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

[James Almer]

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.

> 
> -Jun
> 
> 
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