"How do I submit a longplay?" and "What are the rules for Longplays?" are questions often heard on this site recently. Despite Mad-Matt's attempt to explain the rules, these questions still appear. As you might know, the rules have changed quite a bit since the site has first started. I'm Brian0451 and I'm going to try to explain the instructions and rules of how to get a longplay up with current standards.

First, you'll need to go to our Discord server and chat with one of the administrators (ScHlAuChi, MadMatty, Spazbo4 or KAGE-008). Let them know you'd like to be a longplayer and what game you plan on doing. You will then be given instructions on what to do. The basic rundown of what they may say is stated below.

Recording:
Depending on what system the game you would like to record is on, the rules for recording vary. If it's a console, then it is recommended that you use a good capture device capable of capturing in 1080p60 or 720p60, or even 4k60. The Avermedia Live Gamer line is recommended, as well as Elgato.

For PC games, the best way to record is via Fraps or Dxtory. For Fraps, make sure the video settings are set to split on 4GB filesize, lock fps while recording, and force lossless RGB capture. For Dxtory, make sure the video settings are set to record with Lagarith Lossless Codec, synchronize video fps, and file output. The settings for Lagarith will be explained momentarily. The fps option for both programs must be set to what framerate the game runs at. If it's 60, you must record in 60. If 30, you record in 30. Recording in 60 when the game is 30 will double the frames and may cause quality loss.

For emulated games, you need to be using BizHawk for the following systems:
Atari2600/5200/7800
Nintendo Entertainment System
Super Nintendo Entertainment System
Nintendo GameBoy/Color/Advance
Nintendo 64
Coleco
Sony PlayStation
Sega Genesis/CD/32x/Saturn

I may have missed a few, but those are the most commonly used.

There are specific settings for each console you are emulating. They are usually set by default, but to make sure:

PlayStation - PixelPro

Nintendo 64 - Core Type: Pure Interpreter
Rsp Plugin: Z64 HLE Video
Active Video Plugin: Jabo (GLideN64 is better if you have a decent GPU card).
Video Resolution: 320x240 (you may use larger, but not bigger than 640x480)

GameBoy Advance: mGBA

Super Nintendo Entertainment System: BSNES / BSNESv115+

For the other systems, please speak to an admin first.

To record a game with BizHawk, you may NOT use Fraps or Dxtory. You must use its built-in Movie and AVI recorder. You use the movie recorder first. This allows you to play the game like normal and use savestates. Savestates will save your progression where you are at AT THAT MOMENT. I recommend using them often, especially before bosses. When you are done recording the movie, you play it back by clicking "Play Movie". Be sure to pause the emulation before doing so. Then you select "Record AVI/WAV". You may choose AV Writer or FFmpeg writer.

For AV Writer:
Use Lagarith Lossless Codec with the following configurations.

Those configurations must also be used for Dxtory.
You may also use Full Frames (Uncompressed, but that requires a lot of memory.

For FFmpeg Writer:
The recommended codecs are FFV1, AVC1 Lossless, UTVideo or libx264rgb.

IMPORTANT: Sync to Audio must be enabled to preserve the actual console's framerate. If disabled, avi dumping is forced to be at 60fps but this WILL ruin audio pitch to compensate, resulting in an auto-rejected submission.

Once you find a folder to save your video to, un-pause the emulation and let the emulator do its work. Additionally, you may want to go to Config->Speed/Skip->and un-check "Clock Throttle". This will cause BizHawk to run as fast as your PC will let it. Since the AVI writer has auto-speed correction when writing, you won't have to worry about the AVI speeding up or slowing down if you don't have a fast PC. One more thing: click File->Movie->On Movie End-> and check "Pause". This will automatically pause the emulation when the movie is done playing back, so you don't have to worry about it writing more data. Click "Stop AVI/WAV" and it will stop recording.

The Nintendo DS is a hand-held that is (as of this post) not yet supported by BizHawk. For these games, you must either use a 3DS capturing device (talk to Tsunao to get the more specific details), or the emulator DeSmuME. Like BizHawk, DeSmuME has a movie recorder that allows you to record with the use of savestates, and an AVI Writer, which captures every emulated frame. Settings for AVI here are no different from BizHawk. (NOTE: Please use DeSmuME 0.9.9 as the later versions will cause desync issues).
IMPORTANT UPDATE: BizHawk 2.7 and later versions feature a much better DS core that ensures the best compatibility and accuracy. Please use that one for new DS submissions.

