[FFmpeg-trac] #9156(avutil:new): Option flag usage

[FFmpeg]

#9156: Option flag usage
--------------------------------+---------------------------------------
             Reporter:  sceedy  |                     Type:  defect
               Status:  new     |                 Priority:  minor
            Component:  avutil  |                  Version:  unspecified
             Keywords:          |               Blocked By:
             Blocking:          |  Reproduced by developer:  0
Analyzed by developer:  0       |
--------------------------------+---------------------------------------
 I have either badly misunderstood or I have found a fault.

 I am using the public API. I have looked at the AVOption referenced by
 several examples of AVClass with particular interest in
 { x , x ,  x , AV_OPT_TYPE_CONST, x ,  x , x , ENC, x }
 (where x = don’t care) as this is how I believe options for bit encoded
 flags are stored. In all the cases I have looked at the flag settings are
 not mutually exclusive e.g. class "mpegts_muxer_class" flags "latm" and
 "system_b". I tried code like
  Options = NULL;
  av_dict_set(&Options,"mpegts_flags","system_b",0);
  av_dict_set(&Options,"mpegts_flags","latm", AV_DICT_DONT_OVERWRITE);
 ReturnCode = avformat_write_header(OutputContext,&Options);
 All that happened was the last flag setting in the list won. I then looked
 at opt.c and found flags are set in function "write_number"
 ...
     case AV_OPT_TYPE_BOOL:
     case AV_OPT_TYPE_FLAGS:
     case AV_OPT_TYPE_INT:
         *(int *)dst = llrint(num / den) * intnum;
         break;
 ...
 For flags to work the way I expect, i.e. you can "or" multiple values, I
 believe this should read
 ...
     case AV_OPT_TYPE_BOOL:
     case AV_OPT_TYPE_INT:
         *(int *)dst = llrint(num / den) * intnum;
         break;
     case AV_OPT_TYPE_FLAGS:
         *(int *)dst |= llrint(num / den) * intnum;
         break;
 ...

 As a work around I use av_opt_ptr to get the address of the *flags*
 variable and av_dict_get to get the values, "or" them together myself and
 then write them to the address using the pointer.

 So the question I wish answered is have I fundamentally misunderstood the
 way bit flags are set in options or have I found a problem?

--
Ticket URL: <https://trac.ffmpeg.org/ticket/9156>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker