[FFmpeg-devel] [PATCH 2/2] avcodec/vc1: fix decoding of old WMV3 format

[Carl Eugen Hoyos]

2019-01-11 15:36 GMT+01:00, Jerome Borsboom <jerome.borsboom at carpalis.nl>:
> The position of the B MV predicitor candidate is slightly different
> for the old WMV3 format that is indicated by RES_RTM_FLAG. This patch
> fixes the decoding artifacts in the niceday.wmv sample.

Cool!

Please mention / test ticket #6641, there are still (less) artefacts.

> Signed-off-by: Jerome Borsboom <jerome.borsboom at carpalis.nl>
> ---
>  libavcodec/vc1.c      | 5 -----
>  libavcodec/vc1_pred.c | 7 ++++++-
>  2 files changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/libavcodec/vc1.c b/libavcodec/vc1.c
> index 3581d87b57..e102b931d8 100644
> --- a/libavcodec/vc1.c
> +++ b/libavcodec/vc1.c
> @@ -379,11 +379,6 @@ int ff_vc1_decode_sequence_header(AVCodecContext
> *avctx, VC1Context *v, GetBitCo
>      } else {
>          v->res_rtm_flag = get_bits1(gb); //reserved
>      }
> -    if (!v->res_rtm_flag) {
> -        av_log(avctx, AV_LOG_ERROR,
> -               "Old WMV3 version detected, some frames may be decoded
> incorrectly\n");
> -        //return -1;
> -    }
>      //TODO: figure out what they mean (always 0x402F)
>      if (!v->res_fasttx)
>          skip_bits(gb, 16);
> diff --git a/libavcodec/vc1_pred.c b/libavcodec/vc1_pred.c
> index 0b22d9916c..1ae1e33fbe 100644
> --- a/libavcodec/vc1_pred.c
> +++ b/libavcodec/vc1_pred.c
> @@ -275,7 +275,12 @@ void ff_vc1_pred_mv(VC1Context *v, int n, int dmv_x,
> int dmv_y,
>          //in 4-MV mode different blocks have different B predictor position
>          switch (n) {
>          case 0:
> -            off = (s->mb_x > 0) ? -1 : 1;

> +            if (v->res_rtm_flag)
> +                off = s->mb_x ? -1 : 1;
> +            else {

Please add more (free) braces.

Thank you, Carl Eugen