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Short answer: you generally cannot add a video to a running FFmpeg concat playlist just by appending a line to its text file. FFmpeg’s documentation describes how the concat demuxer reads a prepared list, but does not promise that an active process monitors or reloads edits. For videos known in advance, prepare the list before starting FFmpeg. For videos that arrive mid-stream, use a queue or controller designed to hand off the next input while the FFmpeg output session remains active—and test that implementation with your installed FFmpeg version and YouTube setup.
Why editing the playlist file may not work
The 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, so do not assume that adding a new file line will make an active stream play it. That is a limit of what the documented behavior guarantees, not a claim that every build or custom setup behaves identically. See the FFmpeg concat demuxer documentation.
FFmpeg’s general model is to read inputs supplied with -i and write an output to a destination URL; it supports RTMP as a protocol. That input/output model does not itself provide a live queue that watches a concat script. See FFmpeg’s command-line documentation and RTMP protocol documentation.
Choose the right workflow
| Question | Prepared concat list | Live queue or controller |
|---|---|---|
| When are the videos available? | Before FFmpeg starts | Additional videos may arrive during the session |
| What happens if you edit the list after startup? | Do not assume FFmpeg reloads it | The queue/controller selects and hands off subsequent inputs |
| File requirements | Inputs should have matching streams, codecs, and time bases | The controller must also handle differences or normalize/transcode inputs |
| Complexity | Lower | Higher; handoffs and failures need implementation and testing |
| Output | 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 documented FFmpeg feature or a tested, universal command. The transition behavior depends on the controller and handoff method you choose.
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When all videos are known before streaming
Use the concat demuxer with a text file containing one file directive per video, then pass that list to FFmpeg as an input. This is the straightforward case: construct the complete sequence before the process starts. The concat demuxer’s intended use requires compatible input streams, codecs, and time bases. If the files differ, stream-copy concatenation may not reconcile them; a normalization or transcoding workflow may be needed.
- Prepare the list. Create a text file with a
fileline for each source video, in the order you want them played. Use paths that the FFmpeg process can access. - Check compatibility. Confirm that the listed inputs have matching stream layouts, codecs, and time bases for the concat demuxer. If they do not, determine a suitable normalization or transcoding path before going live.
- Start FFmpeg with the list as an input. Use the concat demuxer input and write to your configured streaming URL. FFmpeg accepts inputs through
-iand sends the output to the URL you specify; the exact command depends on your media, output settings, and destination configuration. Consult the concat documentation and the documentation for your installed FFmpeg version.
Accurate durations matter when using concat scripts: inaccurate duration information can produce timestamp gaps or artifacts. Check the concat documentation for the format and constraints rather than assuming that any list of files will join cleanly.
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When a video arrives after the stream has started
Appending a line to the concat script is not a documented live-queue mechanism. Instead, use an external playlist manager or controller that can select the next video and hand it to FFmpeg when the current input finishes, while FFmpeg continues writing to the same output endpoint. The queue needs to manage the transition between inputs; it is not enough merely to change a text file that the running process may not reread.
- Define the handoff. Decide how the controller detects that the current video has ended and supplies the next input without ending the outgoing session.
- Handle incompatible files. If incoming videos have different stream layouts, codecs, or time bases, the controller or media pipeline must account for those differences, potentially by normalizing or transcoding.
- Test before relying on it. Try the exact queue, handoff method, installed FFmpeg build, and destination you intend to use. Check whether the transition creates a pause or other visible or audible discontinuity; do not describe it as seamless until your specific setup demonstrates that.
- Plan for failures. Decide what the controller should do if a file is missing, unreadable, incompatible, or not ready when the current video ends. The implementation must define this behavior; FFmpeg’s concat documentation does not provide a universal queue policy.
There is no one-size-fits-all command here: the required wrapper or controller, file compatibility, and tolerance for transition gaps affect the implementation. The relevant documented distinction is that FFmpeg reads inputs and writes an output, while live selection and handoff must be provided by the system around it.
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Do not confuse an HLS segment playlist with an input queue
FFmpeg’s HLS muxer produces media segments and an HLS playlist. Its append_list option concerns carrying forward entries in that output segment playlist and removing #EXT-X-ENDLIST. It does not document adding a new local source video to a running FFmpeg input list for a YouTube RTMP stream. If your destination is YouTube ingest rather than HLS delivery, HLS playlist options do not solve the input-queue problem. See the FFmpeg HLS muxer documentation.
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Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Version and destination checks
FFmpeg’s online documentation is regenerated as the project evolves. Match syntax and option behavior to the version installed on the machine running the stream. This guide does not establish YouTube-specific bitrate limits, reconnect rules, protocol requirements, or session-duration guarantees; check YouTube’s current live-streaming guidance for those settings before configuring an ingest session.
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