shithub: libvpx

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correct quantizer initialization

The encoder was not correctly catching transitions in the quantizer
deltas. If a delta_q was set, then the quantizer would be reinitialized
on every frame, but if they transitioned to 0, the quantizer would
not be reinitialized, leading to a encode-decode mismatch.

This bug was triggered by commit 999e155, which sets a Y2 delta Q
for very low base Q levels.

Change-Id: Ia6733464a55ee4ff2edbb82c0873980d345446f5

--- a/vp8/encoder/encodeframe.c

+++ b/vp8/encoder/encodeframe.c

@@ -399,13 +399,6 @@

     // Clear Zbin mode boost for default case

     cpi->zbin_mode_boost = 0;

-    // vp8cx_init_quantizer() is first called in vp8_create_compressor(). A check is added here so that vp8cx_init_quantizer() is only called

-    // when these values are not all zero.

-    if (cpi->common.y1dc_delta_q | cpi->common.y2dc_delta_q | cpi->common.uvdc_delta_q | cpi->common.y2ac_delta_q | cpi->common.uvac_delta_q)

-    {

-        vp8cx_init_quantizer(cpi);

-    }

-

     // MB level quantizer setup

     vp8cx_mb_init_quantizer(cpi, &cpi->mb);

 }

--- a/vp8/encoder/onyx_if.c

+++ b/vp8/encoder/onyx_if.c

@@ -3123,11 +3123,14 @@

     return 1;

 }

+

 static void set_quantizer(VP8_COMP *cpi, int Q)

 {

     VP8_COMMON *cm = &cpi->common;

     MACROBLOCKD *mbd = &cpi->mb.e_mbd;

+    int update = 0;

+    update |= cm->base_qindex != Q;

     cm->base_qindex = Q;

     cm->y1dc_delta_q = 0;

@@ -3138,13 +3141,19 @@

     if(Q<4)

     {

+        update |= cm->y2dc_delta_q != 4-Q;

         cm->y2dc_delta_q = 4-Q;

     }

+

     // Set Segment specific quatizers

     mbd->segment_feature_data[MB_LVL_ALT_Q][0] = cpi->segment_feature_data[MB_LVL_ALT_Q][0];

     mbd->segment_feature_data[MB_LVL_ALT_Q][1] = cpi->segment_feature_data[MB_LVL_ALT_Q][1];

     mbd->segment_feature_data[MB_LVL_ALT_Q][2] = cpi->segment_feature_data[MB_LVL_ALT_Q][2];

     mbd->segment_feature_data[MB_LVL_ALT_Q][3] = cpi->segment_feature_data[MB_LVL_ALT_Q][3];

+

+    if(update)

+        vp8cx_init_quantizer(cpi);

+

 }

 static void update_alt_ref_frame_and_stats(VP8_COMP *cpi)

-- 

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