H.264 render of 24fps reverts to 30fps in output

Question

Hi, I'm new to After Effects and pretty new to video editing overall. I've run into a strange problem that I cannot solve or find answers to.

I created a blank 1920x1080 24 fps composition, 30 seconds long. I imported a single png image (no footage) and used two start/end keyframes to have it pan across the screen. Very basic, simple composition.

I exported to Media Encoder, used H.264 and rendered as mp4. Match Source, high bitrate. I verified that the frame rate is set to 24 fps. I even did this twice, once with "Match Source" and once with unchecking that box and manually setting the 24 fps.

Result: I get a clip that is 30 seconds long as it should be, but all the frames from After Effects are finished after 24 seconds and it's just black after that. Also, the file's metadata shows 30 fps. So, it seems that the 720 frames get interpreted as 30 frames per second instead of 24, which ruins the timing. If I change the composition and export to 30 fps then the frame timing is correct. Why is the export "stuck" at 30 fps interpretation regardless of my setting configuration? This error does not occur in .mov or .avi formats, which I checked.

Obviously I can use the other formats to work around this problem, so I'm not in a jam, but this startling failure with such a basic function led me to question whether I've grossly overlooked something important.

Note: I'm in Windows 10, AE 17.1.0.

Rick Gerard · Answer

This kind of problem is almost always user error. Without workflow details, it's impossible to tell. My first guess, custom render settings along with custom comp settings.

Changing the frame rate in the render settings of the Media Encoder or the Render settings in After Effects will not change the timing. It has never worked that way. Keyframes are based on time, not on frames. Create a comp that is 10 seconds long and 1 frame per second, animate the position of a layer from the left side of the comp to the right side so it takes 10 seconds, and you'll get 10 different positions for the layer one second apart.

Create another 10-second comp that is 10 seconds long but the frame rate is set to 30 frames per second and then add the first comp to the second comp and the position of the layer will now change 30 times a second and the layer will move smoothly across the screen.

The only way to foul up the interpretation in the comp or the render cue is to go to the comp settings and select preserve frame rate when nested or in the Render Cue.

The adobe media encoder does not do as good a job interpreting between frames if you force a different frame rate, but the length of the video and the playback speed will not change. The only way to change the timing of a video is to change the interpreted frame rate of the video. Change the 24-second video's frame rate to 30 fps using interpret footage and the speed will match.

I don't know of any rendering bug with the AME and I can't reproduce your error unless I change the timing of the keyframes in a comp.

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