Use FFmpeg’s concat demuxer to play a fixed list of compatible files in sequence without restarting the command. Put the filenames in a text list, then pass that list to FFmpeg with -f concat. For a live network stream, this handles the media sequence only: you must also configure an output format, transport, and destination supported by the receiving service.
Choose the right FFmpeg concat method
FFmpeg has three concat mechanisms, and they solve different problems. The concat demuxer is usually the simplest choice when your files have matching streams and you want to avoid re-encoding. Use the concat filter when inputs need normalization or otherwise differ. The concat protocol treats supported resources as one resource at the file level; it is not a general-purpose joiner for arbitrary containers. See the FFmpeg FAQ for the distinctions.
| Need | Method | Main constraint |
|---|---|---|
| Sequence similarly encoded files without re-encoding | Concat demuxer | Inputs need matching streams, codecs, and time bases; duration metadata affects timestamps. |
| Combine files that differ or need normalization | Concat filter, followed by encoding | Choose compatible output codecs and encoding settings. |
| Join resources in a format that supports file-level concatenation | Concat protocol | Only certain formats support it; shell escaping may be needed. |
Build a concat-demuxer list
Create a plain-text file named list.ffconcat beside your videos:
ffconcat version 1.0
file 'first.mp4'
file 'second.mp4'
file 'third.mp4'The header must be the exact first line, without a byte-order mark or extra spaces, for automatic recognition. Add one file directive per input; their order is playback order. Quote or escape paths containing spaces or special characters. The concat demuxer documentation describes the script syntax and path safety rules.
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For ordinary relative filenames, leave off -safe 0. The demuxer restricts paths by default; use -safe 0 only when the list deliberately uses trusted paths outside that safe subset, such as absolute paths.
Join compatible files without re-encoding
For files whose streams are compatible, run:
ffmpeg -f concat -i list.ffconcat -c copy output.mp4-c copy copies encoded packets; it does not decode, filter, or re-encode them. This is fast and avoids generation loss, but it cannot make mismatched streams compatible. The concat demuxer requires the files to have the same streams, including matching codecs and time bases; check stream layout and parameters such as dimensions, frame rate, and audio before relying on stream copy. Consult the FFmpeg command-line manual for option behavior and ordering.
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Handle mismatched inputs
If files have different stream layouts or encoding parameters, normalize them to a common format or use the concat filter and encode a new output. The filter operates on decoded media, so you need to select output video and audio codecs and encoding settings appropriate for your use. The FFmpeg FAQ recommends the filter when re-encoding is required. A stream-copy command is not a substitute for that normalization.
Publish the sequence to a live destination
To send the sequence to a network destination, keep the concat list as the input and replace output.mp4 with the output format, protocol, and destination required by the receiving service. The output options must match that service’s current ingest instructions, including its supported transport and codecs. There is no universal publish command because the destination is not specified here; obtain the ingest URL, stream key, and required settings from the service you intend to use.
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Concatenation selects and timestamps the media sequence. It does not by itself configure a live stream, guarantee reconnection, or make a finite list endless. A fixed list is played in order; files added later are not automatically included by virtue of editing the list. For a playlist that must continue indefinitely or adapt to new files, you need a separate scheduling or process-management design. The FFmpeg concat references do not establish a general hot-reload guarantee for list edits.
Check timestamps and continuity
The demuxer starts the first file at timestamp zero and offsets each later file using the preceding file’s duration. If a file is truncated or its stored duration is inaccurate, the next file can start at an incorrect timestamp, causing gaps or artifacts. The demuxer documentation describes the timestamp behavior and allows a duration directive in the list to override an inaccurate or missing duration.
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- Verify every intended filename is present and in the right order.
- Check that stream-copy inputs have the same streams, codecs, and time bases.
- If a transition has a gap or timestamp artifact, inspect the preceding file’s duration and consider an explicit duration directive.
- For changing playlists, use a design that explicitly manages updates rather than assuming a static list will reload.
When the concat protocol fits
The concat protocol reads supported resources in sequence as a single resource, using syntax like concat:URL1|URL2|.... It is intended for formats that support this kind of file-level concatenation, such as MPEG program stream, not arbitrary MP4 joins. For example, the FFmpeg protocols documentation shows ffplay concat:split1.mpeg|split2.mpeg|split3.mpeg; the vertical bars are escaped for the shell. The FAQ also gives an MPEG example using -i concat:"intermediate1.mpg|intermediate2.mpg" and stream-copying to a combined MPEG output: FFmpeg FAQ.
Troubleshoot common failures
- FFmpeg does not recognize the list automatically: Make
ffconcat version 1.0the exact first line, with no byte-order mark or leading text. - A filename is rejected: Check quoting and escaping. If the path is outside the safe relative-path subset, use
-safe 0only for a trusted local list. - Stream copy fails or playback breaks at a join: Compare streams, codecs, time bases, dimensions, frame rates, and audio layout. Normalize differing files or use the concat filter and encode.
- A gap or artifact appears at a transition: Inspect duration metadata for the preceding input; an inaccurate duration can misplace the next file’s timestamps.
- The live stream does not reach its destination: The concat input is separate from publishing. Verify the destination’s current ingest URL, stream key, output format, transport, codecs, and required output options.
- New files do not appear in the sequence: A static list describes the files supplied to that run; it does not establish automatic list reloading. Use an explicit playlist manager or scheduling process for dynamic additions.
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