API: h264 decode: introduce num_emulation_prevention_bytes.

num_emulation_prevention_bytes represent the number of emulation prevention
bytes available in the slice_header(). This helps VA drivers determine how
many emulation prevention bytes there are so that to program the hardware
appropriately, without having to parse the slice_header() again.

Rationale: it is not always possible to parse the slice_header() again.
For instance, if "protected slices" are used, the slice data is uploaded
into a VAProtectedSliceDataBuffer and it is no longer possible to read
bytes from it afterwards. e.g. it could be in encrypted memory region
or protected memory region only accessible from the video decoder.

In newly written code, this member shall be filled in appropriately along
with emulation_prevention_bytes_flag set to 1.

Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/va/va.h b/va/va.h
index 2d92ce7..a8e53a2 100644
--- a/va/va.h
+++ b/va/va.h
@@ -1501,6 +1501,10 @@ typedef struct _VASliceParameterBufferH264
      *
      * Basically, this field represents the number of bits parsed in
      * the slice_header() + 8 for the initial NAL unit byte.
+     *
+     * See the "Emulation Prevention Bytes" section hereunder for more
+     * details about how slices with emulation prevention bytes need
+     * to be handled.
      */
     unsigned short slice_data_bit_offset;
     unsigned short first_mb_in_slice;
@@ -1529,6 +1533,37 @@ typedef struct _VASliceParameterBufferH264
     unsigned char chroma_weight_l1_flag;
     short chroma_weight_l1[32][2];
     short chroma_offset_l1[32][2];
+
+    /** @name Emulation Prevention Bytes */
+    /**@{*/
+    /**
+     * \brief Determines whether \ref num_emulation_prevention_bytes
+     * is set or not.
+     *
+     * \ref slice_data_bit_offset represents a bit offset from the NAL
+     * Header Unit to the begining of slice_data(). However, some VA
+     * drivers require a bit offset without emulation prevention bytes.
+     *
+     * If \ref emulation_prevention_bytes_flag is 1, then the driver
+     * will be able to determine this bit offset without parsing the
+     * slice_header() again. This is especially important for "protected
+     * slices" as once the data is uploaded to a VAProtectedSliceData
+     * buffer, the data in cyphered and no longer available to the
+     * driver.
+     *
+     * If \ref emulation_prevention_bytes_flag is 0, then the driver
+     * will parse the slice_header() and count the number of emulation
+     * prevention bytes itself and adjust the bit offset for the
+     * hardware accordingly.
+     *
+     * \ref emulation_prevention_bytes_flag shall always be set to 1
+     * for newly written code and \ref num_emulation_prevention_bytes
+     * shall be filled in appropriately.
+     */
+    unsigned char emulation_prevention_bytes_flag;
+    /** \brief Number of emulation prevention bytes in slice_header(). */
+    unsigned int num_emulation_prevention_bytes;
+    /**@}*/
 } VASliceParameterBufferH264;
 
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