Trimming of video

I have not found a way in the docs on how to trim the video down to a portion of the original (e.g. from x milliseconds to y milliseconds).

Seems to me that I could implement by creating a custom MediaSource and supplying it to the transform method.

Am I on the right track here or is there an already built in way that I am currently missing?

[izzytwosheds]

Done and merged: https://github.com/linkedin/LiTr/pull/71

[grahamearley]

Made some more progress! Instead of making a custom decoder, I ended up adding new logic to the VideoTrackTranscoder’s resizeDecodedInputFrame() method.

This is the logic that method currently uses to render frames (see the file here):

decoder.releaseOutputFrame(tag, true);
renderer.renderFrame(null, frame.bufferInfo.presentationTimeUs * MILLISECONDS_IN_SECOND);

This logic assumes we want to render every frame in the video (the first line’s true parameter tells the decoder to render, and the second line performs the render). For trimming, there are frames we don’t want to render! I updated the logic to this:

long presentationTimeUs = frame.bufferInfo.presentationTimeUs;
boolean shouldRender = presentationTimeUs >= trimStartUs && presentationTimeUs <= trimEndUs;

decoder.releaseOutputFrame(tag, shouldRender);

if (shouldRender) {
    renderer.renderFrame(null, frame.bufferInfo.presentationTimeUs * MILLISECONDS_IN_SECOND);
}

And this gives us a precisely trimmed output!

I haven’t cleaned anything up into more presentable code, but maybe next week I’ll have some time to get a draft PR up. Right now, I’m hardcoding my trim start and end values in a few places, so I’ll need to make a single spot for those parameters to be set.