0
$\begingroup$

I have rendered an image sequence from my animation, with FPS 30. Now, while making the video from that particular image sequence, can I use a different FPS, say 24 ?

Technically it is possible, I have checked with a small test video. But my doubt is, does it make any difference in the video quality inherently ?

Let me assume that the answer to the above question is NO (which also seems logical to me since each png file is complete on its own and they can be viewed at any speed). But then the question that comes to my mind is, why do we have the frame rate settings at all while rendering as an image sequence ? It seems more logical to display frame rate settings only during the video rendering, and disable it during image rendering since it remains meaningless in that case. Or is there any other purpose of setting the frame rate during the image render ?

I have checked some similar questions on this topic but did not get a complete answer to my original question + the doubt above. Hence I am posting it as a new question. Any suggestion from experts will be highly appreciated.

Improve this question
$\endgroup$

3 Answers 3

Reset to default
0
$\begingroup$

To my knowledge using another frame rate while rendering an image sequence will ,without changing anything else, change the quality of the output video because a different number of the images out of the sequence will be shown in the output video per second. But the other more noticeable effect would be that by packing a different number of frames in each second you would effectively speed up/ slow down the output video.

It is possible to correct for that speed up in the strip options under time, but you run into another issue: While the video is paused it makes no difference in quality, but if the rendered frame rate of the image sequence is not a multiple of the the new frame rate it can lead to glittery motion. This happens because blender sometimes would need frames that lay between the given frames in the images sequence. Because that is not possible it has to decide for one of those frames. The distance between the chosen frames can vary, sometimes be 1, sometimes be 2, so in the rendered video the motion seems to jump.

so most of the time it makes sense to stick to one frame rate from start to finish.

For why the frame rate needs to be able to be changed even if you render an Image Sequence:
One simple reason is that the viewport animation works with the same frame rate so to change that you need that option exposed.

Does that answer your questions? I hope my explanation makes sense.

Improve this answer
$\endgroup$
2
  • $\begingroup$ Thanks for taking your time to answer. Did you make a typo in your first sentence where you wanted to say that there won't be any change in quality ? I am not sure. Anyway, I think you correctly pointed out that the video will speed up/ slow down, which is obvious... but I was referring to the display quality. I understood your answer. I will accept it if no better or no more detailed answer is posted. Thanks once again for helping me out. You are awesome! $\endgroup$
    – Jeet GT
    Commented Aug 26, 2020 at 5:13
  • $\begingroup$ If all you are refering to with quality is the quality of the images then yes, the quality doesnt change. But the quality of the final video will change, because there are more factors to video quality than singe image quality. Thats what i mean in the first sentence. I hope that makes things more clear. $\endgroup$
    – leonkax
    Commented Aug 26, 2020 at 10:55
0
$\begingroup$

The fps in image sequence rendering is perfectly reasonable: it tells blender how many frames to be rendered in every single second of the animations. The speed of the animation is sothing you can control, but you won't change it after you choose an initial setting.

Let's take into consideration a video of a man that walks: 2 steps should last 1 seconds: if you render 100 fps and 1 second of animation (100 images) you'll have 1 step.

If you later change the fps (let's say 30 fps), you'll have again the same 1 step, but with a less smooth frame rate.

Improve this answer
$\endgroup$
2
  • $\begingroup$ Some reference in changing the frame rate of a video with ffmpeg: superuser.com/questions/843292/… trac.ffmpeg.org/wiki/ChangingFrameRate $\endgroup$
    – Sanbaldo
    Commented Apr 12, 2021 at 5:47
  • $\begingroup$ When we render a scene in Blender, we explicitly mention the start frame number and end frame number, effectively telling Blender how many frames to be generated. We don't enter length of the output in seconds. So FPS makes no sense here (for image sequence output). Had it been the case that we mention the length of the animation for image sequence output, FPS would have been meaningful and mandatory. But we mention exact number of frames to be generated. So, I am still not sure what purpose is being met by entering FPS in image sequence output. $\endgroup$
    – Jeet GT
    Commented Apr 16, 2021 at 6:34
0
$\begingroup$

An image sequence is just a collection of consecutive images, each image being a still frame. FPS only matters for playback and for videos. Since Blender can play animations no matter if "live" in viewport or from rendered video or image sequence, this information is used for playback. (I guess that's why you find it in the Dimensions settings rather than the Output settings.)

