Short answer: You should not assume FFmpeg will notice a new line appended to a concat playlist while a stream is running. The concat demuxer reads a script of files, but its documentation does not promise live reloading. If videos may arrive after the stream starts, use a queue or controller to supply the next input while keeping FFmpeg’s output session alive—and test the handoff with your installed FFmpeg version and destination.
Why editing a running concat playlist is not enough
FFmpeg’s concat demuxer reads a script of files and treats their packets as if they had been muxed together in sequence. Its documentation does not state that a running process watches the script for changes or reloads it when you append a line. The reliable assumption is therefore that editing the file alone will not add a video to a stream already in progress. FFmpeg concat demuxer documentation
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FFmpeg accepts inputs with -i and writes to an output URL; RTMP is supported through FFmpeg’s protocol handling. Those input/output building blocks do not, by themselves, turn a concat script into a live queue. FFmpeg documentation FFmpeg RTMP protocol documentation
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| Question | Concat list prepared before streaming | Queue or controller during a live session |
|---|---|---|
| When are the videos known? | Before FFmpeg starts | New videos may arrive after streaming begins |
| What happens if you edit a list after startup? | Do not assume FFmpeg reloads it | The controller manages which input comes next |
| Compatibility work | Inputs should have matching streams, codecs, and time bases | The controller must still handle differences or normalize/transcode inputs |
| Complexity | Lower | Higher: implement and test handoffs and failure handling |
| Output session | FFmpeg writes the prepared sequence to the configured output URL | Keep the output process/session active while changing the supplied input |
The live-queue approach is an architectural pattern, not a concat-demuxer feature specification or a tested universal implementation. Which handoff method works depends on your controller, the input files, and your FFmpeg build.
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If all videos are known before you go live
Prepare a concat script before launching FFmpeg. Use one file directive per source file; for example:
file '/path/to/video-1.mp4'
file '/path/to/video-2.mp4'
file '/path/to/video-3.mp4'Save it as a text file, such as playlist.txt. Then pass the script as the concat input and direct FFmpeg’s output to your configured streaming URL. A schematic command is:
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ffmpeg -f concat -safe 0 -i playlist.txt -c copy -f flv "YOUR_CONFIGURED_STREAM_URL"This is a template, not a verified YouTube ingest command. Replace the output URL with the one configured for your destination, and check the installed FFmpeg documentation for the version-specific options. The -c copy path is appropriate only when the inputs are compatible for concatenation; it does not reconcile mismatched codecs, stream layouts, or time bases. Incorrect duration information can also lead to timestamp gaps or artifacts. If files differ, consider normalizing or transcoding them rather than expecting stream copy to make them seamless. FFmpeg concat demuxer documentation
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Use an external playlist manager or queue/controller to select and hand off each subsequent video while the FFmpeg output session remains active. The queue needs to manage the transition from one input to the next; FFmpeg must continue writing to the same output endpoint. Appending to the concat script is not a documented substitute for that controller.
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Plan and test the handoff
- Check your constraints. Determine whether you can run a wrapper or controller that launches or controls FFmpeg, whether the incoming files share compatible codecs and stream layouts, and whether a brief gap between videos is acceptable.
- Choose how inputs will be handed off. Select a queue/controller implementation that can provide the next file when the current one ends without replacing the active output session. The concat documentation does not specify a universal live-input queue or a guaranteed seamless handoff.
- Test with your actual setup. Use the FFmpeg version installed on the streaming machine, representative files, and your intended destination. Verify transitions and recovery behavior before relying on it for a live channel; do not describe a method as seamless until your own tests establish that.
- Handle incompatible files deliberately. If incoming videos differ in stream layout, codecs, or time bases, make normalization or transcoding part of the workflow where needed. A controller does not remove input-compatibility requirements.
FFmpeg’s online documentation is regenerated as the project evolves, so check the documentation corresponding to your installed build. The available documentation does not establish current YouTube-specific bitrate limits, reconnect rules, protocol requirements, or session-duration guarantees; consult YouTube’s current Live guidance for those details rather than inferring them from FFmpeg’s concat behavior.
Do not confuse HLS playlist options with an RTMP input queue
If by “playlist” you mean an HLS output playlist, FFmpeg’s HLS muxer has a separate append_list option. It carries forward an existing HLS segment list and removes #EXT-X-ENDLIST. That applies to the playlist of generated HLS segments; it does not append a new local source video to an input list for a YouTube RTMP stream. FFmpeg HLS muxer documentation
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Troubleshooting playlist updates and handoffs
- A new file never plays after you append it: A running concat demuxer is not documented to watch or reload its script. Prepare the list before startup, or use a queue/controller for videos that arrive during the session.
- The stream reaches the end of the prepared list: The prebuilt concat workflow contains only the inputs listed before FFmpeg starts. For later arrivals, design a controller to supply the next input while preserving the output session.
- There are timestamp gaps or playback artifacts: Check whether the concat inputs have matching streams, codecs, and time bases, and whether duration information is accurate. Normalize or transcode files that do not meet the needed compatibility conditions.
- A supposed live update works on one machine but not another: Do not treat that behavior as a documented guarantee. Verify the method against the installed FFmpeg version and the exact handoff implementation.
- You enabled HLS
append_listbut new source videos do not enter the stream: That option concerns an HLS output segment playlist, not a live RTMP input queue.
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