unix+rtp with ffmpeg does not work

[kalle-crystalspace]

Question

I am unable to get rtp+unix working as described here

mediamtx.yml file:

  mypath:
    source: unix+rtp:///tmp/socket.sock
    rtpSDP: |
      v=0
      o=- 123456789 123456789 IN IP4 192.168.1.100
      s=H264 Video Stream
      c=IN IP4 192.168.1.100
      t=0 0
      m=video 5004 RTP/AVP 96
      a=rtpmap:96 H264/90000
      a=fmtp:96 profile-level-id=42e01e;packetization-mode=1;sprop-parameter-sets=Z0LAHtkDxWhAAAADAEAAAAwDxYuS,aMuMsg==

ffmpeg command:

 ffmpeg -hide_banner -re -f lavfi -i testsrc=size=1280x720:rate=30 -c:v libx264 -pix_fmt yuv420p -preset ultrafast -b:v 600k -f rtp unix:/tmp/socket.sock

mediamtx output:

$ ./mediamtx 
2025/09/26 10:09:40 INF MediaMTX v1.15.1
2025/09/26 10:09:40 INF configuration loaded from /home/kalle/sandbox/mediamtx/mediamtx.yml
2025/09/26 10:09:40 INF [path mypath] [RTP source] started
2025/09/26 10:09:40 INF [RTSP] listener opened on :8554 (TCP), :8000 (UDP/RTP), :8001 (UDP/RTCP)
2025/09/26 10:09:40 INF [RTMP] listener opened on :1935
2025/09/26 10:09:40 INF [HLS] listener opened on :8888
2025/09/26 10:09:41 INF [WebRTC] listener opened on :8889 (HTTP), :8189 (ICE/UDP)
2025/09/26 10:09:41 INF [SRT] listener opened on :8890 (UDP)
2025/09/26 10:09:43 ERR [path mypath] [RTP source] EOF

ffmpeg output:

