Source → Route → Sink → Preview.
That's the whole API.

// LFile — from Example/Playout
#include "now2sdk.h"

LFile*    m_lFile    = new LFile();
LPreview* m_lPreview = new LPreview();

// Set props before play
m_lFile->setProps("loop", "true");
m_lFile->setProps("audio_gain", "85");
m_lFile->setProps("eof_hold", "true");

// Attach preview to Qt widget
m_lPreview->previewEnable(ui->playerPreview, true, true);
m_lPreview->previewObject(m_lFile);
m_lPreview->setProps("audio_meter", "true");

m_lFile->fileNameSet("/media/news_package.mp4");
m_lFile->play();

// Seek to 10 seconds
m_lFile->PosSet(10000.0);

// LLive — from Example/LiveDevice
#include "now2sdk.h"

LLive*    m_lLive    = new LLive();
LPreview* m_lPreview = new LPreview();

// Enable GPU decode & timecode
m_lLive->setProps("gpu", "true");
m_lLive->setProps("timecode", "true");

// Enumerate DeckLink cards
int count = 0;
m_lLive->DeviceGetCount(count);
m_lLive->DeviceSet(0);           // select first card
m_lLive->DeviceChannelSet(0);    // SDI input
m_lLive->DeviceFormatVideoSet(0); // 1080p50

// Attach preview
m_lPreview->previewEnable(ui->livePreview, true, true);
m_lPreview->previewObject(m_lLive);
m_lPreview->setProps("timecode.preview", "true");

m_lLive->Start();

// LRecorder — from Example/Recorder
#include "now2sdk.h"

LLive*     m_lLive     = new LLive();
LRecorder* m_lRecorder = new LRecorder();

// Configure output format
m_lRecorder->setContainer("mp4");
m_lRecorder->setVideoCodec("libx264");
m_lRecorder->setAudioCodec("aac");
m_lRecorder->setVideoBitrate(10000);  // 10 Mbps
m_lRecorder->setAudioBitrate(192);
m_lRecorder->setFilePath("/out/recording.mp4");

// Connect live source
m_lRecorder->recordObject(m_lLive);
m_lLive->Start();
m_lRecorder->Record();   // non-blocking

// Live stats
LRecorder::Stats stats;
m_lRecorder->getStats(stats);  // fileSizeBytes, fps...

// LMixer + LSwitcher — from Example/Switcher
#include "now2sdk.h"

LFile*     m_lFile1   = new LFile();
LFile*     m_lFile2   = new LFile();
LMixer*    m_lMixer   = new LMixer();

// Layer 0: full-screen base
m_lMixer->addLayer("base", m_lFile1, 0, 0, 0, 255, 1920, 1080);

// Layer 1: picture-in-picture
auto pip = m_lMixer->addLayer("pip", m_lFile2, 1, 1200, 100, 255, 640, 360);
pip->borderColor = "#FFFFFF";
pip->borderSize  = 5;

m_lFile1->play();
m_lFile2->play();