[vlc-commits] [Git][videolan/vlc][master] 3 commits: packetizer: h264: use num_slice_groups_minus1 as stored

[Steve Lhomme (@robUx4)]

Steve Lhomme pushed to branch master at VideoLAN / VLC


Commits:
486e2e67 by Steve Lhomme at 2025-09-30T10:15:02+00:00
packetizer: h264: use num_slice_groups_minus1 as stored

And also as the specs compare it. The loop for slice_group_map_type was bogus.

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52e0d1a6 by Steve Lhomme at 2025-09-30T10:15:02+00:00
packetizer: h264: simplify sliceGroupSize computation

num_slice_groups_minus1 can only be in the [1,7] range when reaching this code.

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1327a621 by Steve Lhomme at 2025-09-30T10:15:02+00:00
packetizer: h264: skip all slice group ID's at once

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1 changed file:

- modules/packetizer/h264_nal.c


Changes:

=====================================
modules/packetizer/h264_nal.c
=====================================
@@ -563,20 +563,20 @@ static bool h264_parse_picture_parameter_set_rbsp( bs_t *p_bs,
     bs_skip( p_bs, 1 ); // entropy coding mode flag
     p_pps->i_pic_order_present_flag = bs_read( p_bs, 1 );
 
-    unsigned num_slice_groups = bs_read_ue( p_bs ) + 1;
-    if( num_slice_groups > 8 ) /* never has value > 7. Annex A, G & J */
+    unsigned num_slice_groups_minus1 = bs_read_ue( p_bs );
+    if( num_slice_groups_minus1 > 7 ) /* never has value > 7. Annex A, G & J */
         return false;
-    if( num_slice_groups > 1 )
+    if( num_slice_groups_minus1 > 0 )
     {
         unsigned slice_group_map_type = bs_read_ue( p_bs );
         if( slice_group_map_type == 0 )
         {
-            for( unsigned i = 0; i < num_slice_groups; i++ )
+            for( unsigned i = 0; i <= num_slice_groups_minus1; i++ )
                 bs_read_ue( p_bs ); /* run_length_minus1[group] */
         }
         else if( slice_group_map_type == 2 )
         {
-            for( unsigned i = 0; i < num_slice_groups; i++ )
+            for( unsigned i = 0; i < num_slice_groups_minus1; i++ )
             {
                 bs_read_ue( p_bs ); /* top_left[group] */
                 bs_read_ue( p_bs ); /* bottom_right[group] */
@@ -590,16 +590,14 @@ static bool h264_parse_picture_parameter_set_rbsp( bs_t *p_bs,
         else if( slice_group_map_type == 6 )
         {
             unsigned pic_size_in_maps_units = bs_read_ue( p_bs ) + 1;
-            unsigned sliceGroupSize = 1;
-            while(num_slice_groups > 1)
+            // Ceil( Log2( num_slice_groups_minus1 + 1 ) )
+            static const int ceil_log2_table[8] =
             {
-                sliceGroupSize++;
-                num_slice_groups = ((num_slice_groups - 1) >> 1) + 1;
-            }
-            for( unsigned i = 0; i < pic_size_in_maps_units; i++ )
-            {
-                bs_skip( p_bs, sliceGroupSize );
-            }
+                0,1,2,2,3,3,3,3
+            };
+            unsigned sliceGroupSize = ceil_log2_table[num_slice_groups_minus1];
+            // slice_group_id[]
+            bs_skip( p_bs, sliceGroupSize * pic_size_in_maps_units );
         }
     }
 



View it on GitLab: https://code.videolan.org/videolan/vlc/-/compare/8cc1583480ab48334bfdc68a342f6850f0409884...1327a621feed33b5156bcbea701c1023355d5931

-- 
View it on GitLab: https://code.videolan.org/videolan/vlc/-/compare/8cc1583480ab48334bfdc68a342f6850f0409884...1327a621feed33b5156bcbea701c1023355d5931
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