Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsA black gap between playlist videos does not identify a single cause. Start by checking how FFmpeg joins the files: the concat demuxer places each file according to duration information, and FFmpeg warns that timestamp adjustment can create gaps when streams in a file do not have exactly the same length. Incorrect duration metadata or mismatched streams can also disrupt transitions. Inspect the files and FFmpeg output before changing the command, then check YouTube’s stream health to see whether the issue is already present at ingestion.
Why a black gap can appear between playlist videos
With FFmpeg’s concat demuxer, timestamps are adjusted so the first file starts at zero and each next file starts where the previous one finishes, using file duration information. The FFmpeg project warns that this adjustment is global and may cause gaps if the streams do not have exactly the same length. Duration metadata can also be inaccurate—for example, when duration is estimated from bitrate or a file is truncated—and FFmpeg notes that this can cause artifacts. FFmpeg’s concat demuxer documentation describes both behaviors.
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A black picture may instead be present in a source clip or arise later in encoding, YouTube ingestion, or playback. Without the playlist, media probes, command, logs, and stream-health details, it is not possible to tell which stage introduced it. Treat the gap as a symptom to trace, not proof that one particular FFmpeg option is wrong.
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1. Probe every playlist file
Run ffprobe on each file in the playlist and compare the results. Check the number and types of streams, codecs, time bases, reported duration, frame rate, dimensions, and audio properties. The concat demuxer’s documented compatibility requirement is that the files have the same streams, codecs, and time bases. Differences in the other properties are useful clues that the clips may need a common output format or further inspection.
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Compare the reported durations with the actual playback near each file’s end. Look for truncated files, an unexpected black tail, or an audio or video stream that ends noticeably earlier than its partner. Do not assume that a duration shown by a probe is correct merely because it is present.
2. Check playlist order and duration assumptions
Confirm that the concat file lists the intended paths in the intended order. For each entry, compare the duration FFmpeg is using with the clip’s observed end. If the metadata is demonstrably wrong, the concat demuxer supports a per-file duration directive to override the stored duration. Use an override only after establishing the correct duration; an inaccurate correction can shift the next file just as an inaccurate source value can.
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3. Choose stream copy or re-encoding based on the probes
Stream copy copies encoded packets without decoding, filtering, or encoding. It can avoid re-encoding when the input streams are compatible and their timing is sound, but it does not normalize incompatible streams or repair incorrect duration metadata. FFmpeg’s documentation on stream copy explains what it does; the FFmpeg FAQ describes the concat demuxer as useful when avoiding re-encoding and the media format does not support file-level concatenation. Neither is a guarantee that arbitrary clips can be joined with -c copy.
- Use stream copy as a candidate when the files meet the concat compatibility requirements and the duration and timestamp checks do not show a problem.
- Correct duration metadata when inspection shows that duration information is the cause and you can establish an accurate value.
- Consider decoding, filtering, and re-encoding when the clips are incompatible or need normalization for continuous output. The required audio and video handling depends on the files, so there is no safe universal filter command for an unspecified playlist.
4. Inspect FFmpeg output at the transition
Keep the exact command and logs from a reproduction. Examine the period around the gap for timestamp discontinuities, duration warnings, dropped or duplicated frames, and differences between the clips’ audio and video streams. If possible, inspect the output file or outgoing stream at the same transition. This helps distinguish a gap already in a source from one introduced during concatenation or later in the delivery chain.
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5. Check YouTube’s stream health and encoder settings
Use YouTube’s stream-health information as a separate diagnostic layer rather than assuming every visible gap originates in the playlist. The YouTube LiveStreams resource exposes stream-health status for diagnosing streaming problems. If the issue appears at ingestion, review the encoder configuration as well as the media timing.
YouTube Help’s general live encoder guidance recommends CBR and a two-second keyframe interval, and says not to exceed four seconds. These are encoder recommendations, not proof that keyframe timing caused a particular playlist gap; supported settings also depend on resolution, frame rate, and protocol. Check the current YouTube encoder settings guidance for the configuration you use. For HLS ingestion, consult YouTube’s separate HLS delivery guidance.
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Common symptoms and the next check
| What you observe | What to check next |
|---|---|
| The gap happens at the same playlist boundary each time. | Inspect both adjacent clips’ stream lengths and duration metadata, then review FFmpeg logs around that boundary. |
| The gap shifts or varies between runs. | Compare the files’ reported durations with observed playback and look for timestamp or duration warnings in the logs. |
| Only some clips cause a gap. | Compare their stream count, codecs, time bases, frame rate, dimensions, and audio properties with clips that join cleanly. |
| The concatenated output looks continuous locally, but the YouTube stream does not. | Check YouTube stream health and the encoder settings; the issue may occur after local concatenation. |
| A gap remains after changing to stream copy. | Recheck compatibility and timing. Stream copy does not correct bad duration metadata or normalize incompatible streams. |
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