dpx: use aligned line starts

SMPTE 268M-2003 specifies that each line starts at a 4-bytes boundary.
Therefore, modify correspondingly the input buffer strides and size.

Partially fixes ticket #3692: DLAD_8b_3c_big.dpx still has inverted
colors, which might be related to endianness.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/dpx.c

@@ -77,9 +77,9 @@ static int decode_frame(AVCodecContext *avctx,
 
     unsigned int offset;
     int magic_num, endian;
-    int x, y, i, ret;
-    int w, h, bits_per_color, descriptor, elements, packing, total_size;
-    int encoding;
+    int x, y, stride, i, ret;
+    int w, h, bits_per_color, descriptor, elements, packing;
+    int encoding, need_align = 0;
 
     unsigned int rgbBuffer = 0;
     int n_datum = 0;
@@ -185,24 +185,24 @@ static int decode_frame(AVCodecContext *avctx,
 
     switch (bits_per_color) {
     case 8:
-        total_size = avctx->width * avctx->height * elements;
+        stride = avctx->width * elements;
         break;
     case 10:
         if (!packing) {
             av_log(avctx, AV_LOG_ERROR, "Packing to 32bit required\n");
             return -1;
         }
-        total_size = (avctx->width * elements + 2) / 3 * 4 * avctx->height;
+        stride = (avctx->width * elements + 2) / 3 * 4;
         break;
     case 12:
         if (!packing) {
             av_log(avctx, AV_LOG_ERROR, "Packing to 16bit required\n");
             return -1;
         }
-        total_size = 2 * avctx->width * avctx->height * elements;
+        stride = 2 * avctx->width * elements;
         break;
     case 16:
-        total_size = 2 * avctx->width * avctx->height * elements;
+        stride = 2 * avctx->width * elements;
         break;
     case 1:
     case 32:
@@ -213,6 +213,26 @@ static int decode_frame(AVCodecContext *avctx,
         return AVERROR_INVALIDDATA;
     }
 
+    // Table 3c: Runs will always break at scan line boundaries. Packing
+    // will always break to the next 32-bit word at scan-line boundaries.
+    // Unfortunately, the encoder produced invalid files, so attempt
+    // to detect it
+    need_align = FFALIGN(stride, 4);
+    if (need_align*avctx->height + (int64_t)offset > avpkt->size) {
+        // Alignment seems unappliable, try without
+        if (stride*avctx->height + (int64_t)offset > avpkt->size) {
+            av_log(avctx, AV_LOG_ERROR, "Overread buffer. Invalid header?\n");
+            return AVERROR_INVALIDDATA;
+        } else {
+            av_log(avctx, AV_LOG_INFO, "Decoding DPX without scanline "
+                   "alignment.\n");
+            need_align = 0;
+        }
+    } else {
+        need_align -= stride;
+        stride = FFALIGN(stride, 4);
+    }
+
     switch (1000 * descriptor + 10 * bits_per_color + endian) {
     case 6081:
     case 6080:
@@ -276,10 +296,6 @@ static int decode_frame(AVCodecContext *avctx,
     for (i=0; i<AV_NUM_DATA_POINTERS; i++)
         ptr[i] = p->data[i];
 
-    if (total_size + (int64_t)offset > avpkt->size) {
-        av_log(avctx, AV_LOG_ERROR, "Overread buffer. Invalid header?\n");
-        return AVERROR_INVALIDDATA;
-    }
     switch (bits_per_color) {
     case 10:
         for (x = 0; x < avctx->height; x++) {
@@ -318,6 +334,8 @@ static int decode_frame(AVCodecContext *avctx,
                 // For 12 bit, ignore alpha
                 if (elements == 4)
                     buf += 2;
+                // Jump to next aligned position
+                buf += need_align;
             }
             for (i = 0; i < 3; i++)
                 ptr[i] += p->linesize[i];
@@ -327,7 +345,7 @@ static int decode_frame(AVCodecContext *avctx,
         elements *= 2;
     case 8:
         av_image_copy_plane(ptr[0], p->linesize[0],
-                            buf, elements * avctx->width,
+                            buf, stride,
                             elements * avctx->width, avctx->height);
         break;
     }