How to Transcode Video to RealVideo Using FFmpeg

This guide provides a quick overview and step-by-step instructions on how to transcode modern video files into the legacy RealVideo format using FFmpeg. You will learn the exact command-line syntax, the necessary video and audio codecs to use, and how to configure the output container for maximum compatibility with legacy RealPlayer media players.

To transcode a video to the RealVideo format, you need to use the RealVideo encoder (typically rv10 or rv20) and the RealAudio encoder (real_144) packaged inside a RealMedia (.rm) container.

Run the following command in your terminal to perform the conversion:

ffmpeg -i input.mp4 -c:v rv20 -c:a real_144 -b:v 500k output.rm

Command Breakdown

• -i input.mp4: Specifies the path to your source video file.
• -c:v rv20: Sets the video codec to RealVideo 2.0 (G2). You can also use rv10 for RealVideo 1.0, though rv20 offers slightly better compression.
• -c:a real_144: Sets the audio codec to RealAudio 1.0 (14.4k). This is the standard audio codec used for classic RealMedia files.
• -b:v 500k: Sets the video bitrate to 500 kbps. You can adjust this value higher or lower depending on your desired file size and quality.
• output.rm: The output file name. The .rm extension tells FFmpeg to mux the streams into a RealMedia container.

Important Compatibility Notes

Because RealVideo and RealAudio are legacy formats, FFmpeg has strict limitations when encoding them:

1. Audio Bitrate: The real_144 audio encoder only supports a constant bitrate of 8000 bps (8 kbps) and requires a sample rate of 8000 Hz. FFmpeg will automatically resample the audio to meet these requirements during transcoding.
2. Resolution Constraints: Legacy RealVideo codecs work best with standard-definition resolutions (such as 320x240 or 640x480). If your source video is 1080p or 4K, scale it down using the video filter flag -vf scale=640:-1 to avoid encoding errors and playback lag.