Encoding Videos Using x264 and Virtual Dub

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Encoding videos using x264 and VirtualDubEncoding videos using x264 and VirtualDubEncoding videos using x264 and VirtualDubEncoding videos using x264 and VirtualDub

February 21, 2006

December 29, 2006: You can temporarily get an older version of x264 for this guide over here:

http://videos.co23.com/x264-440-install.exe.

October 10, 2006: A lot of people at doom9 are no longer provided any kind of support or answers regarding

x264 and VFW (VirtualDub). As such, you can no longer get a "latest build" of x264 VFW which this guide requires.

If I can find some time, I'll provide another guide which utilizes the Command Line Interface x264, MeGUI,

AviSynth, mkv container, and optionally avc2avi. It's harder to explain but once you get it down it makes it much

easier to achieve consistent results.

A lot of people often ask me, "what codec did you use to encode that video?" I usually reply to them with "x264"

and their immediate response is "where can I get that?" If you have never heard of x264 and H.264 or Advanced

Video Coding (AVC), they are the next generation video codec and standard respectively. x264 is a very impressive

codec and can achieve high video quality at low bitrates.

In this guide, I will show you one method to compress video with x264. All of the tools in this guide are free,

open source, and run on Windows. The initial setup time is a little slow and the encoding process is slow as

well, but the quality to file-size ratio is impressive. This guide is not about how to create your own videos,

only how to compress existing computer video (AVI files and the like) to a high quality format.

x264 is still in development, but recent builds have shown that it is already powerful and usable. Unfortunately,

your viewers will need x264 decoder software to play videos. Another drawback is that x264 is much more

processor intensive; much older computers with 1ghz cpus or slower may have trouble decoding x264 videos. Some

less knowledgeable users will be a little frustrated at first, but if they have the hardware and the correct software,

they are typically fairly impressed with the results. If you would like to learn more about x264 visit the videolan

developer website.

The method described in this guide uses the fewest number of tools. On the other hand, it is slower and more

prone to errors and crashes during encoding or batch encoding. The crashes occur because the x264 codec is still in

development and it appears the "Video For Windows" (VFW) style codec has more bugs. VFW and the AVI container

format also have known issues surrounding H.264 and other newer codecs. A VFW codec is the type of codec

VirtualDub uses and is built into Windows. AVI is a container format that is also supported by Windows.

Unfortuntely, both are old and both have flaws that are not intended to be compatible with H.264. With a number

of hacks, however, the AVI container can be used. Fortunately, you do not have to worry about the incompatibilities

for this guide, but it is good to know that they exist. If you want to know the details, visit this doom9 forum thread.

This guide is intended to be a starting point especially for people very new to video encoding. In later guides I will

show other tools that will actually get the job done better than the toolset described in this guide.

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Required ToolsRequired ToolsRequired ToolsRequired Tools

VirtualDub [VirtualDub homepage]

Open-source video processing tool.

Sharktooth's x264 Standard or Lite Package [doom9 forums]

The open-source H.264 codec.

ffdshow daily build [Sourceforge]

An open-source codec pack for playing x264 encoded files.

(Optional) LameMP3 ACM codec [rarewares.org]

Open-source MP3 audio codec. Necessary for adding compressed MP3 audio to the video.

Installing VirtualDubInstalling VirtualDubInstalling VirtualDubInstalling VirtualDub

Get a stable release build of Virtualdub at http://virtualdub.sourceforge.net/. There version of Virtualdub

used in this guide is 1.6.10. Other versions of the program close to this version should work as well.

VirtualDub is not packaged with an installer so you will choose where you want the program to reside. Installation

is straight-forward once you understand what's going on:

Extract the contents of the downloaded ZIP file to a location on your computer.1.

Once complete, you can go to the location where you extracted the files and run VirtualDub.exe to start

the software.

2.

(Optional) For convenience, you may want to create a shortcut to VirtualDub.exe on your desktop or start

menu.

3.

Installing x264Installing x264Installing x264Installing x264

Get one of Sharktooth's x264 daily builds at the doom9 MPEG-4 AVC forum daily builds thread. You are

interested in either the Lite or Standard package. Choose the Standard package if you are unsure.

The x264 package comes with an installer that will guide you through the installation process. The default settings

should work.

Installing ffdshowInstalling ffdshowInstalling ffdshowInstalling ffdshow

Get ffdshow from the ffdshow daily builds webpage.

ffdshow comes with an installer as well to guide you through installation. While the defaults will work, I highly

recommend un-checking the Postprocessing video filter and volume normalization audio feature during installation.

Installing LAME MP3 ACM CodecInstalling LAME MP3 ACM CodecInstalling LAME MP3 ACM CodecInstalling LAME MP3 ACM Codec

Lame MP3 is necessary to add compressed audio to your video. Get the Lame MP3 encoder Bundle from

rarewares.org. To be safe, you probably want to use a beta instead of an alpha.

