S3 Video to audio file convert using Node js (Lambda function) - node.js

Question

I am trying to convert S3 video file to audio file through Lambda function. Whenever video files are uploaded into an S3 bucket I have to generate an audio file and save it back to S3 bucket by triggering the AWS Lambda function. I can convert the video file to audio in local. ( Convert video to an audio file using FFMPEG). But I am wondering, how to do this conversion part in Lambda function every time the video file is uploaded into an S3 bucket. I have no idea how to do this AWS Lambda function. Please share your suggestions.
Sample code:
var ffmpeg = require('fluent-ffmpeg');
/**
* input - string, path of input file
* output - string, path of output file
* callback - function, node-style callback fn (error, result)
*/
function convert(input, output, callback) {
ffmpeg(input)
.output(output)
.on('end', function() {
console.log('conversion ended');
callback(null);
}).on('error', function(err){
console.log('error: ', e.code, e.msg);
callback(err);
}).run();
}
convert('./df.mp4', './output.mp3', function(err){
if(!err) {
console.log('conversion complete');
//...
}
});
Thanks,

Answer 1

You just need to set up an event on s3 bucket - put object - to trigger lambda function (you will get access to the description of the object uploaded to that S3 bucket through the first parameter of the lambda function).
If you can convert the video file to audio on your local machine, using some external libraries, then you need to create a zip file containing your lambda function (in the root of the zip file) as well as the dependencies.
This is pretty simple in case of Node. Create a new folder, run npm init, install needed modules, create index.js file where you put your Node code. Zip all the contents of this folder (not the folder itself). When you create new lambda function, choose to upload this zip file.
If you are wondering about how to programatically communicate with AWS resources and manipulate them, then check aws-sdk which you can import as a module and use it for that purpose.
So basically what you will need to inside of your lambda function is to parse event argument (the first parameter) to obtain bucket and key of the uploaded object. Then you will call s3.getObject method to get the data. Process the data with your custom logic. Call s3.putObject to store the newly transformed data to new S3 location.
Lambda has access to its own local file system, if your code needs to store some data there. You just need to specify absolute path to the file, such as /tmp/output.mp3. To retrieve it, you can use fs module. Then, you can continue with s3.putObject.