Merge one audio file and one image file to create a video with ffmpeg

Problems with your command #2:

• Frame rate is too low. Most players are unable to play 1 fps. Use 10 fps or higher for output, or set input -framerate to 10 fps or higher.
• Chroma subsampling. Most players can only play 4:2:0, so use the format filter to force it to 4:2:0.
• MP3 in MP4. Some players are unable to play MP3 in MP4. For highest compatibility use AAC. ffmpeg will choose AAC by default for MP4.
• Faststart (optional). Add -movflags +faststart so MP4 can begin playback faster.

Command:

ffmpeg -framerate 1 -loop 1 -i image.jpg -i audio.mp3 -vf format=yuv420p -r 10 -shortest -movflags +faststart output.mp4