How do I compose three overlapping videos w/audio in ffmpeg? - ffmpeg

Question

I have three videos: let's call them intro, recording and outro. My ultimate goal is to stitch them together like so:
Both intro and outro have alpha (prores 4444) and a "wipe" to transition, so when overlaying, they must be on top of the recording. The recording is h264, and ultimately I'm encoding out for youtube with these recommended settings.
I've figured out how to make the thing work correctly for intro + recording:
$ ffmpeg \
-i intro.mov \
-i recording.mp4 \
-filter_complex \
"[1:v]tpad=start_duration=10:start_mode=add:color=black[rv]; \
[1:a]adelay=delays=10s:all=1[ra]; \
[rv][0:v]overlay[v];[0:a][ra]amix[a]" \
-map "[a]" -map "[v]" \
-movflags faststart -c:v libx264 -profile:v high -bf 2 -g 30 -crf 18 -pix_fmt yuv420p \
out.mp4 -y
However I can't use the tpad trick for the outro because it would render black frames over everything.
I've tried various iterations with setpts/asetpts as well as passing -itsoffset for the input, but haven't come up with a solution that works correctly for both video and audio. This tries to start the outro at 16 seconds into the recording (10s start + 16s of recording is how I got to setpts=PTS+26/TB). del, but doesn't work correctly, I get both intro and outro audio from the first frame, and the recording audio cuts out when the outro overlay begins:
$ ffmpeg \
-i intro.mov \
-i recording.mp4 \
-i outro.mov \
-filter_complex \
"[1:v]tpad=start_duration=10:start_mode=add:color=black[rv]; \
[1:a]adelay=delays=10s:all=1[ra]; \
[2:v]setpts=PTS+26/TB[outv]; \
[2:a]asetpts=PTS+26/TB[outa]; \
[rv][0:v]overlay[v4]; \
[0:a][ra]amix[a4]; \
[v4][outv]overlay[v]; \
[a4][outa]amix[a]" \
-map "[a]" -map "[v]" \
-movflags faststart -c:v libx264 -profile:v high -bf 2 -g 30 -crf 18 -pix_fmt yuv420p \
out.mp4 -y
I think the right solution lies in the direction of using setpts correctly but I haven't been able to wrap my brain fully around it. Or, maybe I'm making life complicated and there's an easier approach?
In the nice-to-have realm, I'd love to be able to specify the start of the outro relative to the end of the recording. I will be doing this to a bunch of recordings of varying lengths. It would be nice to have one command to invoke on everything rather than figuring out a specific timestamp for each one.
Thank you!

Answer 1

Use adelay for all audio adjustments. Perform all mixing in a single amix.
Set the outro overlay to start only at the correct timestamps.
Use
$ ffmpeg \
-i intro.mov \
-i recording.mp4 \
-i outro.mov \
-filter_complex \
"[1:v]tpad=start_duration=10:start_mode=add:color=black[mainv]; \
[1:a]adelay=delays=10s:all=1[maina]; \
[2:v]setpts=PTS+26/TB[outv]; \
[2:a]adelay=delays=26s:all=1[outa]; \
[mainv][0:v]overlay=eof_action=pass[previd]; \
[previd][outv]overlay=enable='gte(t,26)'[v]; \
[maina][0:a][outa]amix=inputs=3[a]; \
-map "[v]" -map "[a]" \
-c:v libx264 -profile:v high -bf 2 -g 30 -crf 18 -pix_fmt yuv420p \
-movflags +faststart \
out.mp4 -y