In a video file, the framerate determines what speed is "normal" to play the video. Still images are not tied to a certain framerate. So if you render an image sequence with let's say 240 frames at 30 fps, then this would be 8 seconds if you play it at 30 fps.

But it's simply 240 frames. If you make a video out of it with 24 fps, the video will last 10 seconds. That's how my digital camera makes slow-motion videos. It records at 120 fps but puts them into a video file set to 30 fps - this makes the footage look like 4 times slower. If I make an image sequence out of the individual frames and make a 120 fps video out of it, the speed of the footage would look absolutely normal.

The only problem you might experience is that your animation will be a bit slower than you expect/need it to be, if you stretch those 8 to 10 seconds. If you want to keep it at 8 seconds, you have to scale the sequence in the Video Editor or cut out single frames to reduce the 240 to 192 frames. In both cases I suspect the animation wouldn't look as smooth as before.

Improve this answer
$\endgroup$
8
  • $\begingroup$ Thanks! This perfectly explains the result of FPS change. Yes, changing the FPS during video render will make the video faster or slower. However, my doubt was, why there is a frame-rate setting when rendering an image sequence. FPS makes no sense when all we want is a bunch of still images, and we explicitly also mention the start frame number and end frame number, effectively telling Blender how many frames to be generated. We don't enter length of the output in seconds. So FPS makes no sense here (for image sequence output). Or maybe I am still missing something. $\endgroup$
    – Jeet GT
    Commented Apr 16, 2021 at 6:32
  • $\begingroup$ As I said in my first paragraph, there might be a reason why you find the FPS setting in the Dimensions settings and not in the Output settings. They are used for playback and preview and Blender uses them to play the animated image sequence after you rendered it if you hit Ctrl + 11. Let's say you're making a movie at 24 fps. If you animated a character too fast or slow to look right at 24 fps, changing playback in Blender won't help your movie - and dropping or stretching frames makes it worse and movement no longer smooth. $\endgroup$
    – Gordon Brinkmann
    Commented Apr 16, 2021 at 8:26
  • $\begingroup$ Thanks! I get you. So this FPS is in relation to the viewport or playback, not in relation to the actual output files in an image sequence. That makes sense. However, the dimensions themselves (Resolution, Aspect, Frame Start, Frame End) impact the output image sequence very much. Surprisingly, the FPS is bundled with these fields, but it is irrelevant for the output image sequence. I still believe, there is enough scopes for someone to get confused, and there can be a better place to keep the FPS. This may be a UI issue, but your answer helped me to understand what is going behind the scene. $\endgroup$
    – Jeet GT
    Commented Apr 18, 2021 at 6:43
  • $\begingroup$ But image files are, no matter what they show, just single files containing still images that have no actual connection to each other. If you rid the names of the consecutive increments Blender wouldn't know how to play them when hitting Ctrl+F11. Even if you have image0001 to image0100, but image0050 is missing, playback stops (or restarts) after image0049. On the other hand you can take 100 random images that show completely different things, if you name them image0001 to image0100, Blender will play them as a sequence when you hit Ctrl+F11 and with the FPS you've set. $\endgroup$
    – Gordon Brinkmann
    Commented Apr 18, 2021 at 10:15
  • $\begingroup$ Or if you take said image sequence where image0050.png is missing. Get ANY other png image, rename it to image0050.png and Blender will play the sequence up to frame 100 again, just showing that other frame on position 50. Even if the new frame has a different, maybe bigger size or aspect ratio, Blender will show it cropped to the settings. I think your confusion may arouse because of a misconception of image sequences. In the end they are timeless still images. If you look at them for the blink of an eye or an hour, they don't change. They are not animated. $\endgroup$
    – Gordon Brinkmann
    Commented Apr 18, 2021 at 10:25

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .