FFmpeg’s concat demuxer plays files in the order you list them; it does not shuffle or prevent adjacent repeats. Generate an episode order that avoids choosing the episode played immediately before, write that order to an ffconcat script, then pass the script to FFmpeg. For compatible files, the concat demuxer can join them without re-encoding.
Build an episode order with no adjacent repeats
First decide which episodes are eligible for this playlist. The shuffle rule belongs in the playlist-generation step, not in FFmpeg: while choosing the next episode, exclude the one selected immediately before it whenever another eligible choice exists.
- Collect the episode files for this run.
- Choose an order while enforcing
next_episode != previous_episode. If every episode is used exactly once, you can shuffle and check the resulting order, reshuffling if two adjacent entries match. A constrained selector can instead choose from the remaining episodes other than the previous one whenever possible. - Write the selected paths to a text file in ffconcat format.
If episodes have different repeat counts, the constraint may not be achievable. A valid no-adjacent-repeat ordering requires the most frequent episode’s remaining count to be no greater than the combined count of all alternatives plus one.
Write the ffconcat playlist
Use this structure, replacing the sample paths with your chosen episode files:
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ffconcat version 1.0
file '/media/Bluey/S01E01.mp4'
file '/media/Bluey/S01E03.mp4'
file '/media/Puffin Rock/S01E02.mp4'The first line must be exactly ffconcat version 1.0 and must appear first for automatic format recognition. Paths with spaces or special characters need quoting or escaping according to the concat script syntax. Consult the FFmpeg concat demuxer documentation if a path is not being parsed as intended.
Concatenate compatible files without re-encoding
When the files have compatible streams and properties, run:
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ffmpeg -f concat -safe 0 -i playlist.ffconcat -map 0 -c copy shuffled.mp4This uses stream copy rather than re-encoding. The concat demuxer expects the inputs to have the same streams and compatible properties, such as codecs and time bases. Incorrect duration information can cause timestamp gaps or other artifacts. If durations need to be specified, the script syntax supports duration directives; otherwise, normalize the inputs before concatenating. Check the result at episode boundaries, especially when sources differ.
When to use the concat filter instead
If the files are not suitable for stream-copy concatenation, or you need to re-encode them into a consistent output, use FFmpeg’s concat filter workflow instead. The filter joins decoded streams and allows re-encoding; the demuxer is the appropriate route when the inputs are compatible and avoiding re-encoding is the goal. The FFmpeg FAQ on concatenating video files describes the distinction.
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A shuffled file is not an indefinitely changing playlist
The command above creates one finite output in the order already generated. When it ends, it cannot provide fresh randomness or remember the last episode for the next run. For recurring playback, the system that generates or serves the next playlist must apply the same adjacency rule across playlist boundaries—for example, by excluding the final episode of the previous list from the next list’s first choice. The precise integration depends on the player and whether it accepts dynamic playlists.
Troubleshoot common problems
- The files play in the original order: FFmpeg follows the order in the script. Check that your playlist generator wrote the shuffled order to the file you passed with
-i. - The script is not recognized: Confirm that
ffconcat version 1.0is the exact first line, with no blank line or other text before it. - A path with spaces or punctuation fails: Quote or escape the path using concat script syntax, then test that entry in the playlist.
- Stream copy fails or the output has glitches: The inputs may differ in streams or properties, or may contain inaccurate duration information. Use the concat filter with re-encoding when the inputs need normalization; verify episode transitions in the output.
- The next playlist starts with the same episode that just ended: Apply the no-repeat check across the boundary too. The generator needs to know the last episode from the previous playlist.
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