[Cin] Dynamic_input filters and avfilter_pad_get_type

9 May 2025

      I was looking at why our application (cinelerra-gg) crashed at trying to
use libplacebo

I found that libplacebo defines itself

https://ffmpeg.org/doxygen/7.0/vf__libplacebo_8c.html

as

 .flags = AVFILTER_FLAG_HWDEVICE
<https://ffmpeg.org/doxygen/7.0/group__lavfi.html#ga01e3b7175b4477235061256f3398eecc>
| AVFILTER_FLAG_DYNAMIC_INPUTS
<https://ffmpeg.org/doxygen/7.0/group__lavfi.html#gae6ed6c10a03508829bdf17560e3e10e5>
,

so only output pad is defined, as far as I can see:

static const AVFilterPad
<https://ffmpeg.org/doxygen/7.0/structAVFilterPad.html> libplacebo_outputs
<https://ffmpeg.org/doxygen/7.0/vf__libplacebo_8c.html#a3545e8f08cc238430300b27efc10cdaf>[]
= {
  {
  .name
<https://ffmpeg.org/doxygen/7.0/structAVFilterPad.html#afc112061a6035639934e0135aab7d425>
= "default",
  .type = AVMEDIA_TYPE_VIDEO
<https://ffmpeg.org/doxygen/7.0/group__lavu__misc.html#gga9a84bba4713dfced21a1a56163be1f48ac1a46f59be5c6c2d3412ab172d6b8cf5>
,
  .config_props = &libplacebo_config_output
<https://ffmpeg.org/doxygen/7.0/vf__libplacebo_8c.html#a09a97380118a876bb5fce38315c70f6a>
,
  },
 };

then when our code calls

avfilter_pad_get_type()

it promptly crashes.

 BC_Signals::dump_stack
cin() [0x8b2c9e2]
linux-gate.so.1(__kernel_rt_sigreturn+0) [0xf7fb8590]
cin(avfilter_pad_get_type+0x14) [0x99266a4]
cin(_ZN13FFVideoStream13create_filterEPKc+0xbc) [0x865669c]
cin(_ZN6FFMPEG12open_decoderEv+0x80f) [0x865732f]
cin(_ZN10FileFFMPEG9check_sigEP5Asset+0x81) [0x8670071]
cin(_ZN4File5probeEv+0x376) [0x867cd86]
cin(_ZN4File9open_fileEP11PreferencesP5Assetii+0x378) [0x867d628]
cin(_ZN7MWindow14load_filenamesEP9ArrayListIPcEiii+0x250) [0x87301f0]
cin(_ZN17CommandLineThread3runEv+0x53) [0x86e2cd3]
cin(_ZN6Thread10entrypointEPv+0x41) [0x8b70c11]
/lib/libpthread.so.0(+0x7328) [0xf7df9328]
/lib/libc.so.6(clone+0x66) [0xf0373f06]

We still hope to get libplacebo's tonemapping  + vulkan hevc decoding
going, so any pointers how to talk to those dynamic_input filters will be
useful. Even swscale is dynamic_input in ffmpeg 7.1+, so I (we) really hope
to keep it working, too.

Code:

https://git.cinelerra-gg.org/git/?p=goodguy/cinelerra.git;a=blob;f=cinelerra...

[Cin] Dynamic_input filters and avfilter_pad_get_type

Andrew Randrianasulu