Does converting audio or video lose quality?
Sometimes. The key question is whether the media is merely being repackaged or whether it is being decoded and encoded again.
The quick answer
| Operation | Typical quality effect |
|---|---|
| Lossless → lossless | Can preserve the decoded audio exactly |
| Lossless → lossy | Information is discarded |
| Lossy → lossless | Does not restore information already lost |
| Lossy → lossy | Usually creates another lossy generation |
| Remux | Can preserve the encoded audio/video streams exactly |
Common cases
MP3 to WAV
The file becomes much larger, but the missing information does not return. WAV can preserve the decoded result, not the original pre-MP3 source.
MP3 to FLAC
The new FLAC file is lossless in how it stores its input, but its source was already lossy. “Lossless file” and “lossless provenance” are not the same thing.
WAV or FLAC to MP3
MP3 encoding is lossy, so some information is permanently discarded.
MKV to MP4
If the existing streams are compatible with MP4, they may be remuxed without changing their encoded quality.
Why repeated lossy conversion matters
Lossy encoders make decisions about what information can be discarded. Encoding an already-lossy file gives the next encoder a source that has already been altered, so additional artifacts can accumulate.
When possible, create new lossy copies from a lossless master rather than from another MP3, AAC or lossy video copy.
Conversion is an overloaded word
People often say “convert” for several technically different operations: remuxing, transcoding, resampling, resizing, changing bit depth, changing metadata, or simply renaming a file. These do not have the same quality consequences.
Common confusion
Turning a 128 kbps MP3 into a 320 kbps MP3 creates a larger file, not a reconstruction of the original recording.
A FLAC made from MP3 stores the decoded MP3 result losslessly, including its existing losses.