How to play MP3 audio buffers

[shah...@essential.com]

Hi,

I am developing a C++ only library (no java) using the NDK audio library. One of the functionality I must support is to play MP3 audio buffers (not files, I already done that).

I can't use mediacodec or another open source decoder (just ndk)

This documentation (https://developer.android.com/ndk/guides/audio/opensl-for-android.html) says that I can use the buffer api (Buffer queue data locator) to play PCM data!

How do you go about playing MP3 audio buffers? Can you point me to a documentation or an example code?

Thanks in advance.

Regards, Shahriar

P.S. I know this question has been asked before. But I haven't read a concise answer yet.

[Don Turner]

The NDK has its own extraction and decoding classes: NdkMediaExtractor and NdkMediaCodec.

Docs here: https://developer.android.com/ndk/reference/ndk_media_codec_8h.html

Sample code here: https://github.com/googlesamples/android-ndk/blob/master/native-codec

You'll need to modify the sample code to decode MP3 rather than MP4 (video). 

I would advise against using OpenSL ES for MP3 decoding since this technique has some performance issues. 

[shah...@essential.com]

Hello,

Thanks for the replay. Looking at the header file (NdkMediaExtractor.h) the API supports either a file or url as the source of data (not a buffer):

media_status_t AMediaExtractor_setDataSourceFd(AMediaExtractor*, int fd, off64_t offset, off64_t length);

/**
 * Set the URI from which the extractor will read.
 */
media_status_t AMediaExtractor_setDataSource(AMediaExtractor*, const char *location); // TODO support headers

Shahriar

[Celina Val]

Hi Shahriar,

Did you ever find the solution for your problem? I have the same problem. The API that Don mentioned is only available for the beta ndk-17 and only available for API Level 28+. :(

Thanks,
Celina

[Don Turner]

I'm pretty sure the NDKMediaCodec API is available down to API 16 (if not earlier). It's definitely been around since 2014 https://android.googlesource.com/platform/frameworks/av/+/0c3be875376adaee8d8e8dd917c64926e1513b29/include/ndk/NdkMediaCodec.h

Further to this, I would recommend looking at FFmpeg for the best possible performance. I'm currently working on a sample and documentation for this but rest assured it can be done and provides better performance than the platform APIs. 

[Celina Val]

Hi Don,

Thanks for replying. I believe we were talking about the media extractor API. Extracting the format from a buffer is only available in newer versions.

That said, I decided to use FFmpeg and it works perfectly fine.

Thanks,

Celina

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[Don Turner]

Ah I see, thanks for clarifying. Glad things worked out with FFmpeg. 

Could I ask, is this an open source project you're working on? If so, is the source available somewhere? 

Celina

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