feat: experimental video preview generator in webm form

1 files changed, 74 insertions, 0 deletions

diff --git a/src/api/utils/PreviewUtil.js b/src/api/utils/PreviewUtil.js
new file mode 100644
index 0000000..bf3a480
--- /dev/null
+++ b/src/api/utils/PreviewUtil.js
@@ -0,0 +1,74 @@
+const ffmpeg = require('fluent-ffmpeg');
+const probe = require('ffmpeg-probe');
+
+const path = require('path');
+
+const noop = () => {};
+
+module.exports = async opts => {
+	const {
+		log = noop,
+
+		// general output options
+		quality = 2,
+		width,
+		height,
+		input,
+		output,
+
+		numFrames,
+		numFramesPercent = 0.05
+	} = opts;
+
+	const info = await probe(input);
+	// const numFramesTotal = parseInt(info.streams[0].nb_frames, 10);
+	const { avg_frame_rate: avgFrameRate, duration } = info.streams[0];
+	const [frames, time] = avgFrameRate.split('/').map(e => parseInt(e, 10));
+
+	const numFramesTotal = (frames / time) * duration;
+
+	let numFramesToCapture = numFrames || numFramesPercent * numFramesTotal;
+	numFramesToCapture = Math.max(1, Math.min(numFramesTotal, numFramesToCapture)) | 0;
+	const nthFrame = (numFramesTotal / numFramesToCapture) | 0;
+
+	const result = {
+		output,
+		numFrames: numFramesToCapture
+	};
+
+	await new Promise((resolve, reject) => {
+		let scale = null;
+
+		if (width && height) {
+			result.width = width | 0;
+			result.height = height | 0;
+			scale = `scale=${width}:${height}`;
+		} else if (width) {
+			result.width = width | 0;
+			result.height = ((info.height * width) / info.width) | 0;
+			scale = `scale=${width}:-1`;
+		} else if (height) {
+			result.height = height | 0;
+			result.width = ((info.width * height) / info.height) | 0;
+			scale = `scale=-1:${height}`;
+		} else {
+			result.width = info.width;
+			result.height = info.height;
+		}
+
+		const filter = [`select=not(mod(n\\,${nthFrame}))`, scale].filter(Boolean).join(',');
+
+		ffmpeg(input)
+			.outputOptions(['-vsync', 'vfr'])
+			.outputOptions(['-q:v', quality, '-vf', filter])
+			.outputOption('-an')
+			.outputFormat('webm')
+			.output(output)
+			.on('start', cmd => log && log({ cmd }))
+			.on('end', () => resolve())
+			.on('error', err => reject(err))
+			.run();
+	});
+
+	return result;
+};