1 VAS Intro

1.1 Brief Introduction

At present, the common audio encapsulation formats in media streaming are MP3, AAC, WMA, OGG, etc. Each encapsulation method has a unique characteristic, and it is applied in different business scenarios.

In order to help our customers to reduce technical investment and adapt to different application scenarios and different terminals, CDNetworks has rolled out audio transcoding feature, which supports any input-and-output in MP3, AAC, WMA and other audio encapsulation formats.

Audio transcoding includes the following features: audio format conversion, audio trans-rating, audio channel and sampling rate setting.

1.2 Applicable Product Line

• Media Acceleration

1.3 Application Scenarios

• It applicable to the scenario that convert the audio input in multiple formats into audio output in mp3 formats. So, it is applicable to cross-platform, cross-terminal playback;
• It is applicable to the scenario that that input is video file or audio file, and the output is audio only with audio transcoding configured. It applicable to the audio playback in weak network.
• Insert audio clip to protect copyrights. For example, the customer has the demand to insert a clip which could be an advertisement audio or the audio that marks identity (it is kind of watermark). Under normal playing scenarios, when the audio file is requested by the original APP or player, the clip content will not be played; and if there is hotlinking, in most cases the audio file is requested by 3rd party player, the full audio file (with the clip inserted) will be played. CDNetworks offers service of inserting the audio clip that marks identity.
• Volume Settings to ensure that the volume is consistent when playing different episodes of a series. Transcoding is required when writing the volume parameters into audio file, and the parameters should be complied to a unified standard and recognizable to player, so they will be read by the player and the consistency of volume is guaranteed for different files playback.

2 Feature Detail

Audio transcoding supports common video/audio encapsulation formats and encoding formats:
(1) Video formats: MP4, FLV, M3U8, TS, MKV, MOV, WMV, AVI, VP8, VP9, RealVideo, Windows Media Video, etc.
(2) Audio formats: AAC, AC-3, MP1, MP2, MP3, PCM, RealAudio, Windows Media Audio (WMA), OGG, etc.
(3) Encoding Formats: H.265, H.264, H.263, MPEG, etc.

2.1 Working Process

(1) The customer calls the cloud storage API to upload the audio file and assigns a transcoding instruction;
(2) After receiving the transcoding task, the cloud storage assembles customer transcoding instructions and sends them to the cloud transcoding;
(3) Cloud transcoding fetches the audio file from the cloud storage for transcoding operation, and uploads the processed audio file to the cloud storage;
(4) Cloud storage notifies the customer of the transcoded video address through API callback;
(5~8) For the customers who have enable CDN acceleration service, their users will utilize the audio address that the cloud storage sends to customer, to initiate requests to CDN PoPs and receive response.

2.2 Instruction

When customers upload a video file or an audio file, they will be configured with the transcoding parameters at one time, needless to call the API separately.

When the customers have not enabled the audio transcoding service, the audio transcoding parameters will be invalid even if they are uploaded though the API.

The audio transcoding feature can be used together with the VoD video transcoding, VoD transmuxing and VoD File processing, that is to say, multiple features can be realized through single API command concatenation.

2.3 Interface Description

2.3.1 Request Description

POST /fops
Host:
Authorization:

AK, SK and host（Management domain） could be obtained from CDNetworks Nova as followed:

2.3.2 Parameter Description

Request parameters are organized in the following format, submitted and shown in request content:

bucket=<Urlsafe_Base64_Encoded_Bucket>&key=<Urlsafe_Base64_Encoded_Key>&fops=<Urlsafe_Base64_Encoded_Fops>&notifyURL=<Urlsafe_Base64_Encoded_PersistentNotifyUrl>&force=&separate=

Fill the parameters of audio transcoding in fops according to actual requirements. Multiple operations can be spliced together and be executed as fops parameter. In other word, fops= Urlsafe_Base64_Encode (operation 1; operation 2; …).

Filling in parameters in the following format, and fill the value following Urlsafe_Base64_Encode in the fops parameter:

/
/acodec/
/aq/
/ab/
/ar/
/ac/
/an/
/vn/
|saveas/<encode(bucket:filekey)>

2.3.3 Response Description

• If the request succeeds, return the Json character string as follows:

{ “persistentId”: }

• If the request fails, return the Json character string as follows:

{
“code”: “”,
“message”: “”
}