Atmos Download (Future Feature Request… if possible)

[CoolJoe72]

So it would be awesome to enable the Audible Dolby Atmos option for downloading
I'm not sure if something would need to be added to the api or even what codec format they are using but it seems it can be downloaded in the iOS app and some select android devices.

Digging around the api found this in /1.0/library/B0C66LN3JW but it showed the standard stereo available_codecs

"asset_details": [ "is_spatial": true,"name": "Dolby"]

This is all new to me and I'm not even sure what I'm looking for.

[mkb79]

I'm absolutely low on time this week. But you can try out yourself if you can download and decrypt the atmos audio.

You have to make a POST request to https://api.audible.de/1.0/content/B004UVB7KC/licenserequest. B004UVB7KC must be replaced with your ASIN.

The body for the request above is

{
  "use_adaptive_bit_rate" : true,
  "supported_media_features" : {
    "codecs" : [
      "mp4a.40.2",
      "mp4a.40.42",
      "ec+3"
    ],
    "drm_types" : [
      "Mpeg",
      "Hls",
      "HlsCmaf",
      "FairPlay"
    ]
  },
  "response_groups" : "content_reference,chapter_info,last_position_heard,pdf_url,certificate",
  "consumption_type" : "Streaming",
  "spatial" : true
}

I does not know why the iOS Audible app makes a Streaming request but it download and saves the audio file.

Edit:
The iOS Audible app makes a download request. It looks so

{
  "quality" : "High",
  "response_groups" : "chapter_info,content_reference,last_position_heard,pdf_url",
  "consumption_type" : "Download",
  "supported_media_features" : {
    "codecs" : [
      "mp4a.40.2",
      "mp4a.40.42",
      "ec+3"
    ],
    "drm_types" : [
      "Mpeg",
      "Adrm",
      "FairPlay"
    ]
  },
  "spatial" : true
}

Edit:
In both cases a m3u8 playlist file is provided for downloading using the FairPlay format. After that, the client made a request to https://api.audible.de/1.0/content/B004UVB7KC/drmlicense with a licenseChallenge body to receive the license. I does not know how to decrypt FairPlay DRM.

[CoolJoe72]

Well it was worth a shot, and thank you all your time you put into it. I wasn't expecting a response other than yeah that would be neat and maybe marked as a future option once it was figured out in like 6 months or more.

Looks like I'll have to do some research now I know what direction to go in, when I get some free time.

Thank you.

[devnoname120]

Audible for Android also supports Dolby Atmos. Does it also download a FairPlay format? Because to the best of my knowledge FairPlay is only available on Apple devices so it may be using another (weaker?) DRM.

[mkb79]

@devnoname120

The iOS and Android Audible apps are requesting the same API to make a license request. Therefore, you just have to find out which request body the Android app uses.

For iOS this body is sent:

{
  "quality" : "High",
  "response_groups" : "chapter_info,content_reference,last_position_heard,pdf_url",
  "consumption_type" : "Download",
  "supported_media_features" : {
    "codecs" : [
      "mp4a.40.2",
      "mp4a.40.42",
      "ec+3"
    ],
    "drm_types" : [
      "Mpeg",
      "Adrm",
      "FairPlay"
    ]
  },
  "spatial" : true
}

I do not have an Android device to decrypt the HTTPS traffic sent from the Audible app to the API. So you can using the script below to play around to make a licenserequest and test some codecs and drm_types and check which response the API will give:

import json

from audible import Authenticator, Client


auth_file_path = "..."  # FILL OUT
asin = "..."  # FILL OUT


auth = Authenticator.from_file(auth_file_path)


with Client(auth) as client:

    body = {
        "quality": "High",
        "response_groups": "chapter_info,content_reference,last_position_heard,pdf_url",
        "consumption_type": "Download",
        "supported_media_features": 
            {
                "codecs": [
                    "mp4a.40.2",
                    "mp4a.40.42",
                    "ec+3"
                ],
                "drm_types": [
                    "Mpeg",
                    "Adrm",
                    "FairPlay"
                ]
            },
        "spatial": True
    }

    lr = client.post(
        f"content/{asin}/licenserequest",
        body=body,
    )
    print(json.dumps(lr, indent=4))

Known drm_types are Mpeg, PlayReady, Hls, Dash, FairPlay, Widevine, HlsCmaf, Adrm. And known codecs are ec+3, ac-4, mp4a.40.42, mp4a.40.2. Maybe these helps a little bit?!

[mkb79]

If you remove FairPlay from supported drm_types it will download the book in AAXC (Adrm mode)! I does not know if it using Dolby Atmos. But it uses the mp4a.40.2 codec in booth cases. Tried it with asin 3844535306 and german marketplace .

Edit:
Oh it seams these audiobook is not available in Dolby Atmos.

