1Upload every file you want combined — at least two of them.
2Drag the uploaded items into the order you want; the order is taken from the list, not from the filenames.
3Start the merge, which joins matching inputs without re-encoding them and reconciles mismatched ones exactly once.
4Download the single combined Audio file.
Merge Audio FAQ
Is the merge lossless?
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It is whenever the inputs already agree — the encoded data is copied straight through. It stops being lossless only when the inputs disagree and something has to be re-encoded to make them compatible, and even then it is one pass, not one per file.
How does Merge Audio join the files together?
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Concretely, matching inputs are concatenated by copying encoded frames and mismatched ones are normalised once, so the join is as cheap as the source material allows. Upload everything you want combined and the result comes back as a single file.
Anything specific to Audio when merging?
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Yes — the codec is detected from the stream, so a mislabelled extension does not derail the job. That is worth checking when the inputs did not all come from the same source.
How many files can I combine at once?
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On the free tier a merge accepts two files at a time, which is deliberately higher than the single-file limit on other tools because merging one file is meaningless. A pass removes the cap entirely.
Which audio formats does Merge Audio accept?
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MP3, WAV, AAC, M4A, FLAC, OGG, Opus, WMA and AIFF. Codecs are detected from the stream rather than the extension, so a mislabelled file still works and a mixed batch is handled per file.
Is there a file size limit on Merge Audio?
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Yes: free accounts process audio up to 200 MB per file whichever codec you brought; ffmpeg handles the decode and encode. In practice that limit only bites on uncompressed WAV; a compressed file of the same length is nowhere near it.
Will Merge Audio lower the quality of my audio files?
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It depends on the source. Lossless input (WAV, FLAC, AIFF) is edited sample-exactly and loses nothing. Lossy input has already discarded detail once, so where the job can be done by copying the encoded stream rather than re-encoding it, that is the path taken.
Can I run Merge Audio on several audio files at once?
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Yes. The set queues in parallel with identical settings, which is how you process an album or a podcast back catalogue without repeating yourself.
Why does a EPUB site host Merge Audio?
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EPUB.to is built around the open eBook format — XHTML in a zip, reflowable by design, and readable on hardware nobody has thought about the layout for. A book is a zip full of markup, images and fonts, so almost every job people bring to an eBook site is really a job on one of those things. Merge Audio runs on the same upload and the same account as the conversions because that is where it is needed.
What should I do with the result once Merge Audio is finished?
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The converter on this site moves books between EPUB, MOBI, AZW3, PDF and DOCX, so a title ends up on whatever hardware is actually going to read it. Doing that after Merge Audio means the conversion is made from the version you settled on, not from the one you were still fixing.
Is Merge Audio here the same tool the sibling sites run?
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The engines are shared — the same toolchain, the same workers, the same limits. What a EPUB site adds is a view on reflow: which of these operations a reflowable book genuinely supports, and which ones only make sense on the fixed-layout media inside it. It also starts from one fact about the format this site is named after: the book is a zip of XHTML with a manifest, so the text costs almost nothing and every decision that matters is about the embedded images and font subsets.
Do I need an account, and does anything get kept?
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No account, and nothing is kept: uploads are deleted from the workers shortly after the job finishes, nothing is read and nothing is indexed. Free accounts exist for history and batch size, not for access.
