[FFmpeg-devel] [PATCH v1] avcodec/h264_metadata_bsf: add option to delete SEI user data

[Mark Thompson]

On 20/04/2020 12:01, lance.lmwang at gmail.com wrote:
> From: Limin Wang <lance.lmwang at gmail.com>
> 
> Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
> ---
>  doc/bitstream_filters.texi     |  3 +++
>  libavcodec/h264_metadata_bsf.c | 19 +++++++++++++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/doc/bitstream_filters.texi b/doc/bitstream_filters.texi
> index 8fe5b3ad75..652eb4620f 100644
> --- a/doc/bitstream_filters.texi
> +++ b/doc/bitstream_filters.texi
> @@ -273,6 +273,9 @@ possibly separated by hyphens, and the string can be anything.
>  For example, @samp{086f3693-b7b3-4f2c-9653-21492feee5b8+hello} will
>  insert the string ``hello'' associated with the given UUID.
>  
> + at item delete_user_data
> +Deletes all SEI user data messages.
> +
>  @item delete_filler
>  Deletes both filler NAL units and filler SEI messages.
>  
> diff --git a/libavcodec/h264_metadata_bsf.c b/libavcodec/h264_metadata_bsf.c
> index d96a50dbf7..8b42faff1b 100644
> --- a/libavcodec/h264_metadata_bsf.c
> +++ b/libavcodec/h264_metadata_bsf.c
> @@ -76,6 +76,7 @@ typedef struct H264MetadataContext {
>      int crop_bottom;
>  
>      const char *sei_user_data;
> +    int delete_user_data;
>  
>      int delete_filler;
>  
> @@ -361,6 +362,21 @@ static int h264_metadata_filter(AVBSFContext *bsf, AVPacket *pkt)
>          }
>      }
>  
> +    if (ctx->delete_user_data) {
> +        for (i = au->nb_units - 1; i >= 0; i--) {
> +            if (au->units[i].type == H264_NAL_SEI) {
> +                H264RawSEI *sei = au->units[i].content;
> +
> +                for (j = sei->payload_count - 1; j >= 0; j--) {
> +                    if (sei->payload[j].payload_type ==
> +                        H264_SEI_TYPE_USER_DATA_UNREGISTERED)
> +                        ff_cbs_h264_delete_sei_message(ctx->cbc, au,
> +                                                       &au->units[i], j);
> +                }
> +            }
> +        }
> +    }
> +
>      // Only insert the SEI in access units containing SPSs, and also
>      // unconditionally in the first access unit we ever see.
>      if (ctx->sei_user_data && (has_sps || !ctx->done_first_au)) {
> @@ -684,6 +700,9 @@ static const AVOption h264_metadata_options[] = {
>      { "sei_user_data", "Insert SEI user data (UUID+string)",
>          OFFSET(sei_user_data), AV_OPT_TYPE_STRING, { .str = NULL }, .flags = FLAGS },
>  
> +    { "delete_user_data", "Delete all SEI user data",
> +        OFFSET(delete_user_data), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, FLAGS},
> +
>      { "delete_filler", "Delete all filler (both NAL and SEI)",
>          OFFSET(delete_filler), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, FLAGS},
>  
> 

This approach is too general, because stripping everything includes notes which may be required to correctly decode the stream.  An option like this was suggested a while ago and rejected because of the old nonstandard libx264 streams which have decoding broken by it.

Can you explain your intended use-case?  Perhaps a delete option which takes a UUID argument and removes any SEI UDU matching it?

- Mark