multimedia/tvheadend: unbreak with ffmpeg 4.0

src/muxer/muxer_libav.c:177:17: error: use of undeclared identifier 'CODEC_FLAG_GLOBAL_HEADER'

c->flags |= CODEC_FLAG_GLOBAL_HEADER;
            ^

src/plumbing/transcoding.c:22:10: fatal error: 'libavfilter/avfiltergraph.h' file not found

^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

src/plumbing/transcoding.c:576:29: error: use of undeclared identifier 'CODEC_FLAG_GLOBAL_HEADER'

octx->flags          |= CODEC_FLAG_GLOBAL_HEADER;
                        ^

src/plumbing/transcoding.c:621:22: error: use of undeclared identifier 'CODEC_FLAG_BITEXACT'

octx->flags |= CODEC_FLAG_BITEXACT;
               ^

src/plumbing/transcoding.c:632:24: error: use of undeclared identifier 'CODEC_FLAG_QSCALE'

octx->flags |= CODEC_FLAG_QSCALE;
               ^

src/plumbing/transcoding.c:635:24: error: use of undeclared identifier 'CODEC_FLAG_QSCALE'

octx->flags |= CODEC_FLAG_QSCALE;
               ^

src/plumbing/transcoding.c:1291:30: error: use of undeclared identifier 'CODEC_FLAG_GLOBAL_HEADER'

octx->flags         |= CODEC_FLAG_GLOBAL_HEADER;
                       ^

src/plumbing/transcoding.c:1296:33: error: use of undeclared identifier 'CODEC_FLAG_QSCALE'

octx->flags          |= CODEC_FLAG_QSCALE;
                        ^

src/plumbing/transcoding.c:1342:30: error: use of undeclared identifier 'CODEC_FLAG_GLOBAL_HEADER'

octx->flags         |= CODEC_FLAG_GLOBAL_HEADER;
                       ^

src/plumbing/transcoding.c:1373:30: error: use of undeclared identifier 'CODEC_FLAG_GLOBAL_HEADER'

octx->flags         |= CODEC_FLAG_GLOBAL_HEADER;
                       ^

src/plumbing/transcoding.c:2179:29: error: use of undeclared identifier 'CODEC_CAP_EXPERIMENTAL'

if (((p->capabilities & CODEC_CAP_EXPERIMENTAL) && !experimental) ||
                        ^

src/plumbing/transcoding.c:2194:33: error: use of undeclared identifier 'CODEC_CAP_EXPERIMENTAL'

(p->capabilities & CODEC_CAP_EXPERIMENTAL) ?
                   ^

PR: 227726
Reported by: antoine (via exp-run)
Obtained from: upstream