cad/opencascade: unbreak with ffmpeg 4.0

src/Image/Image_VideoRecorder.cxx:279:25: error: use of undeclared identifier 'CODEC_FLAG_GLOBAL_HEADER'

aCodecCtx->flags |= CODEC_FLAG_GLOBAL_HEADER;
                    ^

src/Image/Image_VideoRecorder.cxx:452:38: error: use of undeclared identifier 'AVFMT_RAWPICTURE'

if ((myAVContext->oformat->flags & AVFMT_RAWPICTURE) != 0
                                   ^

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