Treat YU12 as an alias for I420. Simplify setting of inv_crop_height.

source/video_common.cc

 /*
  *  Copyright 2011 The LibYuv Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS. All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 
 #include "libyuv/video_common.h"
 
 #ifdef __cplusplus
 namespace libyuv {
 extern "C" {
 #endif
 
 #define ARRAY_SIZE(x) (int)(sizeof(x) / sizeof(x[0]))
 
 struct FourCCAliasEntry {
   uint32 alias;
   uint32 canonical;
 };
 
 static const struct FourCCAliasEntry kFourCCAliases[] = {
   {FOURCC_IYUV, FOURCC_I420},
+  {FOURCC_YU12, FOURCC_I420},
   {FOURCC_YU16, FOURCC_I422},
   {FOURCC_YU24, FOURCC_I444},
   {FOURCC_YUYV, FOURCC_YUY2},
   {FOURCC_YUVS, FOURCC_YUY2},  // kCMPixelFormat_422YpCbCr8_yuvs
   {FOURCC_HDYC, FOURCC_UYVY},
   {FOURCC_2VUY, FOURCC_UYVY},  // kCMPixelFormat_422YpCbCr8
   {FOURCC_JPEG, FOURCC_MJPG},  // Note: JPEG has DHT while MJPG does not.
   {FOURCC_DMB1, FOURCC_MJPG},
   {FOURCC_BA81, FOURCC_BGGR},  // deprecated.
   {FOURCC_RGB3, FOURCC_RAW },
@@ skipping 17 matching lines @@
   }
   // Not an alias, so return it as-is.
   return fourcc;
 }
 
 #ifdef __cplusplus
 }  // extern "C"
 }  // namespace libyuv
 #endif