[FFmpeg-trac] #9830(ffmpeg:reopened): Reuse of linklabel as input pad silently uses first unused input stream (was: Overlaying an image to multiple streams doesn't work as expected (only the first call of the overlay gets the overlay))

[FFmpeg]

#9830: Reuse of linklabel as input pad silently uses first unused input stream
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             Reporter:  janezkuhar  |                    Owner:  (none)
                 Type:  defect      |                   Status:  reopened
             Priority:  normal      |                Component:  ffmpeg
              Version:              |               Resolution:
             Keywords:              |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
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Changes (by Gyan):

 * status:  closed => reopened
 * resolution:  invalid =>
 * summary:
     Overlaying an image to multiple streams doesn't work as expected (only
     the first call of the overlay gets the overlay)
     =>
     Reuse of linklabel as input pad silently uses first unused input
     stream

Comment:

 The OP doesn't specify the bug clearly.

 Here's an example command:

 {{{
 ffmpeg -i hd720.mp4 -i hd1080.mp4 -filter_complex
 "[1]hue=s=0[v];[v][v]concat" out.mp4
 }}}

 Only a single stream with label `v` is generated from hd1080.mp4. It is
 referenced twice as input in the concat filter. The concat filter should
 either repeat the hue-processed stream twice or error out. Instead, it
 tries to concat hd720.mp4 as the 2nd stream. But the user did not type
 `[0]` or leave the 2nd input pad blank.

 `avfilter_graph_parse2` should fail this graph.
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Ticket URL: <https://trac.ffmpeg.org/ticket/9830#comment:3>
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