Determinism issues possibly due to frontend issues

[nattthebear]

This is a lot of tickets, and by gathering them all together here I'm not stating with certainty that all of them are the same issue, or even that all of them are frontend issues. The truth is always more nuanced than that. But this is a lot of issues, all of them recently created. A small number of users reported most of them, suggesting that those users may inadvertently "trigger" things with their style of usage. Some of the referenced cores haven't seen any major work in a long time, so it seems unlikely that those cores are broken.

I want to investigate and fix core determinism issues, but the water is very muddy right now.

Possible desyncs caused by frontend:

• [TAStudio] Switching consoles throws input display exception #3417
  • REPRO'D AND FIXED!
• Bizhawk desync issue (Playback of a tas project is totally random) #2738
  • REPRO'D AND FIXED!
• TAStudio Desync - 2.5.2 #2560
  • REPRO'D AND FIXED!
• The recording and playing of TAS in GBA and GB are not synchronized #2523
  • not enough detail
• MAMEHawk: playing movie under file>movie>play movie desynchronized for some games #2496
  • not enough detail, leaving open because there might be a real bug in MAME core
• mGBA: Woody Woodpecker in Crazy Castle 5 desynchronization  #2473
  • mGBA in 2.4.2, waiting on user outdated build
• BSNES: Actraiser desynchronization #2469
  • movie uses autofire, but leaving open due to 'randomizeinitialstate' discussion new issue opened for randomize, this one is closed
• Input movie desynchronizations #2470
  • many NES + 2 SNES + 1 PSX, user is adamant repro is easy and never provided a video recording when asked movies used autofire in effected builds, fixed
• Movie "record from now" desyncs with savestates #2438
  • NesHawk in 2.6, not TAStudio but "Record From: Now" autofire and SRAM issues in effected builds, fixed
• GBHawk: Totsugeki! Ponkotsu Tank desynchronization #2406, GBHawk: Soreyuke! Speedy Gonzales desynchronization #2452
  • GBHawk movies used autofire in effected builds, fixed
• sram file not detected/used and desync #2388
  • REPRO'D AND FIXED!
• turning on "Auto-load Last state" breaks movie recording/playback #2384
  • adelikat said no-one uses this feature anyway Fixed
• Octoshock
  • PSX - How to trigger a desync every single time, step by step #3090
    • 2.8 dev, w/ TAStudio
  • MovieSaveRam ignored after rewinding the TAS #2849
    • 2.6.3 dev, w/ TAStudio
  • Regular Desyncing issues #2830
    • 2.6.2, w/o TAStudio
  • Replicable desyncs on Bugs Bunny Lost in Time NTSC-U / PAL #2743
    • w/ TAStudio
  • Frequent PSX Desyncs Issues (CTR NTSC-U / -J / PAL) #2598
    • maybe w/o TAStudio
  • PSX Movie Desyncs but syncs if you playback little earlier frame #2540
    • w/ TAStudio
  • Savestate loading is nondeterministic in Octoshock #2214
    • maybe w/o TAStudio

Planned improvements to file management in frontend:

• States can be loaded across movies with the same name but in different locations #2484
• TAStudio should use separate files from normal play for SaveRAM etc. #2437
• Always be recording a movie #3061

Desyncs through unrelated, but known, causes:

• No warning or error is given when playing back a movie with a different firmware than it was recorded with #2498

[YoshiRulz]

This makes a lot of sense actually. I think #2484 should be priority number 1 for 2.7.

edit: s/2.6.1/2.7/, can't always get what you want
edit edit: sadly this isn't going to make 2.8 and I doubt it'll make 2.8.1