How to Download Purchased Videos from DMM

2026-01-15 3 min

How to download MP4 format videos locally after purchasing from DMM/Fanza? The official playback options do not include this feature.

The so-called download is merely an encrypted .dcv file, which requires a dedicated player for playback.

So, how can one download a non-encrypted video file? The key still lies in online playback. As long as it can be played on a computer, there must be a way to download it. Through cat-catch, we can discover that the page loads these resources:

However, if you try to download directly, the resulting file cannot be opened:

This is because it uses DASH (Dynamic Adaptive Streaming over HTTP) technology. It does not provide a complete MP4 file directly. Instead, it uses an MPD (Media Presentation Description) file as an index, splitting the video and audio into numerous small .m4s or .ts segments for transmission. Therefore, the core is to capture the MPD link.

However, DASH is just a transmission protocol and is not responsible for encryption. So, we need to further investigate its encryption method. Open the console with F12 and find the “license” related request (https://mlic.dmm.co.jp/drm/clearkey/license):

This is the standard format for ClearKey: JWK (JSON Web Key). It’s very straightforward, directly placing the Key ID (kid) and the Key (k) in an array:

kid is the ID of the key, used to identify which stream this key corresponds to. Convert this base64 to hex: GcbW7lIkNvGzbMd1M5GmfQ -> 19c6d6ee522436f1b36cc7753391a67d.
The k string is very long (about 250+ characters). In standard ClearKey, the key is usually 16 bytes (32 Hex digits). Therefore, such a long k value often indicates that DMM has encrypted the real key in the response, or this is a wrapped token. However, for a large platform like DMM, specific decryption scripts or tools (such as dedicated browser extensions/scripts) are typically required to process this long string to obtain the original 32-digit Hex key. Therefore, it’s very difficult to try and crack the key manually; the best method is still “memory grabbing”.

ClearKey Mechanism: As the name implies, it’s “clear key.” Although the k value might be wrapped in a complex way during transmission (the extremely long string mentioned above), the W3C standard stipulates: The browser must be able to convert this data back into a standard AES-128 key and pass it to the browser’s Content Decryption Module (CDM).

Therefore, the breakthrough point is: The decryption logic for ClearKey is typically completed within the browser’s user-space process. For the decryption engine to work, the system must have a fully decrypted, 16-byte original key present in memory at some moment.

Install the browser extension EME Logger, refresh the website, and you can obtain the corresponding logs:

Save it as a local file, open it, and search for MediaKeySession.update.

These hexadecimal values like 0x7b, 0x22, etc., are actually the ASCII codes for characters in computers. I discovered through conversion that this data block is actually a JSON string.

0x7b = {
0x22 = "
0x6b, 0x65, 0x79, 0x73 = keys

After converting the entire data block, you get the standard JWK (JSON Web Key) structure:

{
    "keys": [
        {
            "kty": "oct",
            "k": "t55KG1DxXXXXXXXXXXXXXX",
            "kid": "GcbW7lIkNvGzbMd1M5XXXX"
        }
    ]
}

Perform Base64URL to Hex conversion again:

KID: GcbW7lIkNvGzbMd1M5GmfQ $\rightarrow$ 19c6d6ee522436f1b36cc7753391a67d

Key: t55KG1DxXXXXXXXXXXXXXX $\rightarrow$ b79e4a1b50f15d75d75d75d75d75d75d

Then we can use N_m3u8DL-RE to download the file:

After the download is complete, the video and audio are automatically merged to get the final file:

Finally, I have integrated this entire workflow into a Chrome extension: Project Link. It contains detailed introductions and the download link. If it helps you, feel free to give it a free Star. The demo video is as follows:

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