Reuse of linklabel as input pad silently uses first unused input stream

[janezkuhar]

Summary of the bug:
How to reproduce:

% ffmpeg -i INPUT.mp4 -i test_logo.png -filter_complex "overlay=x=(main_w-overlay_w)/2:y=(main_h-overlay_h)/2,split=outputs=6[v0][v1][v2][v3][v4][v5]; [v0][v1][v2]hstack=inputs=3[top]; [v3][v4][v5]hstack=inputs=3[bottom]; [top][bottom]vstack=inputs=2" OUTPUT.mp4

ffmpeg version 4.3.4-0+deb11u1 Copyright (c) 2000-2021 the FFmpeg developers
built with gcc 10 (Debian 10.2.1-6)

[janezkuhar]

​https://superuser.com/questions/1731191/add-logo-to-multiple-input-videos-in-ffmpeg

[Elon Musk]

Use split filters, any other way is not supported.

[Gyan]

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 or error out. Instead, it tries to concat hd720.mp4 as the 2nd stream. But the user did not type [0], or omit the 2nd input pad.

avfilter_graph_parse2 should fail this graph.

[janezkuhar]

Replying to Elon Musk:

Use split filters, any other way is not supported.

Thank you for this, and apologies for the meaningless report.