Convert PART to MP3

A device, media player, or audio editor may require a finished .mp3 file after a download has been interrupted and left as .part. The download usually must be completed first; converting the incomplete file cannot recreate missing audio data.

What the PART format is

.part is a temporary filename, not an audio format. Web browsers such as Mozilla Firefox and download managers use it while a file is downloading; Chromium-based browsers commonly use .crdownload instead. A PART file can contain an incomplete MP3, video, archive, document, or another file type, so the extension does not identify its contents.

A paused or failed download may retain its PART file so the creating program can resume it. Leave the file with that program and resume or restart the download rather than opening it in a converter.

What the MP3 format is

MP3 is a lossy, compressed audio format supported by phones, cars, media players, operating systems, and most editing software. It produces much smaller files than uncompressed WAV or AIFF by removing audio information that is considered less audible.

MP3 is suitable for playback, sharing, and portable storage. It is not an ideal editing master: encoding already compressed audio again can introduce additional quality loss.

How to convert a completed PART file to MP3

1. Resume or finish the download in the browser or application that created the file. A successful completion normally removes .part and restores the original filename. If the application reports an error, download the source again; a converter cannot fill missing sections.
2. If the program says the download is complete but the filename still ends in .part, make a copy and determine the intended original type from the download page, source application, or filename. Rename the copy only to that known extension. Do not blindly rename it to .mp3.
3. Test the completed file with FFmpeg's inspection tool:

ffprobe -v error -show_format -show_streams "input.part"

If the output shows an audio stream, convert it with FFmpeg:

ffmpeg -i "input.part" -map_metadata 0 -vn -codec:a libmp3lame -q:a 2 "output.mp3"

-q:a 2 requests variable-bitrate MP3 encoding at roughly 190 kbps. For a fixed bitrate preferred by some older devices, use:

ffmpeg -i "input.part" -map_metadata 0 -vn -codec:a libmp3lame -b:a 192k "output.mp3"

FFmpeg examines the file's actual data rather than relying on its extension. If the input is already a valid MP3, do not re-encode it unnecessarily; after confirming its type, copy or rename it to an .mp3 filename instead.

For a graphical desktop workflow, open the completed audio in Audacity and choose File → Export Audio, select MP3, and choose the bitrate. Audacity may need its FFmpeg support installed to import some formats. Exporting an MP3 source as MP3 performs another lossy encode.

Reputable online services such as CloudConvert and Zamzar can convert a completed, valid audio file: upload it, choose MP3, set the available quality option, and download the result. They cannot repair an unfinished PART file. Do not upload confidential recordings or copyrighted material when the service's storage and processing terms are unsuitable.

Quality and compatibility limits

Use the original completed file as the conversion source whenever possible. Converting from WAV, FLAC, or another lossless format preserves more quality than converting from an existing lossy format. MP3 export can also omit or alter metadata, cover art, chapters, and multiple audio streams.

If ffprobe finds no audio stream, the file is likely incomplete, corrupted, or not audio. Renaming the extension changes only the filename; it does not convert the data or recover absent content.