[mp4 @ 0x7fe98400dc00] track 1: could not find tag, codec not currently supported in container This means that pcm_mulaw is not allowed in the MP4 output container format. Your choices are: Use a different output container format ffmpeg -i input -codec copy output.mkv Or re-encode the audio ffmpeg -i input -c:v copy -c:a aac output.mp4

IP cameras are of varying quality, some behaving erratically in my experience. Dealing with their RTSP streams requires a dose of fault-tolerance.