[FFmpeg-devel] [PATCH] lavc/hevc_ps: parse constraint flags for HEVC REXT

[James Almer]

On 4/1/2019 6:43 AM, Linjie Fu wrote:
> Parse all the constraint flags.
> 
> It can be passed to hw decoders to detemine the exact profile for Range
> Extension HEVC.
> 
> Signed-off-by: Linjie Fu <linjie.fu at intel.com>
> ---
>  libavcodec/hevc_ps.c | 18 +++++++++++++++---
>  libavcodec/hevc_ps.h | 10 ++++++++++
>  2 files changed, 25 insertions(+), 3 deletions(-)
> 
> diff --git a/libavcodec/hevc_ps.c b/libavcodec/hevc_ps.c
> index 80df417e4f..1365a9d640 100644
> --- a/libavcodec/hevc_ps.c
> +++ b/libavcodec/hevc_ps.c
> @@ -295,9 +295,21 @@ static int decode_profile_tier_level(GetBitContext *gb, AVCodecContext *avctx,
>      ptl->non_packed_constraint_flag = get_bits1(gb);
>      ptl->frame_only_constraint_flag = get_bits1(gb);
>  
> -    skip_bits(gb, 16); // XXX_reserved_zero_44bits[0..15]
> -    skip_bits(gb, 16); // XXX_reserved_zero_44bits[16..31]
> -    skip_bits(gb, 12); // XXX_reserved_zero_44bits[32..43]
> +    ptl->max_12bit_constraint_flag        = get_bits1(gb);
> +    ptl->max_10bit_constraint_flag        = get_bits1(gb);
> +    ptl->max_8bit_constraint_flag         = get_bits1(gb);
> +    ptl->max_422chroma_constraint_flag    = get_bits1(gb);
> +    ptl->max_420chroma_constraint_flag    = get_bits1(gb);
> +    ptl->max_monochrome_constraint_flag   = get_bits1(gb);
> +    ptl->intra_constraint_flag            = get_bits1(gb);
> +    ptl->one_picture_only_constraint_flag = get_bits1(gb);
> +    ptl->lower_bit_rate_constraint_flag   = get_bits1(gb);
> +
> +    skip_bits(gb, 16); // XXX_reserved_zero_34bits[0..15]

The first of these bits can be general_max_14bit_constraint_flag. I
suppose no hardware really supports it?

> +    skip_bits(gb, 16); // XXX_reserved_zero_34bits[16..31]
> +    skip_bits(gb, 2);  // XXX_reserved_zero_34bits[32..33]
> +
> +    ptl->inbld_flag = get_bits1(gb);

Strictly speaking, you should be checking ptl->profile_idc and
ptl->profile_compatibility_flag to parse these, as per section 7.3.3 in
the spec.
Despite the amount of bits being fixed and the default value being 0, it
would be ideal to prevent misparsing damaged samples.

>  
>      return 0;
>  }
> diff --git a/libavcodec/hevc_ps.h b/libavcodec/hevc_ps.h
> index bbaa9205ef..1c95a1848b 100644
> --- a/libavcodec/hevc_ps.h
> +++ b/libavcodec/hevc_ps.h
> @@ -182,6 +182,16 @@ typedef struct PTLCommon {
>      uint8_t interlaced_source_flag;
>      uint8_t non_packed_constraint_flag;
>      uint8_t frame_only_constraint_flag;
> +    uint8_t max_12bit_constraint_flag;
> +    uint8_t max_10bit_constraint_flag;
> +    uint8_t max_8bit_constraint_flag;
> +    uint8_t max_422chroma_constraint_flag;
> +    uint8_t max_420chroma_constraint_flag;
> +    uint8_t max_monochrome_constraint_flag;
> +    uint8_t intra_constraint_flag;
> +    uint8_t one_picture_only_constraint_flag;
> +    uint8_t lower_bit_rate_constraint_flag;
> +    uint8_t inbld_flag;
>  } PTLCommon;
>  
>  typedef struct PTL {
>