[FFmpeg-user] Fwd: Generate video remains blocked

[local host]

Hello,

I want to concatenate 3 videos with a fade between the last two videos.
However, the generation remains stuck to X frames.

Here is the command used:
ffmpeg -i "firstClip.mp4" -i "secondClip.mp4" -i "thirdClip.mp4" -y
-filter_complex
"[1:v]trim=start=0:end=3,setpts=PTS-STARTPTS[1_clip_1];
[1:v]trim=start=3:end=6,setpts=PTS-STARTPTS[fadeoutsrc_1];
[fadeoutsrc_1]format=pix_fmts=yuva420p,fade=t=out:st=0:d=1:alpha=1[fadeout_1];
[fadeout_1]fifo[fadeoutfifo_1];[2:v]trim=start=3,setpts=PTS-STARTPTS[2_clip_2];
[2:v]trim=start=0:end=3,setpts=PTS-STARTPTS[fadeinsrc_2];
[fadeinsrc_2]format=pix_fmts=yuva420p,fade=t=in:st=0:d=1:alpha=1[fadein_2];
[fadein_2]fifo[fadeinfifo_2];
[fadeoutfifo_1][fadeinfifo_2]overlay[crossfade_2];
[0:v][1_clip_1][crossfade_2][2_clip_2]concat=n=4[output];
[1:a][2:a]
acrossfade=d=1[audioTmp];[0:a][audioTmp]concat=n=2:v=0:a=1[audio]"
-vcodec h264 -map [output] -map [audio] output.mp4

Thanks for your help.