Can't Play A Reversed .wav File With Mediaplayer

I've created an app that records audio, saves the sample to the sd card then plays it back, using the record and play buttons. I need to reverse this sample. I can do all this and

Solution 1:

The WAV file format includes a 44-byte header chunk. Most WAV files consist of this 44 byte header, followed by the actual sample data. So, to reverse a WAV file, you should first copy the 44 byte header from the original file, and then copy the inverted sample data from the original after the header. If you just reverse the byte order of the original entire file, it definitely won't work. It also won't work if you copy the header and then reverse the byte order of the remainder of the file (actually it will sort of work, except what you get will be just noise). You actually need to reverse the frames, where the frame size is dependent on the bytes-per-sample and whether the file is stereo or mono (for example, if the file is stereo and 2 bytes per sample, then each frame is 4 bytes).

Note that not all WAV files are "canonical" like this. WAV files are actually a variant of RIFF files, so technically you need much more complicated code to find the various parts of the header and sample data within the original file. However, most WAV files are just the header followed by the samples (and this will certainly be true if you're recording the audio yourself), in which case you can save yourself a lot of work.

Joe Cullity's link is a good description of the WAV file format.

Solution 2:

There is a good description of the .WAV header at link text

Also note that all data in the file is stored as Little Endian order (low order byte of 1 multi byte number is stored at the lowest address....) so you can't just reverse the bytes. you need to see how many bytes wide each sample is, (usually 16, but check the header) and reverse them in chunks of that size

Solution 3:

I'm pretty sure that you're right and that the problem is that you can't just reverse the bytes in the file to reverse the waveform because you're destroying header information. You should try to see if there's a good library out there to do this, since I have little experience working with .wav files.