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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →When an FFmpeg playlist glitches at a clip change or logs “non-monotonous DTS,” start by checking the files, stream compatibility, and duration metadata—not by adding a timestamp flag. The concat demuxer already shifts timestamps between files, but it relies on compatible streams and accurate durations. Use the diagnostic steps below to find the boundary that fails, test a local join, and only then check YouTube Live ingest settings.
What causes timestamp problems in a looping playlist?
With the concat demuxer, FFmpeg reads packets from each listed file in sequence. It shifts timestamps so the first file starts at zero and later files start when the preceding file is estimated to end. That means a source file’s timestamps resetting to zero do not automatically explain a failure.
The estimate depends on each file’s duration. If duration metadata is wrong—for example, because it was inferred from bitrate or the file is truncated—the next file may start at an unsuitable time. Unequal audio and video stream lengths can also leave gaps. In addition, concat stream copy assumes the files have the same streams, codecs, and time base; differences can produce artifacts or errors at clip boundaries.
A “non-monotonous DTS” log message is a symptom, not a diagnosis. The right fix depends on the actual files, FFmpeg build, packet timestamps, and the point in the playlist where the first bad timestamp appears.
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Diagnose the failing boundary before changing timestamps
- Save the complete log. Note the first error and whether it happens at a transition between two clips or only when playback returns from the last clip to the first.
- Check the playlist. Confirm the file order and paths refer to the intended media. Pay particular attention to the last-to-first transition if the problem occurs only after a full pass.
- Compare the inputs. For each file, inspect stream count, codecs, time bases, frame rates, audio formats, and reported duration. Compare the two files on either side of the first failing boundary, as well as the last and first files in a loop.
- Check file integrity and duration. Look for truncated or damaged files and duration values that do not match the actual media. If the correct duration is independently known, the concat script supports a per-file
durationdirective; do not guess a replacement value. - Test the joined media locally. Resolve file and stream issues, then play through every transition and the loop boundary before adding YouTube as another variable.
FFmpeg’s concat demuxer documentation describes its stream compatibility assumptions and duration behavior, including the possibility of artifacts when durations are inaccurate.
Build a compatible playlist
Use stream copy only when the inputs match
Stream copy avoids re-encoding, but it does not make different inputs equivalent. Use it only when the files meet the concat demuxer’s same-stream, codec, and time-base requirements, and their durations are reliable. If one clip has a different stream layout or encoding parameters, first create normalized intermediate files or transcode the set to consistent properties.
Use re-encoding as a normalization fallback
If the sources cannot be made suitable for stream copy, re-encoding is a practical diagnostic fallback: it can normalize dissimilar sources into a consistent output. It requires enough CPU for continuous encoding and may reduce image quality if the encoding settings are poorly chosen. Check audio/video sync and playback across transitions after normalizing.
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Choose between copying and encoding based on whether the streams and time bases match, whether durations are accurate, the compute available for continuous encoding, the desired quality, and sync at transitions. A clean local join is a prerequisite for isolating a YouTube ingest problem; it does not establish that the live ingest configuration is correct.
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Loop and pace the input for live output
A typical input is an ffconcat text file with one file directive per clip. Pass it to FFmpeg with -f concat -i playlist.ffconcat. For a file-based live process, -stream_loop -1 repeats the input indefinitely, while -re reads it at its native rate rather than sending it as fast as possible. These options control repetition and pacing; neither fixes mismatched streams or inaccurate durations.
Input-scoped options belong before the input they apply to. For example, the input portion of a command can be arranged as ffmpeg -re -stream_loop -1 -f concat -i playlist.ffconcat. Add the output and encoder options appropriate to your chosen YouTube ingest settings only after the local sequence is sound. See the FFmpeg command-line documentation for the current semantics of -stream_loop and -re.
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This is an input setup, not a universal complete streaming command: output options depend on whether you are copying or encoding and on your stream’s codec, resolution, frame rate, and audio. Keep your YouTube stream key secret.
Change timestamps only when the evidence points there
Timestamp tools are not interchangeable fixes. FFmpeg’s setts bitstream filter can assign expressions to PTS, DTS, duration, or time base, but its documentation explains the mechanics rather than promising a recipe for every playlist. In particular, setting PTS equal to DTS is labeled not recommended when B-frames are involved.
Avoid adding -copyts, -copytb, -fflags +genpts, or -avoid_negative_ts as generic remedies. Their effects depend on the demuxer, codecs, time base, and whether the stream is copied or encoded. Use one only when inspection of the affected stream gives you a specific reason, then verify synchronization and playback through the boundary again. Consult the FFmpeg setts documentation and the help for your installed build before changing behavior.
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Do not copy the historical -force_dts_monotonicity option from a 2018 development-list patch into a current command as though it were a supported modern fix. That post described a proposed patch and cautioned that interactions with other flags had not been fully analyzed. The March 16, 2018 FFmpeg development-list post is historical discussion, not proof that the option is available in your release.
Check YouTube Live settings separately
Once the joined output is clean locally, check encoder configuration and stream health in YouTube Live. YouTube’s current encoder settings guidance lists RTMP/RTMPS; H.264, H.265 (HEVC), or AV1 video; AAC or MP3 audio; constant bitrate (CBR); and frame rates up to 60 fps. It recommends a two-second keyframe interval and says not to exceed four seconds. Its bitrate recommendations vary by resolution, codec, and frame rate, so choose from the current table for your actual output rather than applying one generic bitrate.
YouTube recommends RTMPS. In the encoder setup, use the YouTube server URL and stream key; the YouTube encoder setup instructions explain where to enter them. Treat the key like a password.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsLocal timestamp correctness and YouTube ingest compatibility are separate checks: a clean local concat does not guarantee successful ingest, and valid ingest settings do not repair a bad local timestamp sequence. Test before going live, monitor stream health, and use the specific messages in Live Control Room to investigate the ingest branch.
Troubleshoot by symptom
| Symptom | Likely area to inspect | Next step |
|---|---|---|
| Glitch or timestamp error at a particular clip change | Stream layout, codecs, time bases, or duration for the two adjacent files | Compare both inputs and normalize or transcode if they do not meet concat compatibility assumptions. |
| Problem only when the playlist returns to its first clip | Last-to-first boundary, including the last file’s duration and stream compatibility with the first | Inspect that boundary as carefully as any other transition; test the full sequence locally. |
| Gap between audio and video or a pause at a transition | Unequal audio/video lengths or inaccurate duration metadata | Verify the actual durations and file integrity; use an explicit concat duration only when the correct value is known. |
| Joined file plays correctly, but YouTube reports an unhealthy or failed stream | Encoder output settings or YouTube ingest | Check the selected codec, audio format, CBR, keyframe interval, resolution-specific bitrate, server URL, and stream health messages. |
| A timestamp flag changes the error but causes sync problems | Flag behavior interacting with the demuxer, codec, time base, or copied/encoded output | Undo generic changes and return to the diagnosed boundary; apply timestamp rewriting only for an identified stream issue and retest sync. |
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