[FFmpeg-devel] [PATCH v1] avcodec/h264_parse: retry decoding SPS with complete NAL

[Jun Li]

On Mon, Aug 19, 2019 at 6:55 PM James Almer <jamrial at gmail.com> wrote:

> On 8/19/2019 10:39 PM, Jun Li wrote:
> > On Mon, Aug 19, 2019 at 3:45 PM James Almer <jamrial at gmail.com> wrote:
> >
> >> On 8/18/2019 10:41 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.
> >>> ---
> >>>  libavcodec/h264_parse.c | 10 ++++++++--
> >>>  1 file changed, 8 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/libavcodec/h264_parse.c b/libavcodec/h264_parse.c
> >>> index ac31f54e07..a2267a0610 100644
> >>> --- a/libavcodec/h264_parse.c
> >>> +++ b/libavcodec/h264_parse.c
> >>> @@ -376,8 +376,14 @@ 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;
> >>> +                av_log(logctx, AV_LOG_DEBUG,
> >>> +                   "SPS decoding failure (maybe missing
> >> rbsp_stop_one_bit), trying again with the complete NAL\n");
> >>> +                init_get_bits8(&tmp_gb, nal->raw_data + 1,
> >> nal->raw_size - 1);
> >>> +                if ((ret = ff_h264_decode_seq_parameter_set(&tmp_gb,
> >> logctx, ps, 0)) < 0)
> >>> +                    goto fail;
> >>> +            }
> >>>              break;
> >>>          case H264_NAL_PPS:
> >>>              ret = ff_h264_decode_picture_parameter_set(&nal->gb,
> >> logctx, ps,
> >>
> >> Copy instead the code from decode_nal_units() in h264dec.c, which checks
> >> first with the complete NAL, and then calls
> >> ff_h264_decode_seq_parameter_set() with the ignore_truncation parameter
> >> set to 1 as a last resort.
> >>
> >
> > Hi James,
> > My first try was set the ignore_truncation to 1 but then found that
> > decode_nal_units is already handling this using a different approach.
> > So I just copied the code here, but without last try ignore_truncation=1.
> >
> > Are you suggesting modifying the commit message or comment identifying
> the
> > code is copied from decide_nal_units, or extract them to one function and
> > reuse two places ?
>
> My suggestion was to copy the decode_nal_units approach here including
> the last try ignore_truncation=1 call.


Thanks for the input, I updated version 2 accordingly.
https://patchwork.ffmpeg.org/patch/14604/


>
>
> > -Jun
> >
> >
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