Edit:
Tried it again with an Atmos title. It will only download with ec+3 and only as FairPlay protected title. Maybe you have more luck.

[devnoname120]

@mkb79 I can't test right now. Did you try with ac-4 and WideVine? This seems to me to be the combo that will most likely work for Android content.

[mkb79]

I've tried it with the codecs ec+3 and ac-4. Drm_types where set to Mpeg, PlayReady, Hls, Dash, Widevine, HlsCmaf, Adrm (only removing FairPlay). This will give me a HTTP 404 error with the message: Unable to retrieve asset details from Sable(AssetInfos), for marketplaceId:AN7V1F1VY261K, asin:B0BGYDYQ38, acr:null, skuLite:OR_ORIG_002267, version:LATEST, aaaClientId:ApolloEnv:AudibleApiExternalRouterService/EU/Prod. Maybe B0BGYDYQ38 is not available on Android devices in Dolby Atmos or they are using some other codecs/drm_types there.

[mkb79]

I've documented some new API endpoints related to the FairPlay DRM.

Steps to download Dolby Atmos titles:

1. The client makes a licenserequest.
2. It receives the response containing a URI to a m3u8 file
3. The client makes multiple GET requests to this URI with the User-Agent: AppleCoreMedia/1.0.0.20G75 (iPhone; U; CPU OS 16_6 like Mac OS X; de_de) and receives content from type `application/vnd.apple.mpegurl
4. Client requests the FairPlay certificate.
5. Client makes a GET request to dpm.demdex.net and receives JSON content (Edit: these step may be not iOS App related)
6. Client make a POST request to drmlicense endpoint
7. The client request build a new URI from the URI from 2 and the filename taken from the m3u8 file and receives the audio/mp4 file.

Edit:
I can’t replay step 6 currently. I does not know how to build the license challenge. If I follow the other steps from above, leaving step 6 out, I receive a 403 status error. So step 6 must be the import part. Maybe the challenge is build using the cert from point 4 and other things?

[mkb79]

@devnoname120
I’ve found out how I can extract the uri from the m3u8 file and download the Dolby Atmos mp4 file. Now I've to find out how to decrypt these file.

[devnoname120]

@mkb79 What's the output of file dolby_atmos_file.mp4?

Note: step 5 is probably irrelevant as dpm.demdex.net is an endpoint used by Adobe Experience Platform Identity Service.

[mkb79]

The m3u8 playlist contains the mp4 file location. With these information you can build the correct URI to the mp4 file. These file must be downloaded using a special Range header specify the byte range like bytes=0-1368458706 for asin B0BGYDYQ38. These audiobook has a size of 1368458706 bytes. If you forgot the Range header I've got an 403 error. So this header is mandatory.

After downloading you have a mp4 file which is encrypted via SAMPLE-AES. Now you need the key for decryption.

[devnoname120]

Here is the full licenserequest JSON body definition on Android:

{
  "supported_media_features" : {
    "drm_types": [
      "adrm",
      "hls",
      "play_ready",
      "mpeg",
      "dash",
      "widevine"
    ],
    "codecs": [
       "mp4a.40.2", // AAC_LC
       "mp4a.40.42", // XHE_AAC
       "ec+3", // EC_PLUS_3
       "ac-4", // AC_4
    ],
    "chapter_titles_type": "flat/tree",
  },
  "spatial" : true, // true/false,
  "consumption_type" : "streaming/download",
  "rights_validation": "ownership/radio/aycl",
  "quality" : "low/normal/high/extreme",
  "version": "[version]",
  "acr": "CR![id_of_28_characters]", // Some kind of id for license?
  "use_adaptive_bit_rate": true, // true/false
  "playback_start_ms": 123,
  "playback_end_ms":  456,
  "response_groups" : "content_reference,chapter_info,pdf_url,last_position_heard,ad_insertion",
  "file_version": "[version]"
}

Not sure whether it differs from the one you see on iOS or not. Just posting this for my future reference I'll dig more into the Atmos stuff on Android.

[mkb79]

Thank you very much. That seams a licenserequest for streaming purposes. use_adaptive_bit_rate is typically for streaming requests. acr is the amazon content reference. This value is unique for each book/asin/codec?/version combination.

Important for me is the response for a download license request for an Dolby Atmos book.

[devnoname120]

Unfortunately I don't have an Android device that supports Dolby Atmos… Neither do I own a Dolby Atmos book.

[devnoname120]

@mkb79 Can you retry with this user agent?

Audible, Android, 3.58.0, samsung, SM-S906B, g0sxeea, 13, 1.0, WIFI

This corresponds to a Samsung Galaxy S22 (it has native Dolby Atmos support).

I cobbled up this user agent by looking at how the Audible app constructs it and filling it with the information I was able to find on the internet. I'm not 100% sure I didn't make any mistakes while building it though.