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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchKeep one FFmpeg output running and join the prerecorded videos into a continuous program. Use the concat demuxer when the files are compatible for packet-level joining; use the concat filter when you need to normalize or re-encode them. Neither method guarantees a clean cut for every source or what viewers see on YouTube, so inspect transitions in your actual output.
Choose the right concat method
| Method | What it does | Best fit | Main caveat |
|---|---|---|---|
| Concat demuxer | Reads a manifest and joins inputs at the packet level, avoiding re-encoding when compatible. | Sources with matching stream properties and a suitable container/output workflow. | Compatibility matters; inaccurate duration information can cause artifacts, and edit points do not guarantee a clean visual cut. FFmpeg concat demuxer documentation |
| Concat filter | Decodes and joins streams in a filtergraph, then encodes the result. | Sources that need normalization or re-encoding. FFmpeg’s FAQ recommends this approach when re-encoding is needed. | Requires deliberate handling of stream layout and output encoding. FFmpeg FAQ |
| Concat protocol | Concatenates resources at the protocol level. | Only workflows for which its specific constraints are met. | It is not interchangeable with the demuxer or filter; check the format and protocol requirements in the FFmpeg documentation. |
For a fixed playlist, build one continuous output rather than stopping and restarting FFmpeg for every video. Restarting the encoder can interrupt the outgoing stream; joining files inside one process avoids that particular handoff, but does not by itself prove there will be no black frame.
Inspect and prepare the videos
Before choosing a command, compare every source. Use ffprobe to inspect codecs, dimensions, frame rates, pixel formats, time bases, audio presence, sample rates, channel layouts, and durations. The aim is to identify differences that could make packet-level joining unsuitable or require normalization.
- Check that every file has the video and audio streams you intend to include.
- Compare dimensions, frame rate, codec parameters, pixel format, and time base.
- Compare audio sample rate and channel layout; a missing audio stream in one clip needs an explicit plan.
- Confirm durations and intended cut points rather than relying on guessed values.
- Check the installed FFmpeg version and its local help: the online documentation tracks the newest revision and can differ from an older local build. FFmpeg documentation
Option 1: use a concat-demuxer manifest
Try the demuxer when the clips are compatible for packet-level joining and your output workflow supports it. Create a plain-text manifest such as playlist.txt:
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file 'video-a.mp4'
file 'video-b.mp4'
file 'video-c.mp4'Then read the manifest as the input to FFmpeg. For example, to produce a file for inspection without re-encoding:
ffmpeg -f concat -safe 0 -i playlist.txt -map 0:v:0 -map 0:a:0? -c copy joined.mp4This example assumes the files are accessible at the listed paths, have compatible streams, and can be copied into the chosen output container. The optional audio map allows an input with no audio stream, but it does not create audio for a silent clip. If clips have different stream layouts, do not assume this command will reconcile them.
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The demuxer accepts directives including durations and edit points. Do not add estimated durations just to force a transition: FFmpeg warns that inaccurate duration information can cause artifacts. With non-intra-frame codecs, packets or decoded frames around an inpoint or outpoint can also fall outside the apparent cut. A manifest edit point is not a guarantee of a clean visual boundary. See the concat demuxer documentation.
Option 2: normalize with the concat filter
Use the concat filter when the inputs differ or packet-level joining causes boundary problems. Each input must be decoded, brought to a consistent format, joined, and encoded as one output. The following pattern assumes both clips have video and stereo audio; adapt the normalization and mapping to the files you inspected:
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ffmpeg -i video-a.mp4 -i video-b.mp4
-filter_complex "[0:v]scale=1920:1080,fps=30,format=yuv420p,setpts=PTS-STARTPTS[v0];[1:v]scale=1920:1080,fps=30,format=yuv420p,setpts=PTS-STARTPTS[v1];[0:a]aresample=48000,aformat=channel_layouts=stereo,asetpts=PTS-STARTPTS[a0];[1:a]aresample=48000,aformat=channel_layouts=stereo,asetpts=PTS-STARTPTS[a1];[v0][a0][v1][a1]concat=n=2:v=1:a=1[v][a]"
-map "[v]" -map "[a]" -c:v libx264 -pix_fmt yuv420p -c:a aac joined.mp4This is a template, not a universal command. Replace the scale, frame rate, pixel format, audio layout, codecs, and output settings to suit the intended program and encoder. It expects an audio stream in each input. If one clip is silent or has a different channel layout, provide a suitable audio stream or adjust the filtergraph; do not leave the filter inputs mismatched.
Filtergraph outputs need explicit mapping. A labeled output such as [v] or [a] must be mapped once and exactly once. More generally, explicit -map options prevent FFmpeg’s automatic stream-selection rules from choosing a different video or audio stream than intended. FFmpeg stream selection and mapping.
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Send the continuous output to YouTube Live
Once you have a joined file, or a filtergraph that emits the full sequence, connect that continuous FFmpeg output to the YouTube Live ingest using the stream key and output protocol/settings appropriate to your local FFmpeg build and YouTube’s current setup. The concat examples above create a file for inspection; they do not specify a universal YouTube publishing command. In particular, do not assume a file-joining example alone establishes the required ingest URL, encoder settings, or YouTube-side behavior.
Keep the output process alive across the sequence. Check the stream key carefully, keep it private, and use the intended video and audio maps rather than relying on automatic selection. For a fixed sequence, the playlist must be built into the continuous program; the cited FFmpeg documentation does not establish a particular runtime controller for interactive source switching.
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Validate transitions before relying on the stream
Record or inspect the produced output around every boundary, including both picture and sound. Check the last frames of one clip and the first frames of the next, and listen for a gap, abrupt level change, or missing audio. Repeat for every transition: a successful join at one boundary does not establish that all source pairs behave the same.
If the output looks clean locally but viewers still report a black frame, the available FFmpeg concat documentation cannot identify the cause. Encoder timestamps, GOP structure, audio continuity, stream protocol, platform processing, and playback state are possibilities to investigate—not verified causes for a particular stream. Do not treat a local test as a guarantee of YouTube playback.
Troubleshooting common boundary problems
- Concat demuxer reports errors or the output fails: verify manifest paths and syntax, then compare the source stream parameters. If the files are not compatible for packet-level joining, normalize and use the concat filter.
- A visual glitch appears at a cut: inspect inpoint/outpoint behavior and duration values. Non-intra-frame codecs can include packets or decoded frames around edit boundaries; do not assume a manifest edit point trims every boundary cleanly.
- Audio drops out or changes unexpectedly: inspect whether each source has audio and compare sample rate and channel layout. Adjust the filtergraph or provide a deliberate silent track where needed; map the intended audio output explicitly.
- The wrong video or audio appears: add explicit input or filter-output mappings. FFmpeg’s automatic selection can choose streams based on properties such as resolution or channel count rather than your intended playlist track.
- The local joined file is clean but the live playback is not: separate the file-joining test from the ingest and playback path. Check the actual outgoing stream and YouTube playback without claiming the concat method guarantees platform behavior.
- Documentation examples do not match your FFmpeg build: check the installed version and local option help. The online manual reflects a continually developing project and may describe a newer revision.
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