[FFmpeg-devel] [PATCH] opusdec: do not fail when LBRR frames are present

[Lynne]

On 11/09/2020 19:37, Anton Khirnov wrote:
> Decode and discard them.
> 
> Fixes ticket 4641.
> ---
>  libavcodec/opus_silk.c | 28 ++++++++++++++++++++--------
>  libavcodec/opustab.c   |  3 +++
>  libavcodec/opustab.h   |  3 +++
>  3 files changed, 26 insertions(+), 8 deletions(-)
> 
> diff --git a/libavcodec/opus_silk.c b/libavcodec/opus_silk.c
> index 2fcbf3b9d3..c683b25a20 100644
> --- a/libavcodec/opus_silk.c
> +++ b/libavcodec/opus_silk.c
> @@ -506,7 +506,8 @@ static inline void silk_decode_excitation(SilkContext *s, OpusRangeCoder *rc,
>  #define LTP_ORDER 5
>  
>  static void silk_decode_frame(SilkContext *s, OpusRangeCoder *rc,
> -                              int frame_num, int channel, int coded_channels, int active, int active1)
> +                              int frame_num, int channel, int coded_channels,
> +                              int active, int active1, int redundant)
>  {
>      /* per frame */
>      int voiced;       // combines with active to indicate inactive, active, or active+voiced
> @@ -665,8 +666,8 @@ static void silk_decode_frame(SilkContext *s, OpusRangeCoder *rc,
>      silk_decode_excitation(s, rc, residual + SILK_MAX_LAG, qoffset_high,
>                             active, voiced);
>  
> -    /* skip synthesising the side channel if we want mono-only */
> -    if (s->output_channels == channel)
> +    /* skip synthesising the output if we do not need it */
> +    if (s->output_channels == channel || redundant)
>          return;

Maybe add a small TODO in the comment to actually implement error recovery?


>  
>      /* generate the output signal */
> @@ -814,15 +815,26 @@ int ff_silk_decode_superframe(SilkContext *s, OpusRangeCoder *rc,
>              active[i][j] = ff_opus_rc_dec_log(rc, 1);
>  
>          redundancy[i] = ff_opus_rc_dec_log(rc, 1);
> -        if (redundancy[i]) {
> -            avpriv_report_missing_feature(s->avctx, "LBRR frames");
> -            return AVERROR_PATCHWELCOME;
> -        }
>      }
>  
> +    /* read the per-frame LBRR flags */
> +    for (i = 0; i < coded_channels; i++)
> +        if (redundancy[i] && duration_ms > 20) {
> +            redundancy[i] = ff_opus_rc_dec_cdf(rc, duration_ms == 40 ?
> +                                                   ff_silk_model_lbrr_flags_40 : ff_silk_model_lbrr_flags_60);
> +        }
> +
> +    /* decode the LBRR frames */
> +    for (i = 0; i < nb_frames; i++)
> +        for (j = 0; j < coded_channels; j++)
> +            if (redundancy[j] & (1 << i)) {
> +                int active1 = (j == 0 && !(redundancy[1] & (1 << i))) ? 0 : 1;
> +                silk_decode_frame(s, rc, i, j, coded_channels, 1, active1, 1);
> +            }

nit: add brackets to the nb_frames loop

Apart from that LGTM.

Shouldn't be too difficult to implement proper error recovery in the
future, though it would have to be a setting, because 1-frame delay is
still a 1-frame delay.