Node-fluent-ffmpeg: Piping frames

[timkendall]

Does .pipe() return a full frame in each buffer? Trying to send video stream directly from fluent-ffmpeg to node-opencv for analysis.

[njoyard]

No it doesn't. Buffer size mostly depends on OS configuration. You'll get chunks of a video file that have no direct link whatsoever with the video timeline.

[timkendall]

Ah alright, kinda figured that. Any suggestions on how to implement something like this?

[njoyard]

I think you may simply run ffmpeg with something like "frame%d.jpg" as the output filename. ffmpeg will automatically select the jpeg format and output frame0.jpg, frame1.jpg, etc.

Then you can use the 'progress' event from fluent-ffmpeg ; the 'frames' attribute in the argument to the event handler will tell you how many frames ffmpeg has processed yet, thus how many output files are available. Here's a quick example:

function enqueueFrame(number) {
  // do something with frame<number>.jpg
}

var lastFrameEnqueued = 0;
ffmpeg(inputStream)
  .on('progress', function(progress) {
    var n = lastFrameEnqueued + 1;
    lastFrameEnqueued = progress.frames - 1;
    for (; n < progress.frames; n++) {
       enqueueFrame(n);
    }
  })
  .save('frame%d.jpg')

[njoyard]

Oh, and you may want to check whether progress.frames is a valid number. I think the first occurences of the 'progress' may have an empty string there instead (while ffmpeg is getting set up).

[timkendall]

Thanks yeah that works, a little laggy because frames have to be saved and then read from disk but not bad.

[njoyard]

Save them in /tmp, most distros mount /tmp on a ramdisk nowadays, that way it will be just as fast as using plain in-memory streams.

(edit: typo)

[njoyard]

Closing for housekeeping, feel free to reopen if necessary !