avcodec/png: read and write stereo3d frame side data information

Use optional sTER chunk defining side-by-side stereo pair
within "Extensions to the PNG 1.2 Specification", version 1.3.0.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/pngdec.c

@@ -24,6 +24,7 @@
 #include "libavutil/avassert.h"
 #include "libavutil/bprint.h"
 #include "libavutil/imgutils.h"
+#include "libavutil/stereo3d.h"
 #include "avcodec.h"
 #include "bytestream.h"
 #include "internal.h"
@@ -1164,6 +1165,21 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
                 av_log(avctx, AV_LOG_WARNING, "Broken zTXt chunk\n");
             bytestream2_skip(&s->gb, length + 4);
             break;
+        case MKTAG('s', 'T', 'E', 'R'): {
+            AVStereo3D *stereo3d = av_stereo3d_create_side_data(p);
+            if (!stereo3d) {
+                goto fail;
+            } else if (*s->gb.buffer == 0) {
+                stereo3d->type  = AV_STEREO3D_SIDEBYSIDE;
+                stereo3d->flags = AV_STEREO3D_FLAG_INVERT;
+            } else if (*s->gb.buffer == 1) {
+                stereo3d->type  = AV_STEREO3D_SIDEBYSIDE;
+            } else {
+                 av_log(avctx, AV_LOG_WARNING, "Broken sTER chunk - unknown value\n");
+            }
+            bytestream2_skip(&s->gb, length + 4);
+            break;
+        }
         case MKTAG('I', 'E', 'N', 'D'):
             if (!(s->state & PNG_ALLIMAGE))
                 av_log(avctx, AV_LOG_ERROR, "IEND without all image\n");

libavcodec/pngenc.c

@@ -31,6 +31,7 @@
 #include "libavutil/libm.h"
 #include "libavutil/opt.h"
 #include "libavutil/color_utils.h"
+#include "libavutil/stereo3d.h"
 
 #include <zlib.h>
 
@@ -340,6 +341,7 @@ static int png_get_gama(enum AVColorTransferCharacteristic trc, uint8_t *buf)
 
 static int encode_headers(AVCodecContext *avctx, const AVFrame *pict)
 {
+    AVFrameSideData *side_data;
     PNGEncContext *s = avctx->priv_data;
 
     /* write png header */
@@ -364,6 +366,23 @@ static int encode_headers(AVCodecContext *avctx, const AVFrame *pict)
     }
     png_write_chunk(&s->bytestream, MKTAG('p', 'H', 'Y', 's'), s->buf, 9);
 
+    /* write stereoscopic information */
+    side_data = av_frame_get_side_data(pict, AV_FRAME_DATA_STEREO3D);
+    if (side_data) {
+        AVStereo3D *stereo3d = (AVStereo3D *)side_data->data;
+        switch (stereo3d->type) {
+            case AV_STEREO3D_SIDEBYSIDE:
+                s->buf[0] = ((stereo3d->flags & AV_STEREO3D_FLAG_INVERT) == 0) ? 1 : 0;
+                png_write_chunk(&s->bytestream, MKTAG('s', 'T', 'E', 'R'), s->buf, 1);
+                break;
+            case AV_STEREO3D_2D:
+                break;
+            default:
+                av_log(avctx, AV_LOG_WARNING, "Only side-by-side stereo3d flag can be defined within sTER chunk\n");
+                break;
+        }
+    }
+
     /* write colorspace information */
     if (pict->color_primaries == AVCOL_PRI_BT709 &&
         pict->color_trc == AVCOL_TRC_IEC61966_2_1) {