MP4 synthesis failed. Please help me find out where I made a mistake

[f1748x]

ffmpeg -f image2 -loop 1 -r 15 -i ./1.png -i ./1.mp3 -pix_fmt yuv420p -s 320x240 -t 15 -vcodec libx264 w.mp4 -y

func ComplexFilterExample(testInputFile, music, testOutputFile string) *ffmpeg.Stream {
// ffmpeg.
png := ffmpeg.Input(testInputFile, ffmpeg.KwArgs{
"r": "15",
"loop": 1,
"f": "image2",
})
mp3 := ffmpeg.Input(music)
return ffmpeg.Concat([]*ffmpeg.Stream{
png,
mp3,
}).
Output(testOutputFile, ffmpeg.KwArgs{
"pix_fmt": "yuv420p",
"vcodec": "libx264",
"s": "320x240",
"t": "15",
}).
OverWriteOutput()
}