FFmpeg - video with a PNG and a WAV as long as the WAV

[frenksisco]

Hi, I need to combine a single image and an audio file to get a video of the same duration as the audio. The reason is that the image is the waveform of the audio track and with this trick the playback bar of the videoplayer seems to follow the shape of the audio.
I'm perfectly capable of doing this with Premiere Pro but for convenience I'd like to do it with FFmpeg.

I tried but the video duration is always a few seconds longer than the audio. Always...
I used this script, what am I doing wrong?

ffmpeg -loop 1 -i 01.png -i 01.wav -c:v libx264 -pix_fmt yuv420p -tune stillimage -c:a aac -b:a 256k -shortest -y output.mp4

01.wav is 7 s 249 ms long, the video obtained with this script is 9 s 200 ms long..
I attach the files of my test

01.wav

[pandy]

I think this may solve your issue https://ffmpeg.org/ffmpeg-filters.html#amovie

I think explicitly specifying frame rate may improve overall behavior.

(not sure as i can only assume where is the issue - to small framerate + too long GOP may lead to such behavior)

[frenksisco]

I didn't understand how to use the information on that page. What should I use?

I've tried to add -framerate option but the result is still wrong

ffmpeg -loop 1 -framerate 50 -i 01.png -i 01.wav -c:v libx264 -pix_fmt yuv420p -tune stillimage -c:a aac -b:a 256k -shortest -y output.mp4

Meanwhile I found this but it still does not solve my problem
https://stackoverflow.com/questions/55800185/my-ffmpeg-output-always-add-extra-30s-of-...04507#55804507

[jagabo]

I didn't understand how to use the information on that page. What should I use?

I've tried to add -framerate option but the result is still wrong

ffmpeg -loop 1 -framerate 50 -i 01.png -i 01.wav -c:v libx264 -pix_fmt yuv420p -tune stillimage -c:a aac -b:a 256k -shortest -y output.mp4

Meanwhile I found this but it still does not solve my problem
https://stackoverflow.com/questions/55800185/my-ffmpeg-output-always-add-extra-30s-of-...04507#55804507

I was able to duplicate your problem. And using the information from that link I was able to fix it.

ffmpeg -loop 1 -i 01.png -i 01.wav -c:v libx264 -pix_fmt yuv420p -tune stillimage -c:a aac -b:a 256k -shortest -fflags +shortest -y output.mp4

[frenksisco]

Great! Yes problem solved! The video duration is 7 s 400 ms while the audio duration is 7 s 249 ms. I think they can't really be coincident because of the difference between audio samples and frames. Anyway I'm totally satisfied! Thank you very much!

[jagabo]

Yes, the default frame rate in ffmpeg is 25 fps. So the granularity of video is 40 ms. 7.4 seconds is exactly 185 frames at 25 fps.

[frenksisco]