[FFmpeg-devel] [RFC] support for Cam_PAL_D1_inter_Field_25fps_2.5MBS.mp4

[Reimar Döffinger]

On Thu, Mar 20, 2008 at 07:26:20PM +0100, Michael Niedermayer wrote:
> On Thu, Mar 20, 2008 at 03:43:34PM +0100, Reimar D?ffinger wrote:
> > Hello,
> > I made a patch that works for:
> > http://samples.mplayerhq.hu/V-codecs/h264/PAFF/Cam_PAL_D1_inter_Field_25fps_2.5MBS.mp4
> > I think this is probably the wrong approach and instead we need an
> > AVParser for H.264 in mov, but I am not entirely sure, so please
> > have a look at attached patch.
> 
> Could you explain in english words what the problem with that file is
> and what your patch does? I could guess that its something with multiple
> fields in a packet ...

The problem with that file is,
1) only I-frames are displayed, since the code never finds a
complementary field, which I think is due to the bottom field being in
the same packet, so slice number is != 0, so the whole
check-for-complete-frame code does not run.
2) Probably related to this, also the reference pictures used are the
wrong ones, as can be seen when making FFmpeg always output a picture
even if it thinks one field is still missing.

> > Index: libavcodec/h264.c
> > ===================================================================
> > --- libavcodec/h264.c	(revision 12478)
> > +++ libavcodec/h264.c	(working copy)
> > @@ -3884,6 +3884,7 @@
> >  
> >      if((s->flags2 & CODEC_FLAG2_CHUNKS) && first_mb_in_slice == 0){
> >          h0->current_slice = 0;
> > +        h0->block_available_fields = 0;
> 
> It does not seem that we have such a variable in the context, and your
> patch doesnt add one ...
> 
> 
> >          if (!s0->first_field)
> >              s->current_picture_ptr= NULL;
> >      }
> > @@ -4003,7 +4004,20 @@
> >          s->picture_structure= PICT_FRAME;
> >      }else{
> >          if(get_bits1(&s->gb)) { //field_pic_flag
> > -            s->picture_structure= PICT_TOP_FIELD + get_bits1(&s->gb); //bottom_field_flag
> > +            int next_picture_structure = PICT_TOP_FIELD + get_bits1(&s->gb); //bottom_field_flag
> 
> > +            int mask = next_picture_structure == PICT_TOP_FIELD ? 1 : 2;
> 
> this is just mask = next_picture_structure

Updated, though as said I doubt it is quite the right way to do it, I am
mostly hoping for someone else to come up with a better solution after
the problem is truly clear (which I hope this patch will help to do).

Greetings,
Reimar D?ffinger
-------------- next part --------------
Index: libavcodec/h264.c
===================================================================
--- libavcodec/h264.c	(revision 12478)
+++ libavcodec/h264.c	(working copy)
@@ -3884,6 +3884,7 @@
 
     if((s->flags2 & CODEC_FLAG2_CHUNKS) && first_mb_in_slice == 0){
         h0->current_slice = 0;
+        h0->block_available_fields = 0;
         if (!s0->first_field)
             s->current_picture_ptr= NULL;
     }
@@ -4003,7 +4004,19 @@
         s->picture_structure= PICT_FRAME;
     }else{
         if(get_bits1(&s->gb)) { //field_pic_flag
-            s->picture_structure= PICT_TOP_FIELD + get_bits1(&s->gb); //bottom_field_flag
+            int next_picture_structure = PICT_TOP_FIELD + get_bits1(&s->gb); //bottom_field_flag
+            if(h0->block_available_fields == (next_picture_structure ^ 3)) {
+                if(!s->dropable) {
+                    h0->prev_poc_msb = h0->poc_msb;
+                    h0->prev_poc_lsb = h0->poc_lsb;
+                    execute_ref_pic_marking(h0, h0->mmco, h0->mmco_index);
+                }
+                h0->current_slice = 0;
+                h0->block_available_fields |= next_picture_structure;
+                return 1;
+            }
+            h0->block_available_fields |= next_picture_structure;
+            s->picture_structure = next_picture_structure;
         } else {
             s->picture_structure= PICT_FRAME;
             h->mb_aff_frame = h->sps.mb_aff;
@@ -7442,6 +7455,7 @@
 #endif
     if(!(s->flags2 & CODEC_FLAG2_CHUNKS)){
         h->current_slice = 0;
+        h->block_available_fields = 0;
         if (!s->first_field)
             s->current_picture_ptr= NULL;
     }
@@ -7600,6 +7614,10 @@
              * NAL unit stuff to context 0 and restart. Note that
              * rbsp_buffer is not transfered, but since we no longer
              * run in parallel mode this should not be an issue. */
+            if(context_count) {
+                execute_decode_slices(h, context_count);
+                context_count = 0;
+            }
             h->nal_unit_type = hx->nal_unit_type;
             h->nal_ref_idc   = hx->nal_ref_idc;
             hx = h;
Index: libavcodec/h264.h
===================================================================
--- libavcodec/h264.h	(revision 12478)
+++ libavcodec/h264.h	(working copy)
@@ -412,6 +412,8 @@
     int single_decode_warning;
 
     int last_slice_type;
+
+    int block_available_fields;
     /** @} */
 
 }H264Context;