Appending a new line to an FFmpeg concat playlist is not a documented way to add a video to a stream that is already running. If the videos are known before you go live, prepare a concat list first. If new videos may arrive during the stream, use a queue or controller that hands FFmpeg the next input while keeping its output session alive—and test that handoff with your installed FFmpeg version.
Why editing a running concat list is not enough
The concat demuxer reads a script of files and treats their packets as if they had been muxed together in sequence. FFmpeg’s documentation does not promise that a running process watches that script for changes or reloads appended lines. Do not assume a playlist edit will make the current stream play the new file.
That distinction matters: the concat list is an input description, while the outgoing stream is an output written to a URL. Keeping the output alive while changing which input comes next requires a mechanism to manage the input handoff; editing the original script alone is not a documented live queue.
If every video is known before streaming starts
Use the concat demuxer for a prebuilt sequence. Create a text file with one file directive per video, then pass that file to FFmpeg as the input and write to your configured streaming URL. For example, the list can be structured like this:
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file '/path/to/video-01.mp4'
file '/path/to/video-02.mp4'
file '/path/to/video-03.mp4'Use paths that are valid from the directory and environment where FFmpeg runs. Check the concat demuxer documentation for the installed version if paths need special handling.
The files should have matching stream layouts, codecs, and time bases for the demuxer’s intended use. Stream-copy concatenation should not be expected to reconcile videos with different properties. If the files differ, you may need to normalize or transcode them through a suitable workflow. Inaccurate duration information can also cause timestamp gaps or artifacts.
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If videos arrive after the stream has started
Use an external playlist manager or queue/controller to select and hand off each next video while the FFmpeg output session remains active. The controller needs to coordinate the transition between inputs, and FFmpeg must continue writing to the same configured output endpoint.
This is an architecture pattern based on FFmpeg’s input/output model, not a built-in live-reload guarantee or a tested, universal command. The exact handoff depends on your FFmpeg build and how the controller supplies inputs. Test it before relying on it for a continuous stream.
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Plan the handoff before going live
- Decide whether the controller can launch or control FFmpeg and supply each next input.
- Check whether all videos have compatible codecs and stream layouts. If not, decide how to normalize or transcode them.
- Decide whether a brief gap between videos is acceptable. Do not call the result seamless until you have tested the actual transition.
- Test the queue, input transition, and continued output with the FFmpeg version installed on the streaming machine and the destination you intend to use.
Prebuilt list or live queue?
| Decision | Prebuilt concat list | Live queue/controller |
|---|---|---|
| When to use it | All videos are known before FFmpeg starts. | Videos may arrive during the session. |
| What happens to edits after startup | Do not assume the running process reloads them. | The controller handles subsequent selections and handoffs. |
| File compatibility | Matching streams, codecs, and time bases are expected for the demuxer’s intended use. | The controller still needs to handle differences or normalize/transcode inputs. |
| Operational work | Lower: prepare the list before starting. | Higher: implement and test handoff and failure handling. |
| Output session | FFmpeg writes the sequence to the configured output URL. | Keep the output process/session alive while changing the supplied input. |
Do not confuse HLS append_list with an RTMP input queue
FFmpeg’s HLS muxer creates a playlist of media segments. Its append_list option carries forward an existing HLS segment list and removes #EXT-X-ENDLIST. That concerns an HLS output playlist; it does not append a new local source video to the input list for a YouTube RTMP stream.
Check the FFmpeg version and destination behavior
FFmpeg’s online documentation evolves with the project, so check the documentation matching the version installed on your streaming machine. FFmpeg accepts inputs with -i and writes output to an output URL; RTMP is handled through its protocol support. The exact queue handoff and YouTube-specific ingest requirements are not established here, so verify them for your own build and destination rather than assuming a particular bitrate, reconnect behavior, or session guarantee.
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