Duration changes with FPS

[Meldiron]

Using JSON below I tried many different renders to see how framerate changes video duration. I will try to find bug in code but I may need some help. Here are some tests:

Desired duration: 90 seconds without transition, 89 seconds with transition (2x 0.5s duration)

width (px)	height(px)	fps	output duration (sec)	output duration (with transition null)
400	400	10	88.700000	89.700000
400	400	20	88.850000	89.850000
400	400	30	88.900000	X
400	400	40	88.925000	X
400	400	50	88.940000	X
400	400	60	88.950000	89.950000
400	400	120	88.975000	X
400	400	240	88.988000	89.988000
------------	------------	-----	-----------------------	-----------------
800	800	10	88.700000	X
1920	1080	10	88.700000	X

(X means "no test")

JSON:

{ 
  "width": 1920, "height": 1080, "fps": 10,
  "outPath": "./subtitle.mp4",
  "defaults": {
    "layer": { "fontPath": "./Montserrat-Bold.ttf" },
    "transition": { "name": "fade" },
  },
  "clips": [
    { "duration": 30, "layers": [
       {
          "type": "subtitle",
          "text": "ST1 "
        },
         {
          "type": "title",
          "text": "T1 "
        }
    ] },
    { "duration": 30, "layers": [
       {
          "type": "subtitle",
          "text": "ST2 "
        },
         {
          "type": "title",
          "text": "T2 "
        }
    ] },
    { "duration": 30, "layers": [
       {
          "type": "subtitle",
          "text": "ST3 "
        },
         {
          "type": "title",
          "text": "T3 "
        }
    ] },
  ],
}

[mifi]

Yeah, I think there is a small bug where it drops a frame some times. Will look into it when I have more time

[ghost]

@mifi Can confirm when using fps: 60

[timosg]

Can also confirm when using fps: 15 and fps: 30 on my videos -> expected duration 18:17 -> output duration 18:15

[ghost]

@mifi I have two videos, both are 1.5 seconds, 60 fps. I do a 3-second transition so it should be as flush 3-sec output. Instead, the output is 2.21667s. When I change the FPS to 15, the output becomes 2.2s.

Edit: My understanding of how transitions work was wrong, the output should be 1.5 seconds, as the transition happens while both videos are playing. I was thinking in terms of addition due to the fact I was working with images.

It's causing my video and audio to be out of sync in proportion to the number of transitions. I tried commenting out the pts factor and scaling stuff in videoFrameSource.js and it made no difference though.

[ghost]

@TimoGruber For now I am using ffmpeg-gl-transitions since gl transitions were the only component of editly I was using

[mifi]

Can you try again in 0.5.0?

[timosg]

For me there is still a slight difference on the output file (about 1 sec). But with the keepSourceAudio option there is obviously no need for creating a external audio file from the sources and sync it with the video.