Normalize the files to a common audio and video profile before looping them in FFmpeg. MP4 files with different audio codecs, sample rates, or channel layouts are not automatically compatible with FFmpeg’s concat demuxer. Re-encode them to matching streams, create an ffconcat playlist, then send the loop to YouTube using settings that fit your output.
Why different audio formats cause concat problems
An MP4 container does not guarantee that its audio tracks match. One file may contain AAC stereo at 44.1 kHz while another uses a different codec, sample rate, or channel layout. The concat demuxer expects every file to have the same streams, including codecs and time bases; it does not convert mismatches for you. See the FFmpeg concat demuxer documentation.
There are two practical approaches. Use the concat demuxer when the inputs already match, or first normalize them and then use the demuxer. If you want one operation that concatenates and re-encodes, FFmpeg’s FAQ recommends the concat filter when re-encoding is required.
Inspect the files and choose a common profile
Check every input
Run this for each MP4:
ffmpeg -i "input.mp4"Read the output for each video and audio stream: codec, dimensions, frame rate, sample rate, channel layout, stream order, and duration. Decide which video and audio streams you intend to use. If a file has multiple audio tracks, do not assume FFmpeg will select the one you want.
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Choose settings that all clips can share
For a straightforward stereo stream, a common target might be H.264 video at 30 fps and AAC stereo at 44.1 kHz. This is an example profile, not a requirement for every project: select dimensions and frame rate appropriate to the source material and the resolution you plan to stream. YouTube’s current encoder guidance lists AAC or MP3 audio for RTMP/RTMPS, and recommends stereo audio at 44.1 kHz and 128 kbps. Its stated maximum is 60 fps, with a recommended two-second keyframe interval that should not exceed four seconds. Consult YouTube’s live encoder settings for current guidance.
Normalize each MP4 before building the playlist
Re-encode each input to the same video and audio characteristics. The following is a template for sources with a video stream and an audio stream; adjust the mapping and video dimensions to suit your files. Confirm that your FFmpeg build includes libx264.
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ffmpeg -i "input.mp4" -map 0:v:0 -map 0:a:0 -c:v libx264 -r 30 -c:a aac -ar 44100 -ac 2 -b:a 128k "normalized-01.mp4"Repeat for each source, changing the input and output names. This example selects the first video and first audio stream. If a source lacks audio, has multiple audio tracks, or uses an unusual layout, adjust or omit the relevant -map option rather than assuming the same stream index is appropriate. FFmpeg documents stream selection and the -map option; it also notes that option placement matters because options generally apply to the next input or output.
Create and loop an ffconcat playlist
Make a text file named playlist.ffconcat. Its first line must be exactly ffconcat version 1.0 for automatic format recognition, followed by one file directive for each normalized clip:
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ffconcat version 1.0
file 'normalized-01.mp4'
file 'normalized-02.mp4'
file 'normalized-03.mp4'Use paths that resolve from the directory where you run FFmpeg. The concat demuxer adjusts timestamps to place each file after the previous one. If audio and video durations do not line up, boundaries can contain gaps; inaccurate duration metadata can also cause artifacts. The FFmpeg documentation describes the duration directive for cases where stored duration is incorrect.
Send the repeating playlist to YouTube Live
Prepare the YouTube stream
In YouTube Studio, create or select a live stream and obtain its ingest address and stream key. Keep the key private: anyone who has it may be able to send video to your channel. YouTube recommends RTMPS for encryption in transit. Use the ingest URL and key provided for your stream, not a guessed or copied address.
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Run FFmpeg with explicit stream maps
This command is a template, not a universal tested command. Replace the output destination with the RTMP or RTMPS ingest address and stream key supplied by YouTube. Set bitrate, frame rate, resolution, and mapping for your actual playlist and selected stream configuration.
ffmpeg -re -stream_loop -1 -f concat -safe 0 -i playlist.ffconcat -map 0:v:0 -map 0:a:0 -c:v libx264 -r 30 -g 60 -b:v <chosen_video_bitrate> -c:a aac -ar 44100 -ac 2 -b:a 128k -f flv "<YouTube_RTMP_or_RTMPS_ingest_URL_and_key>"-stream_loop -1 repeats the playlist indefinitely; -re reads it at approximately real-time speed. Here -g 60 represents a two-second keyframe interval only at 30 fps. At a different frame rate, choose a GOP length that corresponds to YouTube’s recommended interval. Put output options before the output URL, and avoid publishing your stream key in screenshots, logs, or shared commands.
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Test and monitor
Before relying on the stream, test it with representative motion and audio, then check YouTube Studio’s stream health. YouTube’s guidance recommends testing with audio and representative video movement and monitoring stream health. If YouTube reports a problem, compare the actual encoded output with its current ingest recommendations rather than assuming the source MP4 settings are what is being transmitted.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When to use the concat filter instead
The concat demuxer is useful when the files already have matching streams or have been normalized into matching streams. If you prefer to concatenate and re-encode in one FFmpeg filter graph, use the concat filter; FFmpeg’s FAQ identifies it as the suitable path when re-encoding is needed. The filter approach requires building a graph that accounts for the inputs’ streams and durations, so inspect them and map the intended tracks rather than treating different files as interchangeable.
Troubleshooting
- Concat reports mismatched parameters or produces glitches: ensure the files share codecs, stream layouts, and time bases, or re-encode them to a common profile. Use the concat filter when you need a re-encoding workflow.
- Audio gaps or audio/video drift at clip boundaries: compare stream lengths and duration metadata. The demuxer adjusts timestamps globally, and unequal stream durations can leave gaps. Correct inaccurate duration information where necessary.
- The wrong audio or video track appears: explicitly map the intended streams with
-map, such as-map 0:v:0and-map 0:a:0, after verifying those indices identify the right tracks in your inputs. - YouTube rejects the stream or reports poor health: check the encoded output’s codec, frame rate, keyframe interval, audio settings, and bitrate against YouTube’s current encoder guidance; test and monitor in YouTube Studio.
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