After installing AC3 ACM I see two instances of the codec in VirtualDub 2. One is AC3 ACM which shows the available bitrates, according to the audio input format (such as 48000Hz, 16-bit, Stereo), and the other is AC3 ACM Extensible that only shows the current audio format and a bitrate (such as 48000Hz 16-bit Stereo 188KB/sec). I tried to compress a short video with x265vfw and AC3 ACM Extensible as the audio codec. The file created was too large and an examination with MediaInfo revealed the audio is PCM 16-bit Stereo 1536Kbit/sec with codec ID 00000001-0000-0010-8000-00AA00389B71. What is that? I tried to Google for the codec but I didn't find any useful information. What is AC3 ACM Extensible variant and what is used for? If it produces uncompressed audio why not just select Uncompressed (PCM) in VirtualDub 2?