[FFmpeg-devel] [PATCH 3/3] avcodec/mpeg4video: Detect reference studio streams as studio streams

[Kieran Kunhya]

On Sun, 29 Apr 2018 at 22:57 Michael Niedermayer <michael at niedermayer.cc>
wrote:

> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libavcodec/mpeg4video.h    |  2 ++
>  libavcodec/mpeg4videodec.c | 25 ++++++++++++++++---------
>  2 files changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/libavcodec/mpeg4video.h b/libavcodec/mpeg4video.h
> index f974792887..dd0a59038d 100644
> --- a/libavcodec/mpeg4video.h
> +++ b/libavcodec/mpeg4video.h
> @@ -41,6 +41,8 @@
>  #define NBIT_VO_TYPE             5
>  #define ARTS_VO_TYPE            10
>  #define ACE_VO_TYPE             12
> +#define SIMPLE_STUDIO_VO_TYPE   14
> +#define CORE_STUDIO_VO_TYPE     15
>  #define ADV_SIMPLE_VO_TYPE      17
>
>  #define VOT_VIDEO_ID 1
> diff --git a/libavcodec/mpeg4videodec.c b/libavcodec/mpeg4videodec.c
> index ada5cdc6fa..d2b5e90331 100644
> --- a/libavcodec/mpeg4videodec.c
> +++ b/libavcodec/mpeg4videodec.c
> @@ -46,6 +46,8 @@
>  #define MB_TYPE_B_VLC_BITS 4
>  #define STUDIO_INTRA_BITS 9
>
> +static int decode_studio_vol_header(Mpeg4DecContext *ctx, GetBitContext
> *gb);
> +
>  static VLC dc_lum, dc_chrom;
>  static VLC sprite_trajectory;
>  static VLC mb_type_b_vlc;
> @@ -2049,6 +2051,18 @@ static int decode_vol_header(Mpeg4DecContext *ctx,
> GetBitContext *gb)
>      /* vol header */
>      skip_bits(gb, 1);                   /* random access */
>      s->vo_type = get_bits(gb, 8);
> +
> +    if (s->vo_type == CORE_STUDIO_VO_TYPE ||
> +        s->vo_type == SIMPLE_STUDIO_VO_TYPE) {
> +        if (s->avctx->profile != FF_PROFILE_UNKNOWN && s->avctx->profile
> != FF_PROFILE_MPEG4_SIMPLE_STUDIO)
> +            return AVERROR_INVALIDDATA;
> +        s->studio_profile = 1;
> +        s->avctx->profile = FF_PROFILE_MPEG4_SIMPLE_STUDIO;
> +        return decode_studio_vol_header(ctx, gb);
> +    } else if (s->studio_profile) {
> +        return AVERROR_PATCHWELCOME;
> +    }
> +
>      if (get_bits1(gb) != 0) {           /* is_ol_id */
>          vo_ver_id = get_bits(gb, 4);    /* vo_ver_id */
>          skip_bits(gb, 3);               /* vo_priority */
> @@ -3001,8 +3015,6 @@ static int decode_studio_vol_header(Mpeg4DecContext
> *ctx, GetBitContext *gb)
>      int width, height;
>      int bits_per_raw_sample;
>
> -            skip_bits1(gb); /* random_accessible_vol */
> -            skip_bits(gb, 8); /* video_object_type_indication */
>              skip_bits(gb, 4); /* video_object_layer_verid */
>

Please add a comment explaining what you've done here, someone might look
at this code in 10 years time (exactly like I did) and not understand why
you are mixing normal vol header and studio vol header.

Kieran