Changing container using FFMPEG produces NAL unit error - ffmpeg

Question

Background:
My current videofile is put in a Linux based system that streams content (RTP) to other users. I'm filming and sending the content to the server after I change the and make sure the encoding is correct I stumble upon issues.
I've tried doing this using ffmpeg, however the system I'm injecting this file in won't recognize it and stream it to another device.
I'm doing all the transcoding and such on a Windows system
C:\Users\mazdak\Documents\Projects\ffmpeg\bin>ffmpeg -y -i input.mp4 -pix_fmt yuv420p -c:v libx264 -profile:v main -level:v 4.1 -color_range 0 -colorspace bt709 -x264opts colorprim=bt709:transfer=bt709:bframes=1 -an output.mkv
Error:
What I'm getting is
StreamMedia exception ry: Unexpected NAL unit type: 9
(...)
StreamMedia exception ry: First media frame must be sync point
Maybe I'm not preparing it for RTSP? Is that the issue. Cause what I see is that the files that are able to stream are encoded using Gstreamer
So I thought.. perhaps ffmpeg does not do that? well let's give gst-launch a try.
I need pointers as to how to go about this.
What I have:
OSSBuild of GStreamer
ffmpeg utils
input.mp4 - H264 Main profile L3.1 - Pixel format yuvj420p
Audio in container
What I need (probably):
output.mkv- H264 Main profile L4.1 - Pixel format yuv420p - RTP prepared (rtph264pay module)
Audio removed
I have h264_analyze output from both the movie I filmed. From the movie that is successfully streamed, and the movies from my attempts with ffmpeg

Answer 1

So this question can go in a whole bunch of different directions depending on what you're trying to do. Here is a very basic pipeline that just re-muxes h264 video data in an mp4 file into an mkv file. It ignores the audio. No re-encoding is necessary.
gst-launch-0.10 filesrc location="bbb.mp4" ! qtdemux ! video/x-h264 !
h264parse ! matroskamux ! filesink location=/tmp/bbb.mkv
Here is another pipeline that demuxes an mp4 file, re-encodes it using the out-of-the-box x264 settings, and re-muxes it into an mkv file.
gst-launch-0.10 filesrc location="bbb.mp4" ! decodebin2 !
videoconvert ! x264enc ! h264parse ! matroskamux ! filesink
location=/tmp/bbb2.mkv
Video formats are usually more like a bundle of data than an individual file. A the top level you have your container formats (mp4, mkv, etc.), then often within those containers you have video and audio data stored in various formats (h264 video, AAC audio, etc.). Then at the streaming level you have protocols like RTP (RTSP is a sort of wrapper protocol for negotiating one or more RTP streams) and MPEGTS.
You may also want to double check what your camera is producing. You can run ffprobe on it:
ffprobe whatever.mp4
You can also try creating simple test videos from scratch to see if GStreamer can even make anything your server can understand.
gst-launch-0.10 videotestsrc num-buffers=120 ! ffmpegcolorspace ! x264enc profile=main ! h264parse ! matroskamux ! filesink location=/tmp/main.mkv
gst-launch-0.10 videotestsrc num-buffers=120 ! ffmpegcolorspace ! x264enc profile=baseline ! h264parse ! matroskamux ! filesink location=/tmp/baseline.mkv
gst-launch-0.10 videotestsrc num-buffers=120 ! ffmpegcolorspace ! x264enc profile=high ! h264parse ! matroskamux ! filesink location=/tmp/high.mkv

Answer 2

My guess is that input.mp4 contains NAL of type 9 (as the error message points out).
"Access unit delimiters" (NAL type 9) should not be in an mp4.
To me it looks like your camera is muxing an illegal h.264 bitstream format into input.mp4.
MP4s should contain size prefixed NALs and no SPS (type 7), PPS (type 8) or AUs (type 9).
Now the question is how to filter out the AUs or just pass them through.
I would try a stream copy - dropping the audio - see: https://ffmpeg.org/ffmpeg.html#Stream-copy