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Use FFmpeg’s loudnorm filter with one shared set of target values and separate loudness measurements for every video. For a batch of pre-recorded videos, a two-pass workflow measures each file first, then processes it using those measurements where linear normalization is possible. YouTube’s published upload guidance does not specify a mandatory LUFS target, so treat target values as production choices—not YouTube rules.
Why loudness normalization matters in a video loop
Videos recorded or mastered at different levels can sound uneven when played in sequence. FFmpeg’s loudnorm filter targets integrated loudness and true peak, rather than merely matching sample peaks. For a consistent batch, use the same target settings for every video but measure each file independently. FFmpeg’s filter documentation describes single-pass and double-pass operation for files and livestreams.
Normalization changes the audio signal. If you want to preserve the existing video stream, you can stream-copy the video while filtering and re-encoding the audio; stream-copying video does not copy the audio unchanged.
Choose targets without treating them as YouTube rules
The examples below use I=-16 LUFS, LRA=11 LU, and TP=-1.5 dBTP as illustrative production targets. They are not an official YouTube mastering requirement. YouTube’s upload encoding recommendations specify supported audio formats and sample rate, not a mandatory LUFS target.
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In loudnorm, I is target integrated loudness, LRA is target loudness range, and TP is the true-peak ceiling. FFmpeg documents ranges of -70 to -5 LUFS for I, 1 to 50 LU for LRA, and -9 to 0 dBTP for TP. Its defaults—I=-24, LRA=7, and TP=-2—are filter defaults, not YouTube recommendations. Choose targets appropriate for your material and intended listening; do not assume one number fits every documentary, music bed, interview, or archive recording.
Normalize each video with a two-pass workflow
1. Measure the first file
Run a measurement pass for the audio stream you intend to use. This example selects the first audio stream, prints JSON measurements, and discards the processed output:
ffmpeg -i input.mp4 -map 0:a:0 -af "loudnorm=I=-16:LRA=11:TP=-1.5:print_format=json" -f null -At the end of the output, note input_i, input_lra, input_tp, and input_thresh. These measurements apply to this input file; repeat the measurement for every video. If a file has multiple audio streams, inspect the input and select the intended stream rather than assuming 0:a:0 is correct.
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2. Process that file with its own measurements
Substitute the four measured values for the uppercase placeholders below. They are explanatory placeholders, not literal filter values.
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ffmpeg -i input.mp4 -map 0:v? -map 0:a:0
-af "loudnorm=I=-16:LRA=11:TP=-1.5:measured_I=INPUT_I:measured_LRA=INPUT_LRA:measured_TP=INPUT_TP:measured_thresh=INPUT_THRESH:linear=true"
-c:v copy -c:a aac output.mp4The common targets make the files comparable; the per-file measurements let the filter calculate processing for each source. The example copies any video stream that matches the optional map and encodes the selected audio as AAC. Check FFmpeg’s stream mapping and confirm that the chosen output container and codecs suit your actual inputs. If there is no audio stream, the measurement command cannot run as written; handle that file separately rather than treating silence as a successful measurement.
3. Check whether linear mode was used
Linear normalization is conditional, not guaranteed by linear=true. FFmpeg requires all four measured values; the requested target LRA must not be below the source LRA, and the gain must not push true peak above the target. If those conditions are not met, the filter can revert to dynamic mode. Review FFmpeg’s output and listen to representative passages, especially quiet speech, loud peaks, and transitions between videos.
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Run the same process across a batch
Automate the measurement and processing as two stages for every input: capture that file’s own four measurements, then insert those values into its processing command while keeping the target parameters constant. Do not reuse the first video’s measurements for the rest of the playlist. Preserve a mapping between each filename and its measurement output so values cannot be accidentally assigned to another file.
- Keep target
I,LRA, andTPidentical across the batch unless you deliberately want different loudness treatment. - Measure the final audio mix for each video, not an intermediate track that will later be mixed with narration or music.
- Write processed files to a separate output location and verify filenames and stream mappings before replacing originals.
- After encoding, check playback across file boundaries; normalization cannot correct abrupt edits, inconsistent room tone, or a poorly balanced mix within an individual video.
When one pass is more practical
loudnorm also supports single-pass processing. That can be useful when a preliminary full-file measurement pass is impractical, but it does not provide the same measure-each-file-then-process workflow. FFmpeg notes that dynamic mode upsamples audio to 192 kHz to detect true peaks. If you need a particular output sample rate, set it explicitly with an output option such as -ar or use aresample.
For mono audio intended for stereo playback, assess the dual_mono option. FFmpeg documents it as compensation for perceptual measurement differences in that case; whether it is appropriate depends on how the mono material will be played.
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Check the upload and playback path
YouTube’s upload guidance recommends AAC-LC, Opus, or Eclipsa Audio and a 48 kHz sample rate. Those are upload recommendations, not loudness targets. Its audio troubleshooting guidance warns that poor mono compatibility can degrade or mute audio after stereo-to-mono conversion, so check channel compatibility as well as loudness.
File normalization is distinct from processing during playback. YouTube says Stable volume is on by default when watching videos where available, but it is unavailable for some videos and disabled for YouTube Music and official music videos; see YouTube’s Stable volume information and its audio enhancements page. That playback-side behavior does not replace normalizing your source files for a loop.
Troubleshooting common problems
The output still sounds uneven
Confirm that every file used the same targets and its own measured values. Then listen for differences caused by mix balance, speech-to-music ratios, or edits: integrated loudness normalization does not make unlike mixes perceptually identical in every moment.
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The filter did not stay in linear mode
Check the filter output and measurements. Linear operation can fail when the target LRA is below measured source LRA or the required gain would exceed the true-peak ceiling. The filter may then use dynamic normalization; do not promise an exact linear result merely because the command includes linear=true.
The command reports a stream or mapping error
Inspect the input’s streams and revise -map 0:a:0 if the desired audio is elsewhere. The sample uses optional video mapping (-map 0:v?) and assumes an audio stream exists. Confirm that the output container supports the selected video stream copy and AAC audio.
Audio changes after upload or sounds wrong in mono
Check the encoded file locally, confirm its sample rate and audio codec against YouTube’s upload guidance, and test mono compatibility. A channel-cancellation problem can be exposed when stereo is converted to mono, even when the loudness measurement itself appears reasonable.
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If your normalized videos are ready and the goal is a continuous YouTube loop, StreamNeo can run uploaded videos from the cloud. Upload a recording or build a playlist, add your YouTube stream key once, and go live. Your computer and home connection do not need to stay on; the videos stream as uploaded, up to 4K 60fps, at one flat price per slot, and StreamNeo automatically recovers if YouTube drops the stream. The first day is free with no card. Monthly billing is $9.99 per month. See StreamNeo or start the free first day.
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