Encoding:
The AVI files are not what you submit to Longplays. You must encode them into an .mp4 video before submitting. To do so, you will need MeGUI and AVISynth. Install AVISynth first, then download MeGUI. You will also need the LONGPLAYS profiles found here:

http://realmods.online.fr/MEGUI.7z

Copy-and-paste the folders into the same folder you extracted MeGUI into. Copy-and-paste the AVS Script into the same folder with your AVI files. Open the AVS Script. Change "DirectShowSource" to "AVISource", then place the name of your AVI videos in this format:

AVISource("Video1.avi")+\
AVISource("Video2.avi")+\
AVISource("Video3.avi") adding more lines if necessary.

If your video needs cropping, place a line before the PointResize like the one below:

Crop(X1,X2,Y1,Y2)

Place a "#" in front of PointResize if your video is larger than 6**x4** resolution. If not, leave it be. Replace the subtitles with the game name, your (online longplays) name, and lowercase letters. An example of how they will look is shown below.

Subtitle("Final Fantasy V", first_frame=SubsStart, last_frame=SubsStart+SubsDura, y=340, size=24, text_color=$ffffff, align=2)
Subtitle("Played by Brian0451", first_frame=SubsStart, last_frame=SubsStart+SubsDura+5, y=365, size=24, text_color=$ffffff, align=2)
Subtitle("www.longplays.org", first_frame=SubsStart, last_frame=SubsStart+SubsDura+10, y=390, size=24, text_color=$ffff00, align=2)

Save the script, then drag-and drop it into AVISynth Script in MeGUI. Make sure the profiles are set to both LONGPLAYS for the audio and video output, and the video needs to be set to .mp4 and the audio needs to be set to .m4a. Then click queue for both (audio first, then video). Click on the queue tab, then delete the "mux" job. Wait until the audio is done processing, then click Tools->Muxer->MP4 Muxer. Video input is the .264 file and the audio is the .m4a file. The video output can be saved where you can find it. Now you play the waiting game until all jobs are done. Once the .mp4 video is done encoding, you upload that.

Regarding encoding presets in MeGUI, we recommend using either Very Slow, Slower or Slow depending on the system and/or game. It shouldn't make any difference in quality as long as you use the same CRF value, plus that a Slow profile might help if you're using an old or low-end PC.

Upload:
You will need FileZilla or another FTP manager.
Host: cassiopeia.solit.se
User: upload
Password: upload

Create a folder in the following format:
System - Game Name; example: SNES - Final Fantasy V
The video and .sfv file must be named like this:
SYSTEM_Longplay_-_GAME_NAME_-_REGION (with additional info such as PT, FT, 2P or UL at the end if required).

Drag-and-drop your encoded .mp4 video into your folder. Once uploading, you go back to the Discord chat and tell the admins. They will grant you "longplayer" rights so you may add your longplay to the Submission Status. Follow the simple instructions for submitting. Once that's done, congratulations. You have officially made a longplay.

Factors that may get your video rejected:
If there is quality loss in the video (blur)
Captions (aside from your signature at the beginning) even if it notifies the viewers when and where to skip, captions in video are not allowed. A separate .srt file may be made however.
Recorded or encoded with programs other than the ones mentioned.
Commentary - Longplays are no-commentary at all times. A separate audio track for commentary may be used if desired, but must be kept out of the main video.
Watermarks or custom intros.
Re-scaled or "stretched" videos - keep everything in its original aspect. Don't stretch a 4:3 video to a 16:9 ratio
Again, talk to the admins for more details.

What about other emulators like FCEUX or VBA-RR?

Those aren't allowed as far as I know. Besides, BizHawk supports those games anyway.

MadMatty says FCEUX and VBA-RR ARE OK but Bizhawk is preferred.
Period. Case closed!

Okay then. Use them.

Thanks Brian0451 :D

One thing to be aware when touching the x264 presets: Very Slow is only viable if you're going to encode simpler stuff like NES, Atari 2600 and similar systems. For 90's and 3D systems I recommend using Slower or Slow with CRF of 19-21 and modifying a few parameters such as M.E and b-frames when necessary. This can be useful especially for PCs with an older-gen i3/i5 and even modern Pentiums.

This was very helpful