I took over a repository at work. It's a working demo comprising a web server which receives video and camera feeds from a media server (built from the rtsp-simple-server Docker image) via a RTSP relay server and streams the feeds to the client, all deployed via Docker Compose.

I'm trying to switch over to use WebRTC instead. rtsp-simple-server has upgraded into MediaMTX since the time the demo was created 2 years ago. This is the relevant section of the updated Docker Compose configuration:

media-server:
  image: bluenviron/mediamtx:latest-ffmpeg
  expose:
    - 8889
  init: true
  ports:
    - 8889:8889
  restart: unless-stopped
  volumes:
    - type: bind
      source: ./demo/vids
      target: /vids
    - type: bind
      source: ./demo/mediamtx.yml
      target: /mediamtx.yml

Relevant part of the MediaMTX custom configuration in mediamtx.yml:

###############################################
# Path settings
# Settings in "paths" are applied to specific paths, and the map key
# is the name of the path.
# Any setting in "pathDefaults" can be overridden here.
# It's possible to use regular expressions by using a tilde as prefix,
# for example "~test1|test2$" will match both "test1" and "test2",
# for example "~prefix" will match all paths that start with "prefix".
paths:
  \~^(demo\\d $:) runOnDemand: ffmpeg -re -stream\_loop -1 -i /vids/$MTX\_PATH.mp4 -c:v libvpx -b:v 0 -crf 18 -qmin 18 -qmax 18 -f webm http://localhost:8889/$MTX\_PATH/whip

# Settings under path "all_others" are applied to all paths that
# do not match another entry.
all\_others:

I've absolutely no experience with WebRTC. This is my first time hearing of this protocol, let alone working with it. From what I understand, I need to convert my demo mp4 videos (which were successfully streaming via RTSP in the previous implementation) to a compatible video codec, so I've opted for VP8.

Before trying to stream the videos into my web server, I tested the stream directly in the browser (tried with both the latest versions of Chrome and Edge). I went to `http://localhost:8889/demo0` (which should convert demo0.mp4 to VP8 and then stream it over WebRTC). The video player loaded in the browser but no video data was received and nothing played. After several seconds, the screen displayed "Error: bad status code 400, retrying in some seconds". In the browser console, it showed:

Failed to load resource: the server responded with a status of 400 (Bad Request)

Inside the MediaMTX container's runtime logs, this is what's displayed:

