How to convert OBS MKV recordings to MP4 ready for WhatsApp with FFmpeg

To convert the latest OBS video recording into a format fully compatible with WhatsApp, use the following ffmpeg command:

ffmpeg -i "$(ls -t ~/obs/*.mkv | head -n 1)" \
  -c:v libx264 -pix_fmt yuv420p -profile:v main -level 4.0 \
  -c:a aac -b:a 128k \
  -movflags +faststart \
  whatsapp_ready.mp4

Explanation of flags and why they are needed

• -i "$(ls -t ~/obs/*.mkv | head -n 1)" Finds .mkv files in ~/obs, sorts them by modification time (ls -t), and picks the newest one (head -n 1). Automatically passes the latest recording as input to ffmpeg.
• -c:v libx264 Sets the video codec to H.264 (AVC). This is the most universally accepted video codec by WhatsApp and hardware decoders on mobile devices.
• -pix_fmt yuv420p Forces the pixel format to YUV 4:2:0 (8-bit). OBS or GPU encoders often record in 4:4:4 or 10-bit color (e.g. yuv420p10le), which results in a black screen or playback error on WhatsApp.
• -profile:v main -level 4.0 Restricts the H.264 profile to Main and level to 4.0. Prevents using high profiles (like High 5.2) that may be rejected by mobile WhatsApp apps.
• -c:a aac -b:a 128k Encodes audio to AAC at 128 kbps bitrate. Default audio tracks in OBS MKV files (such as Opus or raw PCM) are not played back in WhatsApp MP4 videos.
• -movflags +faststart Moves the file header metadata (the moov atom) to the beginning of the file. This allows the video to start playing immediately while downloading or uploading in the chat window.
• whatsapp_ready.mp4 Output file name in MP4 container format. MKV files from OBS are not natively supported by the WhatsApp media player.