FFMPEG (libx264) "height not divisible by 2"

user_396077 0
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I am trying to encode a .mp4 video from a set of frames using FFMPEG using the libx264 codec.

This is the command I am running:

/usr/local/bin/ffmpeg -r 24 -i frame_%05d.jpg -vcodec libx264 -y -an video.mp4

I sometimes get the following error:

[libx264 @ 0xa3b85a0] height not divisible by 2 (520x369)

After searching around a bit it seems that the issue has something to do with the scaling algorithm and can be fixed by adding a -vf argument.

However, in my case I don't want to do any scaling. Ideally, I want to keep the dimensions exactly the same as the frames. Any advice? Is there some sort of aspect ratio that h264 enforces?

libx264 h.264 ffmpeg
7 Answers

The problem with the scale solutions here is that they distort the source image/video which is almost never what you want.

Instead, I've found the best solution is to add a 1-pixel pad to the odd dimension. (By default, the pading is black and hard to notice.)

The problem with the other pad solutions is that they do not generalize over arbitrary dimensions because they always pad.

This solution only adds a 1-pixel pad to height and/or width if they are odd:

-vf pad="width=ceil(iw/2)*2:height=ceil(ih/2)*2"

This is ideal because it always does the right thing even when no padding is necessary.

user_5112000

You may also use bitand function instead of trunc:

bitand(x, 65534)

will do the same as trunc(x/2)*2 and it is more transparent in my opinion.
(Consider 65534 a magical number here ;) )

My task was to scale automatically a lot of video files to half resolution.

scale=-2,ih/2 lead to slightly blurred images

reason:

  • input videos had their display aspect ratio (DAR) set
  • scale scales the real frame dimensions
  • during preview the new videos' sizes have to be corrected using DAR which in case of quite low-resoution video (360x288, DAR 16:9) may lead to blurring

solution:

-vf "scale='bitand(oh*dar, 65534)':'bitand(ih/2, 65534)', setsar=1"

explanation:

  • output_height = input_height / 2
  • output_width = output_height * original_display_aspect_ratio
  • both output_width and output_height are now rounded to nearest smaller number divisible by 2
  • setsar=1 means output_dimensions are now final, no aspect ratio correction should be applied

Someone might find this helpful.

user_54750450
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