Multiple-resolution encoder

The example encoder down-samples the input video frames a number of
times with a down-sampling factor, and then encodes and outputs
bitstreams with different resolutions.

Support arbitrary down-sampling factor, and down-sampling factor
can be different for each encoding level.

For example, the encoder can be tested as follows.
1. Configure with multi-resolution encoding enabled:
../libvpx/configure --target=x86-linux-gcc --disable-codecs
--enable-vp8 --enable-runtime_cpu_detect --enable-debug
--disable-install-docs --enable-error-concealment
--enable-multi-res-encoding
2. Run make
3. Encode:
If input video is 1280x720, run:
./vp8_multi_resolution_encoder 1280 720 input.yuv 1.ivf 2.ivf 3.ivf 1
(output: 1.ivf(1280x720); 2.ivf(640x360); 3.ivf(320x180).
The last parameter is set to 1/0 to show/not show PSNR.)
4. Decode:
./simple_decoder 1.ivf 1.yuv
./simple_decoder 2.ivf 2.yuv
./simple_decoder 3.ivf 3.yuv
5. View video:
mplayer 1.yuv -demuxer rawvideo -rawvideo w=1280:h=720 -loop 0 -fps 30
mplayer 2.yuv -demuxer rawvideo -rawvideo w=640:h=360 -loop 0 -fps 30
mplayer 3.yuv -demuxer rawvideo -rawvideo w=320:h=180 -loop 0 -fps 30

The encoding parameters can be modified in vp8_multi_resolution_encoder.c,
for example, target bitrate, frame rate...

Modified API. John helped a lot with that. Thanks!

Change-Id: I03be9a51167eddf94399f92d269599fb3f3d54f5

vp8/encoder/onyx_int.h

@@ -58,6 +58,9 @@
 
 #define MAX_PERIODICITY 16
 
+#define MAX(x,y) (((x)>(y))?(x):(y))
+#define MIN(x,y) (((x)<(y))?(x):(y))
+
 typedef struct
 {
     int kf_indicated;
@@ -679,6 +682,11 @@ typedef struct VP8_COMP
     double total_ssimg_v_in_layer[MAX_LAYERS];
     double total_ssimg_all_in_layer[MAX_LAYERS];
 
+#if CONFIG_MULTI_RES_ENCODING
+    /* Number of MBs per row at lower-resolution level */
+    int    mr_low_res_mb_cols;
+#endif
+
 } VP8_COMP;
 
 void control_data_rate(VP8_COMP *cpi);