ffmpeg：如何将 vstack 与 _filter_complex 中的其他选项链接起来

Question

I am using an RTSP input stream and divide it in two identical. On the first one I just do a scaling, on the second one I do a scaling and a close up as well. So both streams [a] and [b] have the same dimensions aferwards:

-filter_complex "[0:v]split=2[in1][in2];[in1]scale=800:600[a];[in2]crop=640:360:700:500,scale=800:600[b]" \

No I am trying to create a stream from [a] and [b] called [c] to stack both together:

-filter_complex "[0:v]split=2[in1][in2];[in1]scale=800:600[a];[in2]crop=640:360:700:500,scale=800:600[b];[a][b]vstack=inputs=2[c]" \

While the first one works, I get the following error message for the second one:

Output with label 'a' does not exist in any defined filter graph, or was already used elsewhere.

How can I chain the operations to that I can map a third stream an process it with

-map "[a]"
-map "[b]"
-map "[c]"

Answer 1

@kesh: Thanks!

I modified it like this and it works:

-filter_complex "[0:v]split=2[in1][in2];[in1]scale=800:600[a];\ 
 [in2]crop=640:360:700:500,scale=800:600[b];\
 [a]split=2[a1][a2];[b]split=2[b1][b2];[a1][b1]vstack=inputs=2[c]" \

-map "[a2]" ...
-map "[b2]" ...
-map "[c]" ...