Extract the files in the ZIP file to a temporary folder on your desktop. Open the folder and right click the

LameACM.inf file and click "Install." A dialog may warn you about installing the software, to continue click "continue


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anyway." You might be prompted to restart before the changes will take effect. Once installed, you can delete the

folder on your desktop.

Encoding Passes, Bitrate, and Reference FramesEncoding Passes, Bitrate, and Reference FramesEncoding Passes, Bitrate, and Reference FramesEncoding Passes, Bitrate, and Reference Frames

Before you begin encoding, you need to educate yourself a little about some common encoding jargon and

methods: encoding passes, bitrate, and reference frames.

Video codecs utilize data they get from prior encoding passes to help determine how to distribute the bits over the

entire video. Bits are the data used to describe the video and bitrate determines how many bits are available for a

period of time. For each pass, the codec will analyze the video as a whole and determine which parts are more

complex than others. On following passes, the codec distributes bits over the entire video utilizing what it saw on

previous passes. For example, if you have less complex scenes with still-shots or very little motion, the codec will

detect that on the first pass. On the second pass it will know that it can take away some data from that scene and

place it on a more complex scene with lots of motion or lots of detail. With single pass the codec does not know

what to expect 1 minute later in the video, so it will guess on how to distribute data over small chunks of the video

it sees at that point in time. With multiple passes, the first pass is generally thrown away and done very quickly

since the codec has no data to work with. Second and third passes are done applying the codec's full capabilities

and produce the final encoded video. x264 is capable of performing three or more passes, however, after the

second pass the benefits start to diminish quickly. If you are really picky, you can see the small differences between

two and three pass encodes. Many experienced encoders will generally say a fourth pass does not provide any

noticeable improvements, but the possibility of doing them is always there.

The bitrate determines how big the final file will be and how much the quality will suffer; the larger the bitrate,

typically the better the video will look. Likewise, as you lower the bitrate, the quality decreases. I recommend

experimenting with a short 30 second clip and do a little bit of math to determine how big your actual video will get

and what bitrate you want. As a reference, if your video file has a resolution of 640x480 and frame rate of around

30 frames per a second then a bitrate of 1000 provide pretty good quality depending on the video contents. There

is no way to tell how good the quality will be until you actually try it. That is why it is a good idea to experiment on

a short clip first before wasting hours of encoding the entire video. For things like cartoon animations you can get

away with fairly low bitrate before the video starts to show noticeable defects. For things like detailed video game

clips or high action scenes, a high bitrate will be necessary. Finally, choose a clip that contains varying amounts of

motion or detail, otherwise you may get a false impression of the bitrate you need.

Another piece of useful information is that many encoders typically encode movie content so they can store the

movie on cheaper media. These users will often try to hit a target file size rather than a target bitrate. For

example, if they have a 700mb capacity cd, they often will use a bitrate calculator to determine what bitrate they

can use to make the file size exactly 700mb. When getting started, I would not worry too much about hitting

specific sizes. Most people reading this probably will want to use this information to compress content that is

distributed over the internet rather than for archive purposes.

The default VFW x264 codec uses a Max Reference Frames value of 1. In this guide, we change this value to 5 in

order to increase the final video quality. Generally, the higher the number of reference frames increases the quality

of the video. Obviously there is a cost to increasing the reference frames: much longer encoding time. If you want

to try playing with this setting, I would go no higher than 15 reference frames. There are many more settings in

x264 and a lot of them are not accessible from the VFW codec. Most of the other default settings are already pretty

good so you do not have to worry about them for now.


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Encoding the VideoEncoding the VideoEncoding the VideoEncoding the Video

Now that you have all the tools installed, you can start playing with the encoding process. For this method, I will go

over two encode methods: single-pass and two-pass. The fastest way to get a result is to use single-pass, but the

quality will definitely be worse than the results of a two-pass encode. Two-pass is the best way to improve the

quality without tweaking with the codec settings. Single-pass is good if you are short on time, do not care about the

resulting file size, and do not mind the quality. Often none of those are true, but it is still useful to know single pass

first before two-pass. I recommend using single pass with a high bitrate to temporarily store uncompressed video.

Single PassSingle PassSingle PassSingle Pass

Start VirtualDub and open your video file by dragging the AVI to VirtualDub. You should be able to play the video

within Virtualdub by hitting the play button with a small "I" at the bottom left.

Now we need to configure the video encoder settings:

Go to the Video menu and make sure Fast Recompress is selected.1.

Go back to the Video menu and click Compression.2.

In the list, click x264 - H264/AVC encoder.3.


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Now click the configure button.4.

x264 codec window should show, make sure the drop-down has Single Pass - Bitrate.5.

Now select your average bitrate value.6.

