How to fix the difference between duration of ffmpeg input and output?

Question

I am trying to generate a video from a bunch of png images and audio using the command:

/usr/bin/ffmpeg -y -framerate 30 -pattern_type glob -i 'images/*.png' -i audio.wav -c:v libx264 -b:v 0 -crf 18 -g 300000 -pix_fmt yuv420p -shortest output.mp4

There are a total of 52 images with their FFprobe output as below:

Input #0, png_pipe, from 'images/0000000.png':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: png, rgb24(pc), 1200x1000, 25 tbr, 25 tbn, 25 tbc

And FFprobe output for audio.wav is:

Input #0, wav, from 'audio.wav':
  Metadata:
    encoder         : Lavf58.29.100
  Duration: 00:00:01.74, bitrate: 256 kb/s
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 16000 Hz, 1 channels, s16, 256 kb/s

At 30 fps, the length of output video should be 1.734s, but actually, it is 1.80s.

FFprobe output for final video:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
  Duration: 00:00:01.80, start: 0.000000, bitrate: 1627 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1200x1000, 1603 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 16000 Hz, mono, fltp, 74 kb/s (default)
    Metadata:
      handler_name    : SoundHandler

Can someone help me understand why is there a difference and how can I remove it?

My use case requires that the video is of the same length as that of audio otherwise it will cause issues. Any help will be appreciated.

Answer 1

What you can do is use -shortest to stop encoding once the shortest stream ends. This option needs to be given before the output file.