Merge "MediaCodec: Fix documentation on float raw audio buffers" into qt-dev am: 2d87d7a4

 <h4>Raw Audio Buffers</h4>

 <h4>Raw Audio Buffers</h4>

 <p>

 <p>

 Raw audio buffers contain entire frames of PCM audio data, which is one sample for each channel

 Raw audio buffers contain entire frames of PCM audio data, which is one sample for each channel

 in channel order. Each sample is a {@linkplain AudioFormat#ENCODING_PCM_16BIT 16-bit signed

 in channel order. Each PCM audio sample is either a 16 bit signed integer or a float,

 integer in native byte order}.

 in native byte order.

 Raw audio buffers in the float PCM encoding are only possible

 if the MediaFormat's {@linkplain MediaFormat#KEY_PCM_ENCODING}

 is set to {@linkplain AudioFormat#ENCODING_PCM_FLOAT} during MediaCodec

 {@link #configure configure(…)}

 and confirmed by {@link #getOutputFormat} for decoders

 or {@link #getInputFormat} for encoders.

 A sample method to check for float PCM in the MediaFormat is as follows:

 <pre class=prettyprint>

 <pre class=prettyprint>

 static boolean isPcmFloat(MediaFormat format) {

   return format.getInteger(MediaFormat.KEY_PCM_ENCODING, AudioFormat.ENCODING_PCM_16BIT)

       == AudioFormat.ENCODING_PCM_FLOAT;

 }</pre>

 In order to extract, in a short array,

 one channel of a buffer containing 16 bit signed integer audio data,

 the following code may be used:

 <pre class=prettyprint>

 // Assumes the buffer PCM encoding is 16 bit.

 short[] getSamplesForChannel(MediaCodec codec, int bufferId, int channelIx) {

 short[] getSamplesForChannel(MediaCodec codec, int bufferId, int channelIx) {

   ByteBuffer outputBuffer = codec.getOutputBuffer(bufferId);

   ByteBuffer outputBuffer = codec.getOutputBuffer(bufferId);

   MediaFormat format = codec.getOutputFormat(bufferId);

   MediaFormat format = codec.getOutputFormat(bufferId);

   ShortBuffer samples = outputBuffer.order(ByteOrder.nativeOrder()).asShortBuffer();

   ShortBuffer samples = outputBuffer.order(ByteOrder.nativeOrder()).asShortBuffer();

   int numChannels = formet.getInteger(MediaFormat.KEY_CHANNEL_COUNT);

   int numChannels = format.getInteger(MediaFormat.KEY_CHANNEL_COUNT);

   if (channelIx < 0 || channelIx >= numChannels) {

   if (channelIx < 0 || channelIx >= numChannels) {

     return null;

     return null;

   }

   }