[x264-devel] [PATCH] frame_num increment in non-refererence frames

[Loïc Le Loarer]

Hi,

x264 is current producing invalid streams when B frames are used because
frame_num are not correctly incremented. According to paragraph 7.4.3,
frame_num must not be equal to PrevRefFrameNum (except in special cases
when fields are used), so the frame_num must be incremented after a
reference picture but not after a non reference picture.

If I and P pictures are reference and B pictures are not reference, the
following order should be seen :
I P B B P B P P B P ...
0 1 2 2 2 3 3 4 5 5 ...

while x264 is producing :
I P B B P B P P B P ...
0 1 1 1 2 2 3 4 4 5 ...

I have made a patch which seems to correct this but I'm not enterely
sure it is really correct as I don't know the code well enough. Can you
take a look at this ?

Best regards.

-- 
Loïc

"heaven is not a place, it's a feeling"
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Index: encoder/encoder.c
===================================================================
--- encoder/encoder.c	(revision 523)
+++ encoder/encoder.c	(working copy)
@@ -864,14 +864,14 @@
     /* ------------------------ Create slice header  ----------------------- */
     if( i_nal_type == NAL_SLICE_IDR )
     {
-        x264_slice_header_init( h, &h->sh, h->sps, h->pps, i_slice_type, h->i_idr_pic_id, h->i_frame_num - 1, i_global_qp );
+        x264_slice_header_init( h, &h->sh, h->sps, h->pps, i_slice_type, h->i_idr_pic_id, h->i_frame_num, i_global_qp );
 
         /* increment id */
         h->i_idr_pic_id = ( h->i_idr_pic_id + 1 ) % 65536;
     }
     else
     {
-        x264_slice_header_init( h, &h->sh, h->sps, h->pps, i_slice_type, -1, h->i_frame_num - 1, i_global_qp );
+        x264_slice_header_init( h, &h->sh, h->sps, h->pps, i_slice_type, -1, h->i_frame_num, i_global_qp );
 
         /* always set the real higher num of ref frame used */
         h->sh.b_num_ref_idx_override = 1;
@@ -1292,12 +1292,12 @@
     if( i_slice_type == SLICE_TYPE_B )
         x264_macroblock_bipred_init( h );
 
+    /* ------------------------ Create slice header  ----------------------- */
+    x264_slice_init( h, i_nal_type, i_slice_type, i_global_qp );
+
     if( h->fenc->b_kept_as_ref )
         h->i_frame_num++;
 
-    /* ------------------------ Create slice header  ----------------------- */
-    x264_slice_init( h, i_nal_type, i_slice_type, i_global_qp );
-
     /* ---------------------- Write the bitstream -------------------------- */
     /* Init bitstream context */
     h->out.i_nal = 0;
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