frame-converter.js

/*
 * Authored by Runpeng Liu,
 * Brain Power (2018)
 */

const TMP_DIR = process.env.local ? "./tmp" : "/tmp"; // The temp directory to write the image frames to before video conversion. On AWS Lambda, this must be `/tmp`
const PAD_LENGTH = 3;
const MKV_FILE_EXT = ".mkv";
const ffmpeg = require('./lib/ffmpeg');
const path = require("path");
const fs = require("fs");

exports.convertFramesToMKVFragment = (frameDataArray, params) => {
    const RANDOM_KEY = Math.floor(10 ** 8 * Math.random()).toString();
    const FRAME_PREFIX = `${RANDOM_KEY}-frame-`;
    return new Promise((resolve, reject) => {
        const fileWritePromises = frameDataArray.filter((frameData) => {
            // Get rid of empty frames.
            return !!frameData;
        }).map((frameData, index) => {
            // Strip off the data:url prefix to get just the base64-encoded bytes.
            const data = frameData.replace(/^data:image\/\w+;base64,/, "");
            const buf = new Buffer(data, 'base64');
            return new Promise((resolve, reject) => {
                // For padding filenames of image frames
                const pad = (number, size) => {
                    let s = String(number);
                    while (s.length < (size || 2)) { s = `0${s}`; }
                    return s;
                };
                const filename = path.join(TMP_DIR, `${FRAME_PREFIX + pad(index, PAD_LENGTH)}.jpg`);
                // e.g. frames will be written to /tmp/XXXXX-frame-000.jpg, /tmp/XXXXX-frame-001.jpg, ...
                fs.writeFile(filename, buf, err => {
                    if (err) reject(err);
                    else resolve(filename);
                });
            });
        });
        Promise.all(fileWritePromises).then(persistedFrames => {
            // Output filename of streamable MKV fragment.
            const outputFilename = `_${new Date().getTime()}${MKV_FILE_EXT}`;
            // Temp write location of MKV fragment.
            const outputFileLocation = path.resolve(path.join(TMP_DIR, outputFilename));
            const success = () => {
                resolve({
                    outputFileLocation,
                    outputFilename,
                    persistedFrames
                });
            };
            // FFMPEG_CMD for converting sequence of image frames to streamable video fragment
            // Can be modified at deploy-time by editing the CloudFormation stack parameters or at run-time by changing Lambda function environment variable.
            // Currently, this is the command being used: `ffmpeg -r %r -f image2 -s 640x480 -i %i -vcodec libx264 -crf 25 -pix_fmt yuv420p %o`
            // -r specifies the frame rate
            // -s specifies the output resolution
            // -i specifies the sequence of input frames using wildcard filepath notation
            //    e.g. 'XXXXX-frame-%03d.jpg' searches for filenames padded to 3 digits: 'XXXXX-frame-000.jpg', 'XXXXX-frame-001.jpg', etc.
            // -o specifies the output filepath
            // -vcodec specifies the video encoding; must be libx264 to compatible with Kinesis Video Stream
            // -crf specifies the compression quality - 0 is perfectly lossless (unrecommended; very slow); 100 is very lossy.
            let ffmpegCmd = (process.env.FFMPEG_CMD)
                .replace("%o", outputFileLocation)
                .replace("%r", process.env.TARGET_FRAME_RATE || 10)
                .replace("%i", path.resolve(path.join(TMP_DIR, `${FRAME_PREFIX}%0${PAD_LENGTH.toString()}d.jpg`)));
            
            ffmpeg(ffmpegCmd)
                .then(success)
                .catch(err => {
                    console.error(err);
                    reject(err);
                });
        }).catch(err => {
            console.log(err);
            reject(err);
        });
    });
}