2024-04-02 14:53:08 ffmpeg version 6.1.1 Copyright (c) 2000-2023 the FFmpeg developers
2024-04-02 14:53:08   built with gcc 13.2.1 (Alpine 13.2.1\_git20231014) 20231014
2024-04-02 14:53:08   configuration: --prefix=/usr --disable-librtmp --disable-lzma --disable-static --disable-stripping --enable-avfilter --enable-gpl --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libdav1d --enable-libdrm --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-libmp3lame --enable-libopenmpt --enable-libopus --enable-libplacebo --enable-libpulse --enable-librav1e --enable-librist --enable-libsoxr --enable-libsrt --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid --enable-libzimg --enable-libzmq --enable-lto=auto --enable-lv2 --enable-openssl --enable-pic --enable-postproc --enable-pthreads --enable-shared --enable-vaapi --enable-vdpau --enable-version3 --enable-vulkan --optflags=-O3 --enable-libjxl --enable-libsvtav1 --enable-libvpl
2024-04-02 14:53:08   libavutil      58. 29.100 / 58. 29.100
2024-04-02 14:53:08   libavcodec     60. 31.102 / 60. 31.102
2024-04-02 14:53:08   libavformat    60. 16.100 / 60. 16.100
2024-04-02 14:53:08   libavdevice    60.  3.100 / 60.  3.100
2024-04-02 14:53:08   libavfilter     9. 12.100 /  9. 12.100
2024-04-02 14:53:08   libswscale      7.  5.100 /  7.  5.100
2024-04-02 14:53:08   libswresample   5.  0.100 /  5.  0.100
2024-04-02 14:53:08   libpostproc    57.  3.100 / 57.  3.100
2024-04-02 14:53:08 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/vids/demo0.mp4':
2024-04-02 14:53:08   Metadata:
2024-04-02 14:53:08     major\_brand     : isom
2024-04-02 14:53:08     minor\_version   : 512
2024-04-02 14:53:08     compatible\_brands: isomiso2mp41
2024-04-02 14:53:08     encoder         : Lavf58.76.100
2024-04-02 14:53:08   Duration: 00:00:03.47, start: 0.000000, bitrate: 1675 kb/s
2024-04-02 14:53:08   Stream #0:00x1: Video: mpeg1video (mp4v / 0x7634706D), yuv420p(tv, progressive), 640x360 \[SAR 1:1 DAR 16:9\], 104857 kb/s, 30 fps, 30 tbr, 90k tbn (default)
2024-04-02 14:53:08     Metadata:
2024-04-02 14:53:08       handler\_name    : VideoHandler
2024-04-02 14:53:08       vendor\_id       : \[0\]\[0\]\[0\]\[0\]
2024-04-02 14:53:08     Side data:
2024-04-02 14:53:08       cpb: bitrate max/min/avg: 0/0/0 buffer size: 49152 vbv\_delay: N/A
2024-04-02 14:53:08 Stream mapping:
2024-04-02 14:53:08   Stream #0:0 -> #0:0 (mpeg1video (native) -> vp8 (libvpx))
2024-04-02 14:53:08 Press \[q\] to stop, \[?\] for help
2024-04-02 14:53:08 \[libvpx @ 0x7faa8591b8c0\] v1.13.1
2024-04-02 14:53:08 \[libvpx @ 0x7faa8591b8c0\] Bitrate not specified for constrained quality mode, using default of 256kbit/sec
2024-04-02 14:53:08 Output #0, webm, to 'http://localhost:8889/demo0/whip':
2024-04-02 14:53:08   Metadata:
2024-04-02 14:53:08     major\_brand     : isom
2024-04-02 14:53:08     minor\_version   : 512
2024-04-02 14:53:08     compatible\_brands: isomiso2mp41
2024-04-02 14:53:08     encoder         : Lavf60.16.100
2024-04-02 14:53:08   Stream #0:0(und): Video: vp8, yuv420p(tv, progressive), 640x360 \[SAR 1:1 DAR 16:9\], q=2-31, 256 kb/s, 30 fps, 1k tbn (default)
2024-04-02 14:53:08     Metadata:
2024-04-02 14:53:08       handler\_name    : VideoHandler
2024-04-02 14:53:08       vendor\_id       : \[0\]\[0\]\[0\]\[0\]
2024-04-02 14:53:08       encoder         : Lavc60.31.102 libvpx
2024-04-02 14:53:08     Side data:
2024-04-02 14:53:08       cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv\_delay: N/A
2024-04-02 14:53:18 2024/04/02 06:53:18 INF \[path demo0\] runOnDemand command stopped: timed out
2024-04-02 14:53:18 2024/04/02 06:53:18 INF \[WebRTC\] \[session 0f460c76\] closed: source of path 'demo0' has timed out \[out#0/webm @ 0x7faa859487c0\] video:272kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.042856%
2024-04-02 14:53:18 frame=  315 fps= 32 q=18.0 Lsize=     275kB time=00:00:10.46 bitrate= 215.1kbits/s speed=1.05x
2024-04-02 14:53:18 Exiting normally, received signal 2.

I'm not sure what this is supposed to mean? Why isn't the server able to stream this 3-second, 709kb video even once? The browser connected to the server and the URL successfully, but no data was being transferred.

Just in case, I decided to manually convert all of my mp4 files to webm using ffmpeg, and verified with Window's media player that the webm videos work. Then, I modified MediaMTX's configuration to stream the webm videos directly:

paths:
  \~^(demo\\d $:) runOnDemand: ffmpeg -re -stream\_loop -1 -i /vids/$MTX\_PATH.webm -c copy -f webm http://localhost:8889/$MTX\_PATH/whip

However, the error persists:

