Write basics of x264 guide (#41)

Author: FichteFoll

SUMMARY.md

@@ -19,6 +19,7 @@
 - [Descaling](encoding/descaling.md)
 - [Resampling](encoding/resampling.md)
 - [Codecs](encoding/video-encoding.md)
+  - [x264](encoding/codecs/x264.md)
 
 
 ## Typesetting

encoding/codecs/x264.md

@@ -0,0 +1,309 @@
+# Encoding with x264
+
+H.264 has been the de facto standard video format
+across the internet for the past decade.
+It is widely supported for playback in all modern browsers
+and many hardware devices such as gaming consoles and phones.
+It provides better video quality at smaller file sizes
+compared to its predecessors.
+
+x264 is a mature, free, open-source encoder
+for the H.264 video format.
+
+
+## Prerequisites
+
+To get started, you'll need two things:
+
+- A video to encode—for the examples,
+  we will pipe in a video from VapourSynth,
+  which you should be able to do
+  if you've been following the previous sections of this guide
+- The x264 encoder
+
+Here's how we get a copy of the x264 encoder:
+
+
+### Windows
+
+Official Windows builds are available
+[here](https://download.videolan.org/pub/x264/binaries/win64/).
+
+
+### Linux/macOS
+
+Generally, x264 will be available
+through your distribution's package manager.
+Here are a few examples:
+
+- **Ubuntu/Debian**: `sudo apt install x264`
+- **Arch Linux**: `sudo pacman -S x264`
+- **macOS**: `brew install x264`
+
+
+## Getting Started
+
+x264 is very configurable,
+and the options may seem overwhelming.
+But you can get started encoding
+by using the presets x264 provides
+and understanding a few basic concepts.
+We'll walk through those concepts
+with the following examples.
+
+
+### Example 1: General-Purpose Encoding
+
+Open up a terminal window,
+and navigate to the folder
+where your VapourSynth script lives.
+Let's run the following command:
+
+```
+vspipe --y4m myvideo.vpy - | x264 --demuxer y4m --preset veryfast --tune animation --crf 24 -o x264output.mkv -
+```
+
+Let's run through what each of these options means:
+
+
+##### `vspipe --y4m myvideo.vpy -`
+
+This portion loads your VapourSynth script
+and pipes it to stdout,
+adding y4m headers that x264 can decode.
+If you use Linux,
+you're probably familiar with how piping works.
+If you're not,
+it's basically a way of chaining two commands together.
+In this case, we want to chain `vspipe`,
+the program that reads VapourSynth scripts,
+with `x264`, our encoder.
+
+
+##### `--demuxer y4m`
+
+This tells x264 that we're providing it with a y4m file.
+This matches up with the `--y4m` flag
+that we gave to the `vspipe` command.
+
+
+##### `--preset veryfast`
+
+x264 has a set of presets
+to switch between faster encoding, or higher quality.
+The full list of presets, from fastest to slowest, is:
+
+1. ultrafast
+1. superfast
+1. veryfast
+1. faster
+1. fast
+1. medium
+1. slow
+1. slower
+1. veryslow
+1. placebo
+
+You will almost never want to use the extreme settings,
+but generally, if you want good quality
+and don't care about how long the encode takes,
+`slower` or `veryslow` are recommended.
+In this example,
+because we are just demonstrating how x264 works,
+we want a fast encode and have chosen `veryfast`.
+
+For the curious,
+you can see a full list of the settings enabled by each preset
+by running `x264 --fullhelp | less` (Linux/Mac)
+or `x264 --fullhelp | more` (Windows).
+However, this probably won't mean much at the moment.
+Don't worry,
+this page will explain later
+what all of those settings mean.
+
+*Disclaimer:
+x264's `fullhelp` is not guaranteed to be up-to-date.*
+
+
+##### `--tune animation`
+
+Beyond the preset chosen,
+x264 allows us to further tune the encoding settings
+for the type of content we're working with.
+The following tunings are generally the most useful:
+
+- `film`: Recommended for live action videos.
+- `animation`: Recommended for anime or cartoons with flat textures.
+  For 3D animation (e.g. Pixar movies),
+  you may find better results with `film`.
+- `grain`: Recommended for particularly grainy films.
+
+You don't need to use a tuning,
+but it generally helps
+to produce a better-looking video.
+
+
+##### `--crf 24`
+
+CRF is a constant-quality, 1-pass encoding mode.
+In layman's terms,
+this means that we don't need the output to meet a specific filesize,
+we just want the output to meet a certain quality level.
+CRF ranges from 0 to 51 (for 8-bit encoding),
+with 0 being the best quality
+and 51 being the smallest filesize,
+but there is a certain range of CRF settings
+that are generally most useful.
+Here are some guidelines:
+
+- CRF 13: This is considered visually lossless to videophiles.
+  This can produce rather large files,
+  but is a good choice if you want high quality videos.
+  Some fansubbing groups use this for Blu-ray encodes.
