[FFmpeg-devel] [PATCH v11 3/4] avfilter/vf_showinfo: display H.26[45] user data unregistered sei message

[lance.lmwang at gmail.com]

On Thu, Jun 11, 2020 at 05:44:45PM +0200, Andreas Rheinhardt wrote:
> lance.lmwang at gmail.com:
> > On Wed, Jun 10, 2020 at 08:13:59PM +0200, Andreas Rheinhardt wrote:
> >> lance.lmwang at gmail.com:
> >>> From: Limin Wang <lance.lmwang at gmail.com>
> >>>
> >>> Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
> >>> ---
> >>>  libavfilter/vf_showinfo.c | 37 +++++++++++++++++++++++++++++++++++++
> >>>  1 file changed, 37 insertions(+)
> >>>
> >>> diff --git a/libavfilter/vf_showinfo.c b/libavfilter/vf_showinfo.c
> >>> index 5d4aee4..2511da5 100644
> >>> --- a/libavfilter/vf_showinfo.c
> >>> +++ b/libavfilter/vf_showinfo.c
> >>> @@ -37,6 +37,7 @@
> >>>  #include "libavutil/timecode.h"
> >>>  #include "libavutil/mastering_display_metadata.h"
> >>>  #include "libavutil/video_enc_params.h"
> >>> +#include "libavutil/avstring.h"
> >>>  
> >>>  #include "avfilter.h"
> >>>  #include "internal.h"
> >>> @@ -190,6 +191,39 @@ static void dump_video_enc_params(AVFilterContext *ctx, AVFrameSideData *sd)
> >>>          av_log(ctx, AV_LOG_INFO, "%u blocks; ", par->nb_blocks);
> >>>  }
> >>>  
> >>> +static int string_is_print(const uint8_t *str)
> >>> +{
> >>> +    while (av_isgraph(*str)) str++;
> >>> +    return !*str;
> >>
> >> This is dangerous: The SEI message needn't be zero-terminated, so this
> >> may segfault. Furthermore, it is also wrong: If the user data payload
> >> happens to contain a binary zero preceded by printable ASCII characters,
> >> it will be considered a string, even if there are unprintable characters
> >> after the binary zero (which may really happen if the payload is
> >> actually binary).
> > 
> > Give below test example, if a binary zero preceded by "hello", the %s will print
> > out "hello" and ignore the other unprintable characters. I think it's expected.
> > We only dump the printable result if it is string or parial string.
> > 
> >      unsigned char test[10];
> > 
> >      test[0] = 'h';
> >      test[1] = 'e';
> >      test[2] = 'l';
> >      test[3] = 'l';
> >      test[4] = 'o';
> >      test[5] = 0;
> >      test[6] = 133;
> >      test[7] = 144;
> > 
> >      printf( "test: %s \n", test);
> > 
> > So I thbink it's safety after add one padding zero bytes for the user data
> > buffer.
> > 
> 
> And who says that what is before the first binary zero is actually a
> string and not some actually binary data that just happens to be in the
> printable ASCII range and will be gibberish when printed?

Sorry, it seems that I misunderstand your comments at first, I have change to check
whether *str is 0, please help to check whether my update patch solve your question.

> 
> >>
> >>> +}
> >>> +
> >>> +static void dump_sei_unregistered_metadata(AVFilterContext *ctx, AVFrameSideData *sd)
> >>> +{
> >>> +    const int uuid_size = 16;
> >>> +    uint8_t *user_data = sd->data;
> >>> +
> >>> +    if (sd->size < uuid_size) {
> >>> +        av_log(ctx, AV_LOG_ERROR, "invalid data(%d < UUID(%d-bytes))", sd->size, uuid_size);
> >>> +        return;
> >>> +    }
> >>> +
> >>> +    av_log(ctx, AV_LOG_INFO, "User Data Unregistered:\n");
> >>> +    av_log(ctx, AV_LOG_INFO, "UUID=");
> >>> +    for (int i = 0; i < uuid_size; i++) {
> >>> +        av_log(ctx, AV_LOG_INFO, "%02x", user_data[i]);
> >>> +        if (i == 3 || i == 5 || i == 7 || i == 9)
> >>> +            av_log(ctx, AV_LOG_INFO, "-");
> >>> +    }
> >>> +    av_log(ctx, AV_LOG_INFO, "\n");
> >>> +
> >>> +    user_data += uuid_size;
> >>> +    /* Only print the user data details if it's string */
> >>> +    if (string_is_print(user_data)) {
> >>> +        av_log(ctx, AV_LOG_INFO, "User Data=");
> >>> +        av_log(ctx, AV_LOG_INFO, "%s", user_data);
> >>
> >> Given that the user_data needn't be zero-terminated, you must specify
> >> the precision (i.e. the number of bytes to write) here.
> >>
> >>> +    }
> >>> +}
> >>> +
> >>>  static void dump_color_property(AVFilterContext *ctx, AVFrame *frame)
> >>>  {
> >>>      const char *color_range_str     = av_color_range_name(frame->color_range);
> >>> @@ -375,6 +409,9 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
> >>>          case AV_FRAME_DATA_VIDEO_ENC_PARAMS:
> >>>              dump_video_enc_params(ctx, sd);
> >>>              break;
> >>> +        case AV_FRAME_DATA_SEI_UNREGISTERED:
> >>> +            dump_sei_unregistered_metadata(ctx, sd);
> >>> +            break;
> >>>          default:
> >>>              av_log(ctx, AV_LOG_WARNING, "unknown side data type %d (%d bytes)",
> >>>                     sd->type, sd->size);
> >>>
> >>
> >> _______________________________________________
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> >>
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> > 
> 
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-- 
Thanks,
Limin Wang