Overview

Welcome to the Freesound APIv2 documentation!

With the Freesound APIv2 you can browse, search, and retrieve information about Freesound users, packs, and the sounds themselves of course. You can find similar sounds to a given target (based on content analysis) and retrieve automatically extracted features from audio files, as well as perform advanced queries combining content analysis features and other metadata (tags, etc...). With the Freesound APIv2, you can also upload, comment, rate and bookmark sounds!

NOTE: Some of the examples in the API docummentation use the multi-platform command-line tool curl (http://curl.haxx.se). If you do not have curl installed, we recommend you to install it as it will help you learning how to use the Freesound API.

Authentication

In order to start using APIv2 you’ll need an API credential that you can request in http://www.freesound.org/apiv2/apply. Basic API calls can be authenticated using a typical api key mechanism in which you’ll need to add the key given with your APIv2 credential into every request you make. You’ll need to add the key as a token request parameter. For example:

curl "http://www.freesound.org/apiv2/search/text/?query=piano&token=YOUR_API_KEY"

However, there are some APIv2 resources that require the use of OAuth2 authentication. Please, read the Authentication docs for a complete description of both authentication methods and how to use them.

Resources

The Freesound APIv2 has plenty of resources allowing you to do a lot of stuff with Freesound data. Here we just give an overview of the available resources, you will find the full documentation in Resources.

Searching

There are several ways in which you can search sounds using the Freesound APIv2. The most basic one is using the Text Search resource which allows you to define some query terms and other parameters to filter query results. As a quick example, the following request would return all sorts of dog sounds:

curl "http://www.freesound.org/apiv2/search/text/?query=dogs&token=YOUR_API_KEY"

Besides text-search, you can also use the Content Search resource to perform queries and define filters based on audio features (descriptors) rather than tags and textual metadata. That means that you can retrieve sounds that, for example, have a particular pitch or bpm. These queries may include almost any of the audio features listed in Analysis Descriptor Documentation. Note however that these features are automatically extracted and might not be always accurate. As a quick example, you can retrieve sounds that feature a particular pitch mean as follows:

curl "http://www.freesound.org/apiv2/search/content/?descriptors_filter=lowlevel.pitch.mean:[219.9 TO 220.1]"

Furthermore, you can combine both textual and content based search strategies using the Combined Search resource. This is useful as it allows you to specify a query or filter both in terms of metadata and audio features. For example, you could search for loops with a particular bpm using the following query:

curl "http://www.freesound.org/apiv2/search/combined/?filter=tag:loop&descriptors_filter=rhythm.bpm:[119 TO 121]"

Downloading sounds

The Freesound APIv2 allows you to downloads sounds from Freesound. There are two ways in which you can download sounds. The first one is to download the original file that was uploaded to Freesound for a particular sound. You can do that using the Download Sound (OAuth2 required) resource. This resource allows you to retrieve the file in its maximum quality, but the format depends on the original format with which the sound was uploaded (it can be .wav, .aif, .flac, .ogg or .mp3). This means that the weight of the sound can vary a lot depending on the format. Note that, unlike in the previous version of the API, this resource requires to use the OAuth2 authentication strategy (see Authentication).

The second way in which you can download sounds is by accessing their previews. When sounds are uploaded to Freesound we automatically generate .ogg and .mp3 versions for each one with different qualities. We call these versions previews. Using the Sound Instance resource (or any resource that returns a list of sounds), it is possible to obtain the urls for retrieving sound previews. In general, using previews is much more faster than downloading sounds in their original quality, and allows your application to retrieve sounds with an unified format. Retrieving previews does not require OAuth2 authentication.

Uploading sounds

APIv2 also allows you to upload sounds to Freesound! Sounds are uploaded by providing an audio file and some metadata which we call sound description. The minimum sound description consists in a list of tags, a textual description for the sound and the license with which the sound should be released. You can upload and describe sounds using the Upload Sound (OAuth2 required) resource (requires OAuth2). Alternatively, you can simply upload an audio file using the Upload Sound (OAuth2 required) resource, and later describe it using the Describe Sound (OAuth2 required) resource.

Take into account that all sounds in Freesound are automatically processed and manually moderated (including sounds uploaded using the APIv2). This means that after sounds are uploaded and described, they still need to be processed and moderated before they appear in the Freesound web and can be further used in the APIv2. Processing is an automatic step that is almost instantaneous, but moderation is done manually by a team of people and might take some days. The Freesound APIv2 provides a resource, Pending Uploads (OAuth2 required), to keep track of the status of uploaded files.

More stuff...

Besides searching and uploading/downloading sounds, the APIv2 also allows you retrieve information about sound analysis, similar sounds, sound packs, users, bookmarks... Check the Resources page for a complete list and description of resources!

Browseable API

Freesound APIv2 includes a browseable API which renders responses in nice html when accessing them with your browser. Using the browseable api will allow you to quickly experiment with resources and learn to use Freesound APIv2. You can start using the browseable api pointing your browser to http://www.freesound.org/apiv2 . Note that the browseable API authenticates yourself with standard session authentication (instead of token or OAuth2), so you’ll need to login into Freesound.

POST request content types

In POST requests, we recommend to use multipart/form-data content-type and set the header accordingly. For requests that do not include file uploads, we do also support application/json and application/x-www-form-urlencoded content-types.

Response Format

The format of the response can be specified in the request and can be one of JSON, XML and YAML. We recommend using JSON, as this is currently the only response format we actively test.

To specify the desired response format use a format request parameter. Specify the desired format in lowercase letters as follows:

http://www.freesound.org/apiv2/sounds/1234/?format=json
http://www.freesound.org/apiv2/sounds/1234/?format=xml
http://www.freesound.org/apiv2/sounds/1234/?format=yaml

If the format is not specified, it will be automatically determined in the content-negotation phase, typically defaulting to json.

Errors

If your requests are correctly processed and no errors occur, the APIv2 will return a response with a 200 OK status code. However, if something goes wrong in your requests, the Freesound APIv2 will return error messages which can include the following status codes:

HTTP code Explanation
400 Bad request The request was unsuccessful because the request is missing parameters or parameters are not properly formatted.
401 Unauthorized The credentials you provided are invalid.
403 Forbidden Mainly returned when resources that require https are accessed with plain http requests.
404 Not found The information that the request is trying to access does not exist.
405 Method not allowed The current request method (generally GET or POST) is not supported by the resource.
409 Conflict The request is valid but it can not be processed for some reason detailed in the response.
429 Too many requests The request was throttled because of exceeding requst limit rates (see Throttling).
5xx An error on our part, hopefully you will see few of these.

All error responses consist of a dictionary with a detail field that describes the error. Make sure to check the contents of that field to better understand the nature of the error, particularly in 400 Bad request responses.

Throttling

The usage of the APIv2 is limited to certain usage rates. The standard usage rate is set to 60 requests per minute and 5000 requests per day. Resources including uploading, describing, commenting, rating and bookmarking sounds have a more strict rate of 30 requests per minute and 500 requests per day.

If a request is throttled, the APIv2 will return a 429 Too many requests response error with a detail field indicating which rate limit has been exceeded.

Although we have set the default usage limits so that they should be enough for most applications, if these usage limits are not enough for you, please contact Freesound administrators at mtg at upf.edu to request more permissive limits.

More help

If you need more help after reading these documents, want to stay up to date on any changes or future features of the Freesound APIv2, or if you would like to request more features for the API, please contact us using our google group:

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