[ARC Tech-109]

AFM audio was native to the 8 MM video format as Sony used the full width of the tape for recording. It was adopted from the BetaHiFi method and used a multiplexing method similar to BetaHiFi of two carriers split between the A & B heads then added stereo and PCM as the technology matured.
It was a shrunk down beta wrap that was conceived as a consumer camcorder format. People wanted smaller and easier to use models and the Sony BetaMovie was all but dead, VHS-C was cumbersome with the adapter and those had an appetite.
There's some confusion on who the father is of the 8 MM video format, I've seen claims that Kodak was the first and Matsushita was the OEM of those however I did have my hands on a Sony brand portable at the start of my freshman year 1984 at Audio Innovations... a pivotal moment for a techno nerd. There's also a Sony pro model camcorder and docking deck that was used for news gathering however despite the high luma resolution of the format it was still a color under system and yielded about 30 lines of color resolution where BetacamSP was 120 lines color and 330 lines luma with a far better timebase stability. The Digital 8 was strictly a consumer format and uses the same 4:1:1 sampling of DV, it was also adapted to be a data backup format by Exabyte.
The PCM side was not as good as VHS HiFi despite the hoopla. It had a limited high end, I've never seen a deck that could do a digital audio dub due to the way everything is recorded without a way to store the video field and writing new information. This is native to the digital betacam format where everything is segmented and the drum runs at some 5400 RPM. The professional Tascam DA88 also has a punch in/out recording method for each of the 8 channels and it records 16 bits at 44.1 & 48 khz using a Hi8 tape. PCM was introduced in 1985 and I have a demo tape from that era of various music videos.
180 min tapes were probably for the PAL markets, the tape there runs slightly slower than NTSC making a 150 run for 180 and marked as such. I'm not sure about the tape lengths at the start.
IMO it was a good format for the day but it never had the market saturation of VHS, people didn't want two different formats and while Sony did market some very nice home Hi8 VCRs it never caught on, Blockbuster didn't rent Hi8 movies. VHS was cheap and it fit the budget with the perpetual flashing 12:00 on the front.