[ISSUE] ffmpeg RTMP server functionality broken when built with `--enable-librtmp`

[ISSUE] ffmpeg RTMP server functionality broken when built with `--enable-librtmp`

[TinfoilSubmarine]

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New issue by TinfoilSubmarine on void-packages repository

https://github.com/void-linux/void-packages/issues/52353

Description:
### Is this a new report?

Yes

### System Info

Void 6.6.52_1 x86_64 AuthenticAMD uptodate rrmFFFFFFFFFFFFFFFFFFFFFFFF

### Package(s) Affected

ffmpeg6-6.1.2_2

### Does a report exist for this bug with the project's home (upstream) and/or another distro?

_No response_

### Expected behaviour

Running `ffmpeg -listen 1 -i rtmp://192.168.1.235:1935/test -f h264 - | ffplay -` should listen for an incoming stream, then display a video.

### Actual behaviour

```
$ ffmpeg -listen 1 -i rtmp://192.168.1.235:1935/test -f h264 - | ffplay -                                                                                                                                                    
ffmpeg version 6.1.2ffplay version 6.1.2 Copyright (c) 2003-2024 the FFmpeg developers
  built with gcc 13.2.0 (GCC)
 Copyright (c) 2000-2024 the FFmpeg developers
  built with gcc 13.2.0 (GCC)
  configuration: --prefix=/usr --disable-debug --enable-gpl --enable-gnutls --disable-stripping --enable-libcdio --enable-version3 --enable-runtime-cpudetect --enable-libmp3lame --enable-libvorbis --enable-libxvid --enable-libx264 --enable-libvpx --enable-libtheora --enable-shared --enable-static --enable-libxcb --enable-libpulse --enable-libfreetype --enable-libmodplug --enable-libspeex --enable-libcelt --enable-libass --enable-libopus --enable-librtmp --enable-libjack --disable-libopencore_amrnb --disable-libopencore_amrwb --disable-libopenjpeg --enable-libbluray --enable-postproc --enable-opencl --enable-libvmaf --enable-libx265 --enable-libv4l2 --enable-libaom --enable-libbs2b --enable-libvidstab --enable-libdav1d --enable-libsrt --enable-librist --enable-libwebp --enable-vulkan --enable-libdrm --enable-libsvtav1 --enable-vaapi --enable-vdpau --disable-libzimg --disable-libmysofa --enable-libvpl --enable-nvenc --enable-nvdec
  configuration: --prefix=/usr --disable-debug --enable-gpl --enable-gnutls --disable-stripping --enable-libcdio --enable-version3 --enable-runtime-cpudetect --enable-libmp3lame --enable-libvorbis --enable-libxvid --enable-libx264 --enable-libvpx --enable-libtheora --enable-shared --enable-static --enable-libxcb --enable-libpulse --enable-libfreetype --enable-libmodplug --enable-libspeex --enable-libcelt --enable-libass --enable-libopus --enable-librtmp --enable-libjack --disable-libopencore_amrnb --disable-libopencore_amrwb --disable-libopenjpeg --enable-libbluray --enable-postproc --enable-opencl --enable-libvmaf --enable-libx265 --enable-libv4l2 --enable-libaom --enable-libbs2b --enable-libvidstab --enable-libdav1d --enable-libsrt --enable-librist --enable-libwebp --enable-vulkan --enable-libdrm --enable-libsvtav1 --enable-vaapi --enable-vdpau --disable-libzimg --disable-libmysofa --enable-libvpl --enable-nvenc --enable-nvdec
  libavutil      58. 29.100 / 58. 29.100
  libavcodec     60. 31.102 / 60. 31.102
  libavformat    60. 16.100 / 60. 16.100
  libavdevice    60.  3.100 / 60.  3.100
  libavfilter     9. 12.100 /  9. 12.100
  libswscale      7.  5.100 /  7.  5.100
  libswresample   4. 12.100 /  4. 12.100
  libpostproc    57.  3.100 / 57.  3.100
  libavutil      58. 29.100 / 58. 29.100
  libavcodec     60. 31.102 / 60. 31.102
  libavformat    60. 16.100 / 60. 16.100
  libavdevice    60.  3.100 / 60.  3.100
  libavfilter     9. 12.100 /  9. 12.100
  libswscale      7.  5.100 /  7.  5.100
  libswresample   4. 12.100 /  4. 12.100
  libpostproc    57.  3.100 / 57.  3.100
RTMP_Connect0, failed to connect socket. 111 (Connection refused)
[in#0 @ 0x55c4d2f5eb40] Error opening input: Unknown error occurred
Error opening input file rtmp://192.168.1.235:1935/test.
Error opening input files: Unknown error occurred
fd:: Invalid data found when processing input 0KB sq=    0B f=0/0
```

### Steps to reproduce

1. Have ffmpeg listen for an RTMP stream: `ffmpeg -listen 1 -i rtmp://192.168.1.235:1935/test -f h264 - | ffplay -`
2. Stream something to the RTMP url.
3. See error above.

Re: ffmpeg RTMP server functionality broken when built with `--enable-librtmp`

[TinfoilSubmarine]

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New comment by TinfoilSubmarine on void-packages repository

https://github.com/void-linux/void-packages/issues/52353#issuecomment-2375114497

Comment:
I have tested with a build of ffmpeg omitting `--enable-librtmp` and can confirm this error does not occur.

Re: ffmpeg RTMP server functionality broken when built with `--enable-librtmp`

[tm512]

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New comment by tm512 on void-packages repository

https://github.com/void-linux/void-packages/issues/52353#issuecomment-2403638296

Comment:
At least in the past, librtmp builds also had connectivity issues while streaming (would randomly disconnect), prompting me to make my personal builds with it disabled. At this point I'm not sure if librtmp offers any useful features that ffmpeg's native RTMP doesn't yet have.