<p>I am using java to create image files that I am converting to video using FFMPEG. I am creating the midi and audio simultaneously on reaper then using the duration of the notes on the midi file to create the number of frames I need. These are the durations of the different notes I have:</p>

<pre><code>306.1224966434529
612.2449932869058
1224.4899865738262
1836.734979860732
</code></pre>

<p>In order to get the frames I need I am using the formula (fps * duration) / 1000 then rounding down which results in:</p>

<pre><code>306.1224966434529 -&gt; 18 frames
612.2449932869058 -&gt; 36 frames
1224.4899865738262 -&gt; 72 frames
1836.734979860732 -&gt; 110 frames
</code></pre>

<p>When I combine the audio it gradually goes out of sync. I played around and realised that the 72 frames require 74 frames and the 110 frame notes require 112 frames.</p>

<p>I am not sure how to account for this. I need to be able to calculate the number of frames required ahead of time rather than creating them in real time.</p>

CC BY-SA 3.0
2017-09-14T21:52:46.743Z
Are you using a [drop frame](https://en.wikipedia.org/wiki/SMPTE_timecode?wprov=sfla1) or non-drop frame rate? Please share your full ffmpeg command.
Michael Liebman
CC BY-SA 3.0
2017-09-15T19:42:00.953Z
Thanks for responding. I am not explicitly using either so whatever the default is. I managed to get it working by increasing the frame rate. 180fps + gets a good degree of accuracy so I think the precision wasn't close enough after rounding.
Ryan McCauley
<video><ffmpeg><audio><framerate>
Trying to understand the delay converting a sequence of images to video
Ryan McCauley
# Trying to understand the delay converting a sequence of images to video

(Asked by: username_0 on 2017-09-14)

I am using java to create image files that I am converting to video using FFMPEG. I am creating the midi and audio simultaneously on reaper then using the duration of the notes on the midi file to create the number of frames I need. These are the durations of the different notes I have:
306.1224966434529
612.2449932869058
1224.4899865738262
1836.734979860732

In order to get the frames I need I am using the formula (fps * duration) / 1000 then rounding down which results in:
306.1224966434529 -> 18 frames
612.2449932869058 -> 36 frames
1224.4899865738262 -> 72 frames
1836.734979860732 -> 110 frames

When I combine the audio it gradually goes out of sync. I played around and realised that the 72 frames require 74 frames and the 110 frame notes require 112 frames.
I am not sure how to account for this. I need to be able to calculate the number of frames required ahead of time rather than creating them in real time.

**Tags:** video, ffmpeg, audio, framerate

> **Comments:**
> **username_1**: Are you using a [drop frame](https://en.wikipedia.org/wiki/SMPTE_timecode?wprov=sfla1) or non-drop frame rate? Please share your full ffmpeg command.  
> **username_0**: Thanks for responding. I am not explicitly using either so whatever the default is. I managed to get it working by increasing the frame rate. 180fps + gets a good degree of accuracy so I think the precision wasn't close enough after rounding.  

---

## 0 answers