$ ffmpeg -hide_banner -loglevel debug -re -f lavfi -i testsrc=size=1280x720:rate=30 -c:v libx264 -pix_fmt yuv420p -preset ultrafast -b:v 600k -f rtp unix:/tmp/socket.sock
Splitting the commandline.
Reading option '-hide_banner' ... matched as option 'hide_banner' (do not show program banner) with argument '1'.
Reading option '-loglevel' ... matched as option 'loglevel' (set logging level) with argument 'debug'.
Reading option '-re' ... matched as option 're' (read input at native frame rate; equivalent to -readrate 1) with argument '1'.
Reading option '-f' ... matched as option 'f' (force format) with argument 'lavfi'.
Reading option '-i' ... matched as output url with argument 'testsrc=size=1280x720:rate=30'.
Reading option '-c:v' ... matched as option 'c' (codec name) with argument 'libx264'.
Reading option '-pix_fmt' ... matched as option 'pix_fmt' (set pixel format) with argument 'yuv420p'.
Reading option '-preset' ... matched as AVOption 'preset' with argument 'ultrafast'.
Reading option '-b:v' ... matched as option 'b' (video bitrate (please use -b:v)) with argument '600k'.
Reading option '-f' ... matched as option 'f' (force format) with argument 'rtp'.
Reading option 'unix:/tmp/socket.sock' ... matched as output url.
Finished splitting the commandline.
Parsing a group of options: global .
Applying option hide_banner (do not show program banner) with argument 1.
Applying option loglevel (set logging level) with argument debug.
Successfully parsed a group of options.
Parsing a group of options: input url testsrc=size=1280x720:rate=30.
Applying option re (read input at native frame rate; equivalent to -readrate 1) with argument 1.
Applying option f (force format) with argument lavfi.
Successfully parsed a group of options.
Opening an input file: testsrc=size=1280x720:rate=30.
[AVFilterGraph @ 0x587e083c25c0] Setting 'size' to value '1280x720'
[AVFilterGraph @ 0x587e083c25c0] Setting 'rate' to value '30'
detected 8 logical cores
[Parsed_testsrc_0 @ 0x587e083c4280] size:1280x720 rate:30/1 duration:-1.000000 sar:1/1
[AVFilterGraph @ 0x587e083c25c0] query_formats: 2 queried, 1 merged, 0 already done, 0 delayed
[lavfi @ 0x587e083c2080] All info found
Input #0, lavfi, from 'testsrc=size=1280x720:rate=30':
  Duration: N/A, start: 0.000000, bitrate: N/A
  Stream #0:0, 1, 1/30: Video: wrapped_avframe, 1 reference frame, rgb24, 1280x720 [SAR 1:1 DAR 16:9], 0/1, 30 fps, 30 tbr, 30 tbn
Successfully opened the file.
Parsing a group of options: output url unix:/tmp/socket.sock.
Applying option c:v (codec name) with argument libx264.
Applying option pix_fmt (set pixel format) with argument yuv420p.
Applying option b:v (video bitrate (please use -b:v)) with argument 600k.
Applying option f (force format) with argument rtp.
Successfully parsed a group of options.
Opening an output file: unix:/tmp/socket.sock.
[out#0/rtp @ 0x587e083c6b00] No explicit maps, mapping streams automatically...
[vost#0:0/libx264 @ 0x587e083c7e00] Created video stream from input stream 0:0
[unix @ 0x587e083ca940] No default whitelist set
Successfully opened the file.
Stream mapping:
  Stream #0:0 -> #0:0 (wrapped_avframe (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[graph 0 input from stream 0:0 @ 0x587e083d4bc0] Setting 'video_size' to value '1280x720'
[graph 0 input from stream 0:0 @ 0x587e083d4bc0] Setting 'pix_fmt' to value '2'
[graph 0 input from stream 0:0 @ 0x587e083d4bc0] Setting 'time_base' to value '1/30'
[graph 0 input from stream 0:0 @ 0x587e083d4bc0] Setting 'pixel_aspect' to value '1/1'
[graph 0 input from stream 0:0 @ 0x587e083d4bc0] Setting 'frame_rate' to value '30/1'
[graph 0 input from stream 0:0 @ 0x587e083d4bc0] w:1280 h:720 pixfmt:rgb24 tb:1/30 fr:30/1 sar:1/1
[format @ 0x587e083d5240] Setting 'pix_fmts' to value 'yuv420p'
[auto_scale_0 @ 0x587e083d5f00] w:iw h:ih flags:'' interl:0
[format @ 0x587e083d5240] auto-inserting filter 'auto_scale_0' between the filter 'Parsed_null_0' and the filter 'format'
[AVFilterGraph @ 0x587e083c6900] query_formats: 4 queried, 2 merged, 1 already done, 0 delayed
[auto_scale_0 @ 0x587e083d5f00] w:1280 h:720 fmt:rgb24 sar:1/1 -> w:1280 h:720 fmt:yuv420p sar:1/1 flags:0x00000004
[libx264 @ 0x587e083c8200] using mv_range_thread = 24
[libx264 @ 0x587e083c8200] using SAR=1/1
[libx264 @ 0x587e083c8200] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0x587e083c8200] profile Constrained Baseline, level 3.1, 4:2:0, 8-bit
[rtp @ 0x587e083c76c0] Max packet size 0 too low
[out#0/rtp @ 0x587e083c6b00] Could not write header (incorrect codec parameters ?): Input/output error
Error while filtering: Input/output error
[vist#0:0/wrapped_avframe @ 0x587e083c6dc0] Decoder thread received EOF packet
[vist#0:0/wrapped_avframe @ 0x587e083c6dc0] Decoder returned EOF, finishing
[vist#0:0/wrapped_avframe @ 0x587e083c6dc0] Terminating decoder thread
[out#0/rtp @ 0x587e083c6b00] Nothing was written into output file, because at least one of its streams received no packets.
frame=    0 fps=0.0 q=0.0 Lsize=       0kB time=N/A bitrate=N/A speed=N/A    
[libx264 @ 0x587e083c8200] final ratefactor: 36.69
[AVIOContext @ 0x587e083d2ac0] Statistics: 0 bytes written, 0 seeks, 0 writeouts
[in#0/lavfi @ 0x587e083c1f80] Terminating demuxer thread
[in#0/lavfi @ 0x587e083c1f80] Input file #0 (testsrc=size=1280x720:rate=30):
[in#0/lavfi @ 0x587e083c1f80]   Input stream #0:0 (video): 3 packets read (1440 bytes); 1 frames decoded; 0 decode errors; 
[in#0/lavfi @ 0x587e083c1f80]   Total: 3 packets (1440 bytes) demuxed
Conversion failed!