2024-04-02 15:03:58 ffmpeg version 6.1.1 Copyright (c) 2000-2023 the FFmpeg developers
2024-04-02 15:03:58   built with gcc 13.2.1 (Alpine 13.2.1\_git20231014) 20231014
2024-04-02 15:03:58   configuration: --prefix=/usr --disable-librtmp --disable-lzma --disable-static --disable-stripping --enable-avfilter --enable-gpl --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libdav1d --enable-libdrm --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libharfbuzz --enable-libmp3lame --enable-libopenmpt --enable-libopus --enable-libplacebo --enable-libpulse --enable-librav1e --enable-librist --enable-libsoxr --enable-libsrt --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxml2 --enable-libxvid --enable-libzimg --enable-libzmq --enable-lto=auto --enable-lv2 --enable-openssl --enable-pic --enable-postproc --enable-pthreads --enable-shared --enable-vaapi --enable-vdpau --enable-version3 --enable-vulkan --optflags=-O3 --enable-libjxl --enable-libsvtav1 --enable-libvpl
2024-04-02 15:03:58   libavutil      58. 29.100 / 58. 29.100
2024-04-02 15:03:58   libavcodec     60. 31.102 / 60. 31.102
2024-04-02 15:03:58   libavformat    60. 16.100 / 60. 16.100
2024-04-02 15:03:58   libavdevice    60.  3.100 / 60.  3.100
2024-04-02 15:03:58   libavfilter     9. 12.100 /  9. 12.100
2024-04-02 15:03:58   libswscale      7.  5.100 /  7.  5.100
2024-04-02 15:03:58   libswresample   5.  0.100 /  5.  0.100
2024-04-02 15:03:58   libpostproc    57.  3.100 / 57.  3.100
2024-04-02 15:03:58 Input #0, matroska,webm, from '/vids/demo0.webm':
2024-04-02 15:03:58   Metadata:
2024-04-02 15:03:58     COMPATIBLE\_BRANDS: isomiso2mp41
2024-04-02 15:03:58     MAJOR\_BRAND     : isom
2024-04-02 15:03:58     MINOR\_VERSION   : 512
2024-04-02 15:03:58     ENCODER         : Lavf60.16.100
2024-04-02 15:03:58   Duration: 00:00:03.47, start: 0.000000, bitrate: 217 kb/s
2024-04-02 15:03:58   Stream #0:0: Video: vp8, yuv420p(tv, progressive), 640x360, SAR 1:1 DAR 16:9, 30 fps, 30 tbr, 1k tbn (default)
2024-04-02 15:03:58     Metadata:
2024-04-02 15:03:58       HANDLER\_NAME    : VideoHandler
2024-04-02 15:03:58       VENDOR\_ID       : \[0\]\[0\]\[0\]\[0\]
2024-04-02 15:03:58       ENCODER         : Lavc60.31.102 libvpx
2024-04-02 15:03:58       DURATION        : 00:00:03.466000000
2024-04-02 15:03:58 Output #0, webm, to 'http://localhost:8889/demo0/whip':
2024-04-02 15:03:58   Metadata:
2024-04-02 15:03:58     COMPATIBLE\_BRANDS: isomiso2mp41
2024-04-02 15:03:58     MAJOR\_BRAND     : isom
2024-04-02 15:03:58     MINOR\_VERSION   : 512
2024-04-02 15:03:58     encoder         : Lavf60.16.100
2024-04-02 15:03:58   Stream #0:0: Video: vp8, yuv420p(tv, progressive), 640x360 \[SAR 1:1 DAR 16:9\], q=2-31, 30 fps, 30 tbr, 1k tbn (default)
2024-04-02 15:03:58     Metadata:
2024-04-02 15:03:58       HANDLER\_NAME    : VideoHandler
2024-04-02 15:03:58       VENDOR\_ID       : \[0\]\[0\]\[0\]\[0\]
2024-04-02 15:03:58       ENCODER         : Lavc60.31.102 libvpx
2024-04-02 15:03:58       DURATION        : 00:00:03.466000000
2024-04-02 15:03:58 Stream mapping:
2024-04-02 15:03:58   Stream #0:0 -> #0:0 (copy)
2024-04-02 15:03:58 Press \[q\] to stop, \[?\] for help
2024-04-02 15:04:08 2024/04/02 07:04:08 INF \[path demo0\] runOnDemand command stopped: timed out
2024-04-02 15:04:08 2024/04/02 07:04:08 INF \[WebRTC\] \[session 829664cb\] closed: source of path 'demo0' has timed out \[out#0/webm @ 0x7f04b00515c0\] video:281kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.023511%
2024-04-02 15:04:08 size=     284kB time=00:00:10.49 bitrate= 221.3kbits/s speed=1.05x
2024-04-02 15:04:08 Exiting normally, received signal 2.

This is the same when I try to stream my other videos (demo1.mp4, demo2.mp4 etc.). What am I doing wrong?