avcodec/hevcdec: Avoid allocation of common CABAC state

It used to be allocated separately, so that the pointer to it
is copied to all HEVCContexts, so that all slice-threads
use the same. This is completely unnecessary now that there
is only one HEVCContext any more. There is just one minor
complication left: The slice-threads only get a pointer to
const HEVCContext, but they need to modify the common CABAC
state. Fix this by adding a pointer to the common CABAC state
to HEVCLocalContext and document why it exists.

Reviewed-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

1 files changed, 15 insertions, 2 deletions

diff --git a/libavcodec/hevcdec.h b/libavcodec/hevcdec.h
index 3367ee312a..6cef9e6f0a 100644
--- a/libavcodec/hevcdec.h
+++ b/libavcodec/hevcdec.h
@@ -439,6 +439,18 @@ typedef struct HEVCLocalContext {
     GetBitContext gb;
     CABACContext cc;
 
+    /**
+     * This is a pointer to the common CABAC state.
+     * In case entropy_coding_sync_enabled_flag is set,
+     * the CABAC state after decoding the second CTU in a row is
+     * stored here and used to initialize the CABAC state before
+     * decoding the first CTU in the next row.
+     * This is the basis for WPP and in case slice-threading is used,
+     * the next row is decoded by another thread making this state
+     * shared between threads.
+     */
+    HEVCCABACState *common_cabac_state;
+
     int8_t qp_y;
     int8_t curr_qp_y;
 
@@ -485,8 +497,6 @@ typedef struct HEVCContext {
     int                 width;
     int                 height;
 
-    HEVCCABACState *cabac;
-
     /** 1 if the independent slice segment header was successfully parsed */
     uint8_t slice_initialized;
 
@@ -559,6 +569,9 @@ typedef struct HEVCContext {
     uint16_t seq_decode;
     uint16_t seq_output;
 
+    /** The target for the common_cabac_state of the local contexts. */
+    HEVCCABACState cabac;
+
     int enable_parallel_tiles;
     atomic_int wpp_err;