[FFmpeg-devel] [PATCH, v2] lavc/hevc_parser: add 4 bytes startcode condition and update FATE

[Fu, Linjie]

> -----Original Message-----
> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf
> Of Mark Thompson
> Sent: Monday, December 10, 2018 01:40
> To: ffmpeg-devel at ffmpeg.org
> Subject: Re: [FFmpeg-devel] [PATCH, v2] lavc/hevc_parser: add 4 bytes
> startcode condition and update FATE
> 
> On 07/12/2018 11:33, Linjie Fu wrote:
> > The startcode before VPS,SPS,PPS and the first NALU in an AU is 4 bytes.
> > Blindly taking the startcode as 3 bytes will leave 0x00 in last packet
> > and may lead to some warnings in parse_nal_units when s->flags is set to
> > PARSER_FLAG_COMPLETE_FRAMES.
> >
> > Add 4 bytes startcode condition in hevc_find_frame_end.
> > Modify the code to print the buf_size like in H264 and reduce the
> duplication.
> >
> > Update the FATE checksum for fate-hevc-bsf-mp4toannexb:
> > The ref output has redundant 0x00 at the end of the SUFFIX_SEI:
> > { 50 01 84 31 00 19 39 77 d0 7b 3f bd 1e 09 38 9a 79 41
> > c0 16 11 da 18 aa 0a db 2b 19 fa 47 3f 0f 67 4a 91 9c a1
> > 12 72 67 d6 f0 8f 66 ee 95 f9 e2 b9 ba 23 9a e8 80 00 }
> >
> > To verify the output of FATE:
> > ffmpeg -i hevc-conformance/WPP_A_ericsson_MAIN10_2.bit -c copy -flags
> \
> >         +bitexact hevc-mp4.mov
> > ffmpeg -i hevc-mp4.mov -c:v copy -fflags +bitexact -f hevc hevc.out
> >
> > Signed-off-by: Linjie Fu <linjie.fu at intel.com>
> > ---
> > [v2]: Update FATE checksum
> >
> >  libavcodec/hevc_parser.c | 15 ++++++++++-----
> >  tests/fate/hevc.mak      |  2 +-
> >  2 files changed, 11 insertions(+), 6 deletions(-)
> >
> > diff --git a/libavcodec/hevc_parser.c b/libavcodec/hevc_parser.c
> > index 369d1338d0..aa216e3c8d 100644
> > --- a/libavcodec/hevc_parser.c
> > +++ b/libavcodec/hevc_parser.c
> > @@ -32,6 +32,7 @@
> >  #include "parser.h"
> >
> >  #define START_CODE 0x000001 ///< start_code_prefix_one_3bytes
> > +#define START_CODE_4 0x00000001 ///< start_code_4bytes
> 
> (There is no syntax element called "start_code_4bytes".)
> 
> >
> >  #define IS_IRAP_NAL(nal) (nal->type >= 16 && nal->type <= 23)
> >  #define IS_IDR_NAL(nal) (nal->type == HEVC_NAL_IDR_W_RADL || nal-
> >type == HEVC_NAL_IDR_N_LP)
> > @@ -239,7 +240,7 @@ static int parse_nal_units(AVCodecParserContext *s,
> const uint8_t *buf,
> >          }
> >      }
> >      /* didn't find a picture! */
> > -    av_log(avctx, AV_LOG_ERROR, "missing picture in access unit\n");
> > +    av_log(avctx, AV_LOG_ERROR, "missing picture in access unit with
> size %d\n", buf_size);
> >      return -1;
> >  }
> >
> > @@ -267,8 +268,7 @@ static int
> hevc_find_frame_end(AVCodecParserContext *s, const uint8_t *buf,
> >          if ((nut >= HEVC_NAL_VPS && nut <= HEVC_NAL_EOB_NUT) || nut ==
> HEVC_NAL_SEI_PREFIX ||
> >              (nut >= 41 && nut <= 44) || (nut >= 48 && nut <= 55)) {
> >              if (pc->frame_start_found) {
> > -                pc->frame_start_found = 0;
> > -                return i - 5;
> > +                goto found;
> >              }
> >          } else if (nut <= HEVC_NAL_RASL_R ||
> >                     (nut >= HEVC_NAL_BLA_W_LP && nut <= HEVC_NAL_CRA_NUT))
> {
> > @@ -277,14 +277,19 @@ static int
> hevc_find_frame_end(AVCodecParserContext *s, const uint8_t *buf,
> >                  if (!pc->frame_start_found) {
> >                      pc->frame_start_found = 1;
> >                  } else { // First slice of next frame found
> > -                    pc->frame_start_found = 0;
> > -                    return i - 5;
> > +                    goto found;
> >                  }
> >              }
> >          }
> >      }
> >
> >      return END_NOT_FOUND;
> > +
> > +found:
> > +    pc->frame_start_found = 0;
> > +    if (((pc->state64 >> 3 * 8) & 0xFFFFFFFF) == START_CODE_4)
> > +        return i - 6;
> > +    return i - 5;
> >  }
> 
> Maybe?  Special-casing four bytes doesn't make me feel good about this,
> given that leading_zero_8bits can be included as many times as you like at
> the beginning of a NAL unit.
> 
> If there are a large number of zeroes between two frames, which packet do
> you want them to end up in?  This changes it from "all at the end of the first
> frame" to "all except the last one at the end of the first frame", and it's not
> immediately obvious to me why that would be the right choice.  Why not, for
> example, put all of the zeroes into the second frame?
> 
> >
> 
> Thanks,
> 
> - Mark

Hi,

Does h264_find_frame_end() has the same issue if the leading_zero_8bits is included for more times?
It seems to return i - 4 or i - 5 if the startcode is found, and could not cope with the more leading_zero_8bits situation?

---h264_parser.c
      Return i - (state & 5)
---

And I'm considering to improve this in hevc_parser according to Michael's concern:

a parser should produce the same output independant on how the input is cut
into bytsstream parts. But this would behave different depending on if the 
last 0 bytes are still in the current buffer

---hevc_parser.c
found:
    pc->frame_start_found = 0;
    while ((i - 6 >= 0 && !buf[i - 6]) || 
           (i - 6 < 0 && pc->last_index + i - 6 >= 0 && !pc->buffer[pc->last_index + i - 6]))                                                                                                              
        i--; 
    return i - 5;                                                                                                                                                                                          
}
---

Thanks,
Linjie