There is no universal FFmpeg flag that fixes timestamp errors in every looping playlist. First find out whether the problem begins at a clip boundary or when the playlist returns to its first clip, then check the concat list, stream compatibility, and clip durations. Only change timestamps after you have identified a specific timestamp issue; options such as -stream_loop -1 and -re control looping and pacing, not timestamp repair.
Why timestamps can break at a playlist boundary
FFmpeg’s concat demuxer reads files in sequence and adjusts their timestamps so the first file starts at zero and each later file starts when the previous one is estimated to end. That depends on the files being compatible: the concat demuxer expects the same streams, codecs, and time bases in each file. It uses each file’s duration to position the next one, so inaccurate duration metadata can cause gaps or artifacts. Unequal audio and video lengths can also create gaps.
A “non-monotonous DTS” message is a symptom, not a diagnosis. Timestamp resets inside source files are not automatically the cause: concat already adjusts timestamps between files. Identify where the first bad timestamp appears, and investigate that boundary before changing packet timestamps.
Diagnose the failing boundary first
- Save the complete FFmpeg log. Note whether the first error appears when moving to a particular clip, or only when the sequence returns to its first clip.
- Verify the playlist. Check the order and every file path against the files you intend to stream.
- Compare the clips. Inspect stream count, codecs, time bases, frame rates, audio formats, and reported durations. Pay particular attention to the clip before the first error and the next clip in the list; if the error occurs on repetition, inspect the final-to-first transition.
- Check media integrity and duration. Look for truncated or damaged files and duration metadata that does not reflect the actual media. Do not add an explicit concat duration unless you independently know the correct duration.
- Test locally before testing live. A clean local concatenation narrows the investigation to live encoding or YouTube ingest; a local boundary glitch points back to the inputs or concat setup.
Build and pace a looping concat input
For a local sequence, create an ffconcat text file with one file directive per clip, in playback order. For example:
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ffconcat version 1.0
file '/media/clip-01.mp4'
file '/media/clip-02.mp4'
file '/media/clip-03.mp4'Then use the concat demuxer as the input. The following is a structural example, not a guaranteed repair command; set the output encoder, bitrate, resolution, and audio options to suit the actual source and YouTube’s current guidance.
ffmpeg -re -stream_loop -1 -f concat -safe 0 -i playlist.ffconcat
-c:v libx264 -c:a aac -f flv "rtmps://YOUR_YOUTUBE_INGEST_URL/YOUR_STREAM_KEY"-f concat -i playlist.ffconcatreads the concat-demuxer list.-stream_loop -1repeats the input indefinitely. It does not normalize the clips.-rereads file input at its native rate rather than sending it as fast as possible. It does not fix timestamps.- Input-scoped options belong before the input they apply to. Keep your actual YouTube stream key private; do not paste it into public logs or share it in a command example.
The example uses -safe 0 to allow absolute paths in a local list. Use it only with a playlist you control, not an untrusted file list. If the files have mismatched stream layouts or encoding parameters, stream copy (-c copy) does not make them equivalent.
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Choose stream copy or normalization based on the files
| Approach | Use it when | Trade-off |
|---|---|---|
| Stream copy | The clips have compatible streams, codecs, and time bases, and their durations are accurate. | Uses fewer resources, but preserves the source packets and cannot reconcile mismatched inputs. |
| Normalize or transcode | The clips have differing stream layouts or encoding parameters, or a compatible stream-copy sequence cannot be produced. | Can make inputs consistent, but continuous encoding costs CPU and a poorly chosen encode can reduce quality. Verify audio/video sync at transitions. |
If metadata duration is wrong but the actual duration is known, the concat script supports a duration directive for each file. If you cannot make the files satisfy the demuxer’s compatibility assumptions, create normalized intermediate files or transcode them to consistent properties, then test the joined result locally.
Change timestamps only for a diagnosed reason
FFmpeg’s setts bitstream filter can assign expressions to packet PTS, DTS, duration, or time base. That describes what the filter can manipulate; it is not a universal repair recipe. The appropriate change depends on the demuxer, codecs, time base, and whether the process copies or encodes streams.
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In particular, setting PTS equal to DTS is documented as not recommended when B-frames are involved. Do not add -copyts, -copytb, -fflags +genpts, or -avoid_negative_ts as generic fixes. Before changing timestamp behavior, identify the affected stream and packets, then check audio/video synchronization and playback across the boundary. Use the help and documentation for the FFmpeg release actually installed; do not treat the historical proposed -force_dts_monotonicity patch as a current supported option.
Check YouTube Live ingest separately
A clean local concat does not prove successful YouTube ingest, and a YouTube ingest problem does not repair a bad local timestamp sequence. YouTube’s current encoder guidance lists RTMP/RTMPS ingest, H.264, H.265 (HEVC), or AV1 video, AAC or MP3 audio, constant bitrate (CBR), frame rates up to 60 fps, and a recommended two-second keyframe interval that should not exceed four seconds. It provides bitrate recommendations by resolution, codec, and frame rate, so select the row for your actual output instead of applying one generic bitrate to every stream. YouTube recommends RTMPS.
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- In YouTube Live Control Room, create or open the live stream and obtain the server URL and stream key from its encoder setup.
- Enter those values in your encoder’s output settings, along with settings appropriate to the intended resolution, codec, frame rate, and bitrate.
- Treat the stream key like a password. If it is exposed, replace or reset it in YouTube’s stream settings.
- Test before going live and monitor stream health and the specific messages in Live Control Room.
Common symptoms and what to check
| Symptom | Likely branch to investigate | Next check |
|---|---|---|
| Error or glitch begins when a particular clip starts | Clip-boundary compatibility, media integrity, or duration | Compare the outgoing and incoming clips’ streams, time bases, and durations; test a local concat. |
| Problem appears only when the playlist returns to its first clip | The last-to-first boundary or behavior of the looped input | Inspect the final and first files and their durations; check the complete log at the transition. |
| Joined local output is clean, but YouTube reports a problem | Live encoder configuration or ingest | Check codec, audio format, CBR, frame rate, keyframe interval, server URL, stream key, and YouTube’s stream-health messages. |
| Audio/video drifts or a gap appears after a timestamp change | The timestamp adjustment may not fit the stream or codec | Revert the change, inspect the stream time bases and durations, and validate synchronization through the boundary. |
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