Why Reddit Videos Download Without Sound — And How to Fix It with FFmpeg

Description and use

Downloaded Reddit videos often lack sound because audio and video are served separately. Using FFmpeg or yt-dlp to merge the streams restores audio.

Problem

Downloaded Reddit videos often lack audio because Reddit delivers video and audio as separate streams.

Outcome

Combining separate Reddit video and audio streams with FFmpeg (or yt-dlp) restores sound to silent downloads.

Workflow

• Identify separate video and audio URLs from Reddit’s media endpoints.
• Download the video-only MP4 and audio-only M4A files.
• Use ffmpeg to merge streams: ffmpeg -i video_only.mp4 -i audio_only.m4a -map 0:v:0 -map 1:a:0 -c copy -movflags +faststart output.mp4.
• If audio codec incompatible, re‑encode audio: ffmpeg -i video_only.mp4 -i audio_only.m4a -map 0:v:0 -map 1:a:0 -c:v copy -c:a aac -b:a 128k output.mp4.
• Verify merged file with ffprobe to ensure both video and audio streams are present.
• Optionally use yt-dlp with -f "bv+ba/b" and --merge-output-format mp4 to automate download and merge.

Evidence

Reddit often delivers video and audio as separate streams.

Source

ffmpeg -i video_only.mp4 -i audio_only.m4a -map 0:v:0 -map 1:a:0 -c copy -movflags +faststart output.mp4

Source

yt-dlp -f "bv+ba/b" --merge-output-format mp4 "https://www.reddit.com/..."

Source