Use FFmpeg’s concat demuxer to play compatible prerecorded files in sequence through one encoder output to YouTube Live. The script sets file order and stream-relative timing; it does not schedule blocks for particular clock times or manage YouTube broadcast events. You’ll need to prepare compatible media, create an ffconcat text file, send it to YouTube with your stream URL and key, and manage preview, publication, monitoring, and archiving separately.
What an FFmpeg concat file does—and what it does not do
The concat demuxer reads a text script and processes its listed files one after another. FFmpeg adjusts timestamps so each file starts where the previous one ends. If streams inside the files have different lengths, gaps may occur. The script describes a sequence, not a wall-clock timetable: it does not say “start block two at 9 p.m.” or schedule a YouTube broadcast event.
YouTube treats the broadcast event and the incoming stream as separate resources. The encoder sends media to YouTube using a stream URL and key; Live Control Room preview and the Go live action are part of YouTube’s broadcast workflow. Changing the files in an FFmpeg sequence is not the same as creating or scheduling a YouTube event.
Check whether the files are compatible
Before building the script, inspect every block. FFmpeg’s concat demuxer documentation says: “All files must have the same streams (same codecs, same time base, etc.).” In practice, check that the files have matching stream layouts and compatible codecs and time bases. The demuxer is not a general-purpose converter for arbitrary MP4 files.
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- If the inputs meet the demuxer’s compatibility requirements and you want to avoid re-encoding, the concat demuxer may be suitable.
- If the inputs differ and need to be reconciled through re-encoding, FFmpeg’s FAQ points to the concat filter instead.
- Do not assume that adding
-c copymakes incompatible inputs work. Verify the files and test the resulting transitions before a live broadcast.
Duration metadata matters too. FFmpeg uses a file’s duration to position the next file, so inaccurate duration information can produce timestamp artifacts. If streams within a file do not have matching lengths, the transition may also leave a gap.
Create the ffconcat script
1. Put the blocks in playback order
Create a plain-text file, for example schedule.ffconcat, with one file directive for each block. The first line must be exactly ffconcat version 1.0—with no leading spaces or byte-order mark—if you want FFmpeg to recognize the format automatically.
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ffconcat version 1.0
file 'block-01.mp4'
file 'block-02.mp4'
file 'block-03.mp4'Save the script where FFmpeg can read it, and use paths that resolve from the process’s working directory. Follow FFmpeg’s concat-demuxer escaping rules for spaces and special characters in paths; do not assume ordinary shell quoting alone handles every path in the script.
2. Add duration only when needed
A duration directive can override duration information stored in a file. Use it when the reported duration is missing or inaccurate, and verify the intended cut point against the actual media. The value affects where FFmpeg positions the next file; it is not a clock time at which YouTube will switch content.
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ffconcat version 1.0
file 'block-01.mp4'
duration 600
file 'block-02.mp4'Here, 600 is an example duration in seconds, not a measured length of your file. Do not copy it unless it matches the section you intend to use. The inpoint and outpoint directives can select a portion of a file; confirm the resulting boundaries with a test run, particularly if the files are being concatenated without re-encoding.
Send the sequence to YouTube Live
- Get the ingest details from YouTube Studio. In YouTube Studio’s Live Control Room, set up or select the broadcast and obtain the stream URL and stream key for the encoder workflow. Treat the key as a secret. Never publish it in a command, screenshot, script, or support post.
- Start FFmpeg with the concat input. Point the input at your script and configure the output for the YouTube ingest details and the encoding settings appropriate to your stream. A generic command shape is shown below; replace every placeholder with your own values and options. It is not a complete, universally suitable encoding preset.
- Check the preview. Once FFmpeg is sending media, inspect the Live Control Room preview for picture, sound, and timing issues.
- Publish the event when ready. Use YouTube’s Go live action when appropriate for the broadcast. This is a platform action, separate from the order of files in the concat script.
- Monitor the process and connection. The concat demuxer documents sequential playback, not guaranteed indefinite operation, unattended recovery, or a calendar-based block scheduler. Plan separately for process supervision, network failures, content changes, and recovery.
ffmpeg -f concat -safe 0 -i schedule.ffconcat [input/output options] -f flv 'YOUTUBE_INGEST_URL/YOUR_STREAM_KEY'This is a command template, not a recommendation to copy its placeholders literally. Replace YOUTUBE_INGEST_URL and YOUR_STREAM_KEY with the private ingest details YouTube provides, and supply output options appropriate to your chosen codecs and stream. The example uses -safe 0 to allow paths that may not meet the concat demuxer’s default safe-path rules; use it only when you understand and trust the script’s file paths. Never expose a real stream key.
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Plan block changes, continuous operation, and archives separately
A concat script determines which file follows which, using stream-relative timestamps and duration information. It does not provide a recurring daily timetable, trigger a switch at a specified local time, or itself restart a failed FFmpeg process. Those are operational concerns beyond the sequence file.
Plan replay expectations separately as well. YouTube Help says streams under 12 hours are automatically archived. That statement does not establish that an uninterrupted 24/7 feed will be archived as one video, so do not rely on a single continuous archive outcome for a longer run.
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Troubleshoot common concat-stream problems
- FFmpeg does not recognize the script automatically: Confirm that the very first line is exactly
ffconcat version 1.0, with no extra spaces or byte-order mark. Check that the file is plain text and the path passed to FFmpeg is correct. - A file fails to open: Check the script path, each media path, permissions, and the working directory. Apply FFmpeg’s escaping rules to spaces and special characters. If you use
-safe 0, verify that every referenced path is trusted. - Playback breaks or produces artifacts at a join: Check that the files have the same streams, codecs, and time base. Review duration metadata and any
duration,inpoint, oroutpointdirectives. If the inputs require conversion to match, use the concat filter and re-encode rather than expecting the demuxer to reconcile them. - There is a gap between blocks: Compare the lengths of streams inside the files and verify the duration used for the preceding file. FFmpeg notes that mismatched stream lengths can leave gaps.
- YouTube does not show the expected live picture: Confirm the private stream URL and key, verify FFmpeg is still sending, and inspect the Live Control Room preview. The concat script cannot correct an incorrect ingest configuration or publish the event for you.
- The stream stops and does not resume: The concat demuxer does not promise process supervision or automatic recovery after a process or network failure. Arrange monitoring and a recovery plan outside the script.
- No single archive appears for a long continuous run: YouTube Help’s automatic-archive statement applies to streams under 12 hours; it is not a promise of one archive for an uninterrupted 24/7 stream.
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