[WIP] Add column-based tiling.

This patch adds column-based tiling. The idea is to make each tile
independently decodable (after reading the common frame header) and
also independendly encodable (minus within-frame cost adjustments in
the RD loop) to speed-up hardware & software en/decoders if they used
multi-threading. Column-based tiling has the added advantage (over
other tiling methods) that it minimizes realtime use-case latency,
since all threads can start encoding data as soon as the first SB-row
worth of data is available to the encoder.

There is some test code that does random tile ordering in the decoder,
to confirm that each tile is indeed independently decodable from other
tiles in the same frame. At tile edges, all contexts assume default
values (i.e. 0, 0 motion vector, no coefficients, DC intra4x4 mode),
and motion vector search and ordering do not cross tiles in the same
frame.
t log

Tile independence is not maintained between frames ATM, i.e. tile 0 of
frame 1 is free to use motion vectors that point into any tile of frame
0. We support 1 (i.e. no tiling), 2 or 4 column-tiles.

The loopfilter crosses tile boundaries. I discussed this briefly with Aki
and he says that's OK. An in-loop loopfilter would need to do some sync
between tile threads, but that shouldn't be a big issue.

Resuls: with tiling disabled, we go up slightly because of improved edge
use in the intra4x4 prediction. With 2 tiles, we lose about ~1% on derf,
~0.35% on HD and ~0.55% on STD/HD. With 4 tiles, we lose another ~1.5%
on derf ~0.77% on HD and ~0.85% on STD/HD. Most of this loss is
concentrated in the low-bitrate end of clips, and most of it is because
of the loss of edges at tile boundaries and the resulting loss of intra
predictors.

TODO:
- more tiles (perhaps allow row-based tiling also, and max. 8 tiles)?
- maybe optionally (for EC purposes), motion vectors themselves
  should not cross tile edges, or we should emulate such borders as
  if they were off-frame, to limit error propagation to within one
  tile only. This doesn't have to be the default behaviour but could
  be an optional bitstream flag.

Change-Id: I5951c3a0742a767b20bc9fb5af685d9892c2c96f

2 files changed, 18 insertions, 1 deletions

diff --git a/vpx/vp8cx.h b/vpx/vp8cx.h
index 90b7169d5..79bb5827f 100644
--- a/vpx/vp8cx.h
+++ b/vpx/vp8cx.h
@@ -187,7 +187,8 @@ enum vp8e_enc_control_id {
 
 
   /* TODO(jkoleszar): Move to vp9cx.h */
-  VP9E_SET_LOSSLESS
+  VP9E_SET_LOSSLESS,
+  VP9E_SET_TILE_COLUMNS
 };
 
 /*!\brief vpx 1-D scaling mode
@@ -255,6 +256,19 @@ typedef enum {
 } vp8e_token_partitions;
 
 
+/*!\brief VP8 tile column mode
+ *
+ * This defines VP9 tiling mode for compressed data, i.e., the number of
+ * sub-streams in the bitstream. Used for parallelized encoding/decoding.
+ *
+ */
+
+typedef enum {
+  VP8_ONE_TILE_COLUMN   = 0,
+  VP8_TWO_TILE_COLUMNS  = 1,
+  VP8_FOUR_TILE_COLUMNS = 2
+} vp8e_tile_column_mode;
+
 /*!\brief VP8 model tuning parameters
  *
  * Changes the encoder to tune for certain types of input material.
@@ -298,6 +312,8 @@ VPX_CTRL_USE_TYPE(VP8E_SET_ARNR_TYPE,     unsigned int)
 VPX_CTRL_USE_TYPE(VP8E_SET_TUNING,             int) /* vp8e_tuning */
 VPX_CTRL_USE_TYPE(VP8E_SET_CQ_LEVEL,      unsigned int)
 
+VPX_CTRL_USE_TYPE(VP9E_SET_TILE_COLUMNS,  int)
+
 VPX_CTRL_USE_TYPE(VP8E_GET_LAST_QUANTIZER,     int *)
 VPX_CTRL_USE_TYPE(VP8E_GET_LAST_QUANTIZER_64,  int *)
 
diff --git a/vpx/vpx_decoder.h b/vpx/vpx_decoder.h
index dbe6aaaaa..d2dec6f5d 100644
--- a/vpx/vpx_decoder.h
+++ b/vpx/vpx_decoder.h
@@ -101,6 +101,7 @@ extern "C" {
     unsigned int threads; /**< Maximum number of threads to use, default 1 */
     unsigned int w;      /**< Width */
     unsigned int h;      /**< Height */
+    int inv_tile_order;  /**< Invert tile decoding order, default 0 */
   } vpx_codec_dec_cfg_t; /**< alias for struct vpx_codec_dec_cfg */