Re: [FFmpeg-devel] [PATCH 1/5] avcodec/h264_mp4toannexb_bsf: refactor start_code_size handling

["mypopy@gmail.com" <mypopy@gmail.com>]

On Fri, May 19, 2023 at 4:41 PM Zhao Zhili <quinkblack@foxmail.com> wrote:
>
> From: Zhao Zhili <zhilizhao@tencent.com>
>
> start_code_size depends on whether PS comes from out-of-band or
> in-band. Make the code more readable.
> ---
>  libavcodec/h264_mp4toannexb_bsf.c | 34 ++++++++++++++++++++++++-------
>  1 file changed, 27 insertions(+), 7 deletions(-)
>
> diff --git a/libavcodec/h264_mp4toannexb_bsf.c b/libavcodec/h264_mp4toannexb_bsf.c
> index d11be455c2..7dce1ae9b6 100644
> --- a/libavcodec/h264_mp4toannexb_bsf.c
> +++ b/libavcodec/h264_mp4toannexb_bsf.c
> @@ -43,10 +43,26 @@ typedef struct H264BSFContext {
>      int      extradata_parsed;
>  } H264BSFContext;
>
> +enum PsSource {
> +    PS_OUT_OF_BAND = -1,
> +    PS_NONE = 0,
> +    PS_IN_BAND = 1,
> +};
> +
>  static void count_or_copy(uint8_t **out, uint64_t *out_size,
> -                          const uint8_t *in, int in_size, int ps, int copy)
> +                          const uint8_t *in, int in_size, enum PsSource ps, int copy)
>  {
> -    uint8_t start_code_size = ps < 0 ? 0 : *out_size == 0 || ps ? 4 : 3;
> +    uint8_t start_code_size;
> +
> +    if (ps == PS_OUT_OF_BAND)
> +        /* start code already present in out-of-band ps data, so don't need to
> +         * add it manually again
> +         */
> +        start_code_size = 0;
> +    else if (ps == PS_IN_BAND || *out_size == 0)
> +        start_code_size = 4;
> +    else
> +        start_code_size = 3;
I prefer the original style, they are shorter and more concise
>
>      if (copy) {
>          memcpy(*out + start_code_size, in, in_size);
> @@ -202,6 +218,7 @@ static int h264_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *opkt)
>
>          do {
>              uint32_t nal_size = 0;
> +            enum PsSource ps;
>
>              /* possible overread ok due to padding */
>              for (int i = 0; i < s->length_size; i++)
> @@ -230,7 +247,7 @@ static int h264_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *opkt)
>                      if (!s->sps_size) {
>                          LOG_ONCE(ctx, AV_LOG_WARNING, "SPS not present in the stream, nor in AVCC, stream may be unreadable\n");
>                      } else {
> -                        count_or_copy(&out, &out_size, s->sps, s->sps_size, -1, j);
> +                        count_or_copy(&out, &out_size, s->sps, s->sps_size, PS_OUT_OF_BAND, j);
>                          sps_seen = 1;
>                      }
>                  }
> @@ -246,19 +263,22 @@ static int h264_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *opkt)
>              if (new_idr && unit_type == H264_NAL_IDR_SLICE && !sps_seen && !pps_seen) {
>                  if (ctx->par_out->extradata)
>                      count_or_copy(&out, &out_size, ctx->par_out->extradata,
> -                                  ctx->par_out->extradata_size, -1, j);
> +                                  ctx->par_out->extradata_size, PS_OUT_OF_BAND, j);
>                  new_idr = 0;
>              /* if only SPS has been seen, also insert PPS */
>              } else if (new_idr && unit_type == H264_NAL_IDR_SLICE && sps_seen && !pps_seen) {
>                  if (!s->pps_size) {
>                      LOG_ONCE(ctx, AV_LOG_WARNING, "PPS not present in the stream, nor in AVCC, stream may be unreadable\n");
>                  } else {
> -                    count_or_copy(&out, &out_size, s->pps, s->pps_size, -1, j);
> +                    count_or_copy(&out, &out_size, s->pps, s->pps_size, PS_OUT_OF_BAND, j);
>                  }
>              }
>
> -            count_or_copy(&out, &out_size, buf, nal_size,
> -                          unit_type == H264_NAL_SPS || unit_type == H264_NAL_PPS, j);
> +            if (unit_type == H264_NAL_SPS || unit_type == H264_NAL_PPS)
> +                ps = PS_IN_BAND;
> +            else
> +                ps = PS_NONE;
> +            count_or_copy(&out, &out_size, buf, nal_size, ps, j);
>              if (!new_idr && unit_type == H264_NAL_SLICE) {
>                  new_idr  = 1;
>                  sps_seen = 0;
> --
> 2.25.1
>
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-- 
=======================================
Jun zhao/赵军
+++++++++++++++++++++++++++++++++++++++
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