[FFmpeg-devel] [PATCH v2] avcodec/h264_parse: retry decoding SPS with complete NAL

[Jun Li]

On Thu, Aug 22, 2019 at 12:00 PM James Almer <jamrial at gmail.com> wrote:

> On 8/19/2019 11:24 PM, Jun Li wrote:
> > Fix #6591
> > The content has no rbsp_stop_one_bit for ending the SPS, that
> > causes the decoding SPS failure, results decoding frame failure as well.
> >
> > The patch is just adding a retry with complete NALU, copied from the
> retry in decode_nal_unit()
> > ---
> >  libavcodec/h264_parse.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavcodec/h264_parse.c b/libavcodec/h264_parse.c
> > index ac31f54e07..ea7a958dd9 100644
> > --- a/libavcodec/h264_parse.c
> > +++ b/libavcodec/h264_parse.c
> > @@ -376,8 +376,15 @@ static int decode_extradata_ps(const uint8_t *data,
> int size, H264ParamSets *ps,
> >          switch (nal->type) {
> >          case H264_NAL_SPS:
> >              ret = ff_h264_decode_seq_parameter_set(&nal->gb, logctx,
> ps, 0);
> > -            if (ret < 0)
> > -                goto fail;
> > +            if (ret < 0) {
> > +                GetBitContext tmp_gb = nal->gb;
>
> nal->gb will already be changed here and will not be pointing to the
> start of the SPS.
>
> > +                av_log(logctx, AV_LOG_DEBUG,
> > +                   "SPS decoding failure, trying again with the
> complete NAL\n");
> > +                init_get_bits8(&tmp_gb, nal->raw_data + 1,
> nal->raw_size - 1);
>
> And you're overwriting it here, so the above assignment was pointless.
>
> > +                if ((ret = ff_h264_decode_seq_parameter_set(&tmp_gb,
> logctx, ps, 0)) < 0 &&
> > +                    (ret = ff_h264_decode_seq_parameter_set(&tmp_gb,
> logctx, ps, 1)) < 0)
>
> Similarly, tmp_gb will be not be pointing to the start of the SPS if the
> second ff_h264_decode_seq_parameter_set() call (with truncation enabled)
> is ever executed.
>
> > +                    goto fail;
> > +            }
> >              break;
> >          case H264_NAL_PPS:
> >              ret = ff_h264_decode_picture_parameter_set(&nal->gb,
> logctx, ps,
> >
>
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Thanks a lot James for pointing it out. Sorry about those obvious bugs.
I updated the version accordingly https://patchwork.ffmpeg.org/patch/14660/

-Jun