,
     qpn = (int)(qpn + delta_qp + 0.5);
 
     /* making sure that with QP predictions we did do not leave QPs range */
-    BRC_CLIP(qpn, 1, 51);
+    BRC_CLIP(qpn, (int)encoder_context->brc.min_qp, 51);
 
     if (sts == BRC_NO_HRD_VIOLATION) { // no HRD violation
         /* correcting QPs of slices of other types */
@@ -338,9 +338,9 @@ int intel_mfc_brc_postpack(struct encode_state *encode_state,
             if (abs(qpn - BRC_I_B_QP_DIFF - qpi) > 4)
                 mfc_context->brc.qp_prime_y[next_frame_layer_id][SLICE_TYPE_I] += (qpn - BRC_I_B_QP_DIFF - qpi) >> 2;
         }
-        BRC_CLIP(mfc_context->brc.qp_prime_y[next_frame_layer_id][SLICE_TYPE_I], 1, 51);
-        BRC_CLIP(mfc_context->brc.qp_prime_y[next_frame_layer_id][SLICE_TYPE_P], 1, 51);
-        BRC_CLIP(mfc_context->brc.qp_prime_y[next_frame_layer_id][SLICE_TYPE_B], 1, 51);
+        BRC_CLIP(mfc_context->brc.qp_prime_y[next_frame_layer_id][SLICE_TYPE_I], (int)encoder_context->brc.min_qp, 51);
+        BRC_CLIP(mfc_context->brc.qp_prime_y[next_frame_layer_id][SLICE_TYPE_P], (int)encoder_context->brc.min_qp, 51);
+        BRC_CLIP(mfc_context->brc.qp_prime_y[next_frame_layer_id][SLICE_TYPE_B], (int)encoder_context->brc.min_qp, 51);
     } else if (sts == BRC_UNDERFLOW) { // underflow
         if (qpn <= qp) qpn = qp + 1;
         if (qpn > 51) {
@@ -349,8 +349,8 @@ int intel_mfc_brc_postpack(struct encode_state *encode_state,
         }
     } else if (sts == BRC_OVERFLOW) {
         if (qpn >= qp) qpn = qp - 1;
-        if (qpn < 1) { // < 0 (?) overflow with minQP
-            qpn = 1;
+        if (qpn < encoder_context->brc.min_qp) { // overflow with minQP
+            qpn = encoder_context->brc.min_qp;
             sts = BRC_OVERFLOW_WITH_MIN_QP; // bit stuffing to be done
         }
     }
diff --git a/src/i965_encoder.c b/src/i965_encoder.c
index ae31f01..3056900 100644
--- a/src/i965_encoder.c
+++ b/src/i965_encoder.c
@@ -575,8 +575,10 @@ intel_encoder_check_rate_control_parameter(VADriverContextP ctx,
         encoder_context->brc.need_reset = 1;
     }
 
-    if (encoder_context->brc.window_size != misc->window_size) {
+    if (encoder_context->brc.window_size != misc->window_size ||
+        encoder_context->brc.min_qp      != misc->min_qp) {
         encoder_context->brc.window_size = misc->window_size;
+        encoder_context->brc.min_qp      = misc->min_qp;
         encoder_context->brc.need_reset = 1;
     }
 
diff --git a/src/i965_encoder.h b/src/i965_encoder.h
index be19ce6..16a6f3f 100644
--- a/src/i965_encoder.h
+++ b/src/i965_encoder.h
@@ -92,6 +92,7 @@ struct intel_encoder_context
         unsigned int hrd_buffer_size;
         unsigned int hrd_initial_buffer_fullness;
         unsigned int window_size;
+        unsigned int min_qp;
         unsigned int need_reset;
 
         unsigned int num_roi;
-- 
2.11.0