MS Bot Framework - Messages with audio attachments lost

Question

I'm writing a bot in Node.js using the MS Bot Framework. To send attachments, I'm actually using the filestream buffer as the contentUrl, e.g.

...
var base64 = new Buffer(filedata).toString('base64');
var msg = new builder.Message()
    .setText(session, text)
    .addAttachment({
        contentUrl: util.format('data:%s;base64,%s', contentType, base64),
        contentType: contentType
});
session.send(msg);
...

where contentType is the proper mimetype for the file in question.

When I test this locally (using the Bot Framework Emulator), this works perfectly for both image and audio files - messages with image attachments display the image, and messages with audio attachments show the audiocard allowing for playback, etc.

However, when I test this through FB Messenger, the images work fine, but the audio messages just never appear in FB. Not even the text of the message comes through; it's like the entire message is lost. The dialogue simply skips over the message containing the audio attachment. I'm not even seeing any errors received server-side.

This is happening with both mp3 and wav test audio files, that are each under 1MB (smaller than many of the image files I've successfully tested).

Is there some trick to sending playable audio files to the FB Messenger channel specifically?

Thanks!

Answer 1

I wasn't (yet) able to get a response from FB support, but after further testing, it looks like there is a filesize limit on audio files FB Messenger will accept.

Specifically, I was able to get a sample file of ~45KB to send and display in Messenger successfully, but a larger file of ~400KB got dropped (aka seemed to send successfully from the server-side perspective, but did not show up in Messenger).

Strangely, some of my much larger image files went through, so it seems like this same limit does not exist for image attachments.

Will do some further testing, but it seems like the ultimate solution will be either to majorly compress my audio files, or to host them somewhere else instead of sending as a filestream.