+- CRF 16-18: This is considered visually lossless to most viewers,
+  and leans toward high quality
+  while still providing a reasonable filesize.
+  This is a typical range for fansub encodes.
+- CRF 21-24: This provides a good balance between quality and filesize.
+  Some quality loss becomes visible,
+  but this is generally a good choice
+  where filesize becomes a concern,
+  such as for videos viewed over the internet.
+- CRF 26-30: This prioritizes filesize,
+  and quality loss becomes more obvious.
+  It is generally not recommended to go higher than CRF 30
+  in any real-world encoding scenario,
+  unless you want your videos to look like they were made for dial-up.
+
+
+##### `-o x264output.mkv -`
+
+This last portion tells which files to use for the input and output.
+We use `-o` to tell which filename to write the encoded file to.
+In this case, x264 will write a file at `x264output.mkv`
+in the current directory.
+
+The last argument we are passing to x264 is the input file.
+In this case, we pass `-` for the input file,
+which tells x264 to use the piped output from vspipe.
+The input argument is the only positional argument,
+so it does not need to be last;
+x264 will recognize it
+as the only argument without a `--` flag before it.
+
+
+### Example 2: Targeted File Size
+
+For the next example,
+let's say we want to make sure our encode
+fits onto a single 4.7GB DVD.
+How would we do that in x264?
+
+First, we'll need to figure out
+what bitrate our encode should be,
+in **kilobits per second**.
+This means we'll need to know a couple of things:
+
+- The length of our video, in seconds.
+  For this example,
+  let's say our movie is 2 hours (120 minutes) long.
+  We'll convert that to seconds:
+  120 minutes \* 60 minutes/second = **7200 seconds**.
+- Our target filesize.
+  We know that this is 4.7GB,
+  but we need to convert it to kilobits.
+  We can do this with the following steps:
+
+```
+4.7GiB * 1024MiB/GiB = 4812.8MiB
+4812.8MiB * 1024KiB/MiB = 4928307.2KiB
+4928307.2KiB * 8Kbits/KiB = 39426457.6Kbits
+```
+
+Now we divide the kilobit size we calculated by our video length,
+to find our kilobit per second target bitrate:
+
+```
+39426457.6Kbits / 7200 seconds = 5475 Kbps
+```
+
+And here's how we could add that to our x264 command:
+
+```
+vspipe --y4m myvideo.vpy - | x264 --demuxer y4m --preset veryfast --bitrate 5475 -o x264output.mkv -
+```
+
+The `--bitrate` option, by itself,
+says that we want to do a 1-pass, average-bitrate encode.
+In other words, the encoder will still give more bits
+to sections of the video that have more detail or motion,
+but the average bitrate of the video
+will be close to what we requested.
+
+
+### Example 3: 2-Pass Encoding
+
+So far, we've only done 1-pass encodes.
+While using CRF 1-pass is great
+when you don't have a target bitrate,
+it's recommended not to use 1-pass
+for targeted-bitrate encodes,
+because the encoder can't know
+what's coming ahead of the current section of video.
+This means it can't make good decisions
+about what parts of the video need the most bitrate.
+
+How do we fix this?
+x264 supports what is known as 2-pass encoding.
+In 2-pass mode, x264 runs through the video twice,
+the first time analyzing it
+to determine where to place keyframes
+and which sections of video need the most bitrate,
+and the second time performing the actual encode.
+2-pass mode is highly recommended
+if you need to target a certain bitrate.
+
+Here's how we would run our first pass:
+
+```
+vspipe --y4m myvideo.vpy - | x264 --demuxer y4m --preset veryfast --pass 1 --bitrate 5475 -o x264output.mkv -
+```
+
+This creates a stats file in our current directory,
+which x264 will use in the second pass:
+
+```
+vspipe --y4m myvideo.vpy - | x264 --demuxer y4m --preset veryfast --pass 2 --bitrate 5475 -o x264output.mkv -
+```
+
+You'll notice all we had to change was `--pass 1` to `--pass 2`. Simple!
+
+Although x264 will automatically use faster settings for the first pass,
+it should be no surprise
+that 2-pass encoding is slower than 1-pass encoding.
+Therefore, there are still certain use cases
+where 1-pass, bitrate-targeted video
+is a good fit, such as streaming.
+
+
+## Recap
+
+We covered the basics of how to encode in x264,
+including speed presets, tunings, and three different encoding modes.
+
+Here is a summary of when to use each encoding mode:
+
+- 1-pass Constant Quality (CRF):
+  - Good for: General-purpose encoding
+  - Bad for: Streaming; obtaining a certain file size
+- 1-pass Average Bitrate:
+  - Good for: Streaming
+  - Bad for: Everything else
+- 2-pass Average Bitrate:
+  - Good for: Obtaining a certain file size
+  - Bad for: Streaming
+
+
+## Advanced Configuration
+
+Coming Soon