Can I open an .aria2 file?

An .aria2 file is a binary control metadata file, not a media or document file. It cannot be opened directly in media players. Instead, it accompanies your incomplete target file (e.g. video.mp4 alongside video.mp4.aria2). When the download finishes, aria2 combines the pieces and automatically deletes the .aria2 file.

How do I resume an interrupted .aria2 download?

Keep both the incomplete file and the .aria2 file in the same directory. Then run: aria2c -c (or reload the task in AriaNg / Motrix). aria2 reads the bitfield in the .aria2 file and resumes downloading only the missing chunks.

Is it safe to delete an .aria2 file?

Yes, if you wish to cancel the download and delete the partial file. However, if you want to complete the download, do NOT delete the .aria2 file, as aria2 will lose chunk progress and have to re-download the entire file from 0%.

What is an .aria2 File? How to Open, Resume, and Recover .aria2 Files

An .aria2 file is a lightweight binary control file created automatically by aria2 alongside your download (e.g. archive.zip.aria2 next to archive.zip). It stores the piece bitfield index, file checksums, and transfer byte offsets, enabling parallel multi-connection downloading and instant zero-loss resume after power failure or network interruption.

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1. Chunk Bitfield Index

Tracks which 1MB pieces have been verified on disk and which byte ranges remain uncompleted across up to 16 parallel TCP connections.

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2. Zero-Loss Resumption

If your connection drops or computer reboots, aria2 reads the .aria2 file upon restart and picks up from the exact byte without restarting from 0%.

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3. Automatic Self-Destruct

Once 100% of chunks pass cryptographic SHA-1/MD5 integrity checks, aria2 automatically unlinks and deletes the .aria2 file.

🛠️ Online .aria2 File Header Inspector

Inspect any .aria2 control file locally in your browser. No files are uploaded to any server.

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Drop an .aria2 control file here to inspect

Or click to select from your local drive

Under the Hood: .aria2 Binary Protocol Specification

Byte-by-byte technical layout of the aria2 control file format (Big-Endian byte order).

Byte Offset	Data Type	Field Name	Description
0x00..0x01	uint16_t (2B)	MAGIC_VER	Magic verification bytes: `0x0001` (Version 1).
0x02..0x05	uint32_t (4B)	EXT_FLAGS	Extension flag bitmask (BitTorrent metadata, chunk allocation mode).
0x06..0x1D	bytes[24]	INFO_HASH	20-byte SHA-1 BitTorrent InfoHash or 4-byte HTTP URI identifier hash.
0x1E..0x25	uint64_t (8B)	TOTAL_LENGTH	Total file size in bytes (Big-Endian unsigned 64-bit int).
0x26..0x29	uint32_t (4B)	PIECE_LENGTH	Size of each discrete verification piece (e.g. `1048576` for 1MB).
0x2A..EOF	bitmask[]	PIECE_BITFIELD	Variable-length bitfield: bit `1` = verified on disk, bit `0` = missing chunk.

Step-by-Step Download Recovery Playbook

How to resume, repair, or migrate partial downloads across different scenarios.

Scenario A: Normal Interruption (Power Outage or Network Drop)

Keep both the incomplete file (ubuntu-22.04.iso) and the control file (ubuntu-22.04.iso.aria2) in the same directory, then run:

$aria2c -c -x 16 -s 16 https://releases.ubuntu.com/22.04/ubuntu-22.04.iso

Scenario B: Resuming with a New/Renewed URL (Expired Download Links)

If downloading from cloud hosts (Google Drive, Baidu, 1Fichier) where signed URLs expire after 2 hours:

Obtain the fresh new download URL from your browser.
Rename the partial file and .aria2 file to match the target output name (e.g. target.zip and target.zip.aria2).
Run aria2c -c -o "target.zip" "NEW_FRESH_DOWNLOAD_URL". aria2 re-attaches to the existing bitfield and continues downloading seamlessly!

Scenario C: Force Re-Checking Corrupted Blocks (--check-integrity)

If you suspect a disk crash corrupted chunks:

$aria2c -c --check-integrity=true -s 16 https://example.com/file.tar.gz

Comparison: .aria2 vs Other Incomplete File Formats

How aria2's control file architecture compares to other popular download tools:

Downloader	Temp File Extension	Multi-Connection Support	Bitfield Resume Efficiency
aria2	.aria2 (Control file)	Yes (Up to 16/host)	Exact byte / piece level
Google Chrome / Edge	.crdownload	No (Single Stream)	Linear stream offset only
Mozilla Firefox	.part	No (Single Stream)	Linear stream offset only
Internet Download Manager (IDM)	IDM_*.tmp in AppData	Yes (Up to 32)	Requires proprietary re-assembly

Frequently Asked Questions about .aria2 Files

Why did my video or zip download get saved as .aria2?

It didn't! Your actual file (e.g. movie.mp4) is in the directory alongside movie.mp4.aria2. If you try to open the .mp4 while the .aria2 file is still present, media players will say it is corrupt because some internal chunks have not yet downloaded.

Can I convert an .aria2 file to MP4 or ZIP?

No. You do not convert the .aria2 file — you simply finish the download using aria2, Motrix, or AriaNg. Once finished, the .aria2 file disappears and your original .mp4 or .zip is complete and fully readable.

What happens if I accidentally delete the .aria2 file?

aria2 will lose the bitfield map of completed pieces. If you run the download again, aria2 will start downloading from 0% from scratch.

Why is the .aria2 file not being deleted after 100%?

This typically occurs if BitTorrent seeding is active (aria2 maintains the control file while seeding) or if the file failed checksum verification. Once seeding ends or the task is removed, aria2 cleans it up.