ACT

• Samples: http://samples.mplayerhq.hu/A-codecs/act/
• Working decoder: http://www.netac.com/Download/C635/C635%20Driver&Tools.zip

ACT is used as codec in is used by Chinese-made portable MP3 players when recording from the internal microphone.

ACT is a low complexity speech compression codec. There are 3 different ways to record to this codec from a player.

• Fine Rec
• Long Rec
• Long Vox, in this mode the player will just record if there is anything to record.

It is unknown if there are several bitstream formats. With the software that are supposed to convert the files to wav audio are 2 or 3 command line programs. When running one the work G729 is mentioned and the bitrate 4,4k. So an initial guess is that the 3 recording formats are 8kbits, 4.4kbits and 4.4kbits with voice activation. And that the codec actually is G729

ACT File Format

The first 512 bytes seem to be a regular RIFF header. The function at 0x00401000 is in the call tree when converting act files.