To boost the quality, we will change the reference frames value:

Click on the MBs&Frames Tab7.

For Max Ref. Frames enter a value of 58.


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Click ok, and ok again.9.

Video encoding settings are now ready.10.

If you have audio along with your video, you will want to compress that as well, if not, you can skip the following

steps.

Click the Audio menu, and make sure Full Processing Mode and Source Audio are selected.1.

In the Audio menu, click Compression.2.

Select Lame MP3 in the list3.


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Select your desired audio bitrate on the right (recommended: 44100 Hz, 128 kbps CBR, Stereo).4.

Click ok.5.

Audio encoding settings are now ready.6.

Now you are ready to begin encoding. Click File then Save as AVI.... Enter the name of the avi encoded file and

click Save.

A VirtualDub progress screen should show up.


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Two PassTwo PassTwo PassTwo Pass

For two pass, we start out just like single pass: Start VirtualDub and open your video file by dragging the AVI to

VirtualDub. I will not repeat duplicate screenshots here so refer to Single Pass if you get confused.

Before we continue, you will be setting a lot of things and sending them to VirtualDub's Job Control. Job Control

(hotkey F4) is basically a list of things VirtualDub will do in sequence. At anytime, you can remove the jobs and

reconfigure them before you do the actual encode in the Job Control window. This is nice to know if you accidently

add a job that you did not want.

Configuring the 1st PassConfiguring the 1st PassConfiguring the 1st PassConfiguring the 1st Pass

These steps are very similar to steps described in 1pass encoding except we change the pass setting in the x264

codec screen and we queue the jobs to job control in the Save as dialog.

Configure the video encoder settings for the first pass:

Go to the Video menu and make sure Fast Recompress is selected.1.

Go back to the Video menu and click Compression.2.



x264 codec window should show, make sure the drop-down has Multipass - First Pass (fast).5.

Now select your average bitrate value.6.

Click on the MBs&Frames Tab7.

For Max Ref. Frames enter a value of 58.


First Pass video encoding settings are now ready.10.

Since this is the first pass, we don't need to do anything with the audio, so we will disable it:


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Click the Audio menu, and select "No Audio."1.

Now we tell VirtualDub to queue the first pass:

Go to File, and click Save As Avi...1.

In the dialog, check Don't run this job now; add it to job control... at the bottom.2.

Enter a file name.

The file name you enter here is not the final video file name; it is just a temporary file for encoding. Enter

something like video_first_pass.avi so you know to delete the file after the pass completes.

3.

Click save4.

The dialog should disappear and the first pass should be queued in VirtualDub's job control.5.

Configuring the 2nd PassConfiguring the 2nd PassConfiguring the 2nd PassConfiguring the 2nd Pass

For the second pass we just need to set the codec to the 2nd pass and add our audio compression settings if we


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have audio.

Configure the video settings for the second pass:

Go to the Video menu and click Compression.1.



x264 codec window should show, change the drop-down to Multipass - Nth Pass.

The bitrate you selected in the first pass should still be the same so you do not need to change anything

else.

4.


Second Pass video encoding settings are now ready.6.

If you have audio along with your video, you will want to compress that as well:

Click the Audio menu, and make sure Full Processing Mode and Source Audio are selected.1.

In the Audio menu, click Compression.2.

Select Lame MP3 in the list3.

Select your desired audio bitrate on the right (recommended: 44100 Hz, 128 kbps CBR, Stereo).4.

Click ok.5.

Audio encoding settings are now ready.6.

Now we queue the second pass:

Go to File, and click Save As Avi...1.

In the dialog, make sure to check Don't run this job now; add it to job control... again.2.


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Enter a file name.

The file name you enter here is the final video file.

3.

Click save4.

The dialog should disappear and the first pass should be queued in VirtualDub's job control.5.

Starting the Queued JobsStarting the Queued JobsStarting the Queued JobsStarting the Queued Jobs

Now we can tell VirtualDub to start the jobs we queued:

Go to File, and click Job Control...1.

The Job Control window opens, make sure your two entries from earlier are listed. The job names are

automatically assigned by VirtualDub so do not worry if they are not to your liking.

2.

Click the first job3.

Now click the start button4.

VirtualDub should now be working and will automatically start the second pass after the first pass completes. Once

both jobs complete, your video will be ready.

Conclusion: Play Your x264 Encoded VideoConclusion: Play Your x264 Encoded VideoConclusion: Play Your x264 Encoded VideoConclusion: Play Your x264 Encoded Video


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x264 Video Playing (actual result not shown; image is highly compressed)

When

the

encoding

process

finishes,

you can

play the

AVI file

you

saved

and

delete

the stats

files.

This is

where

ffdshow

will be

used.

Double-click the file and your media player should start playing the video. While the video is playing, a small

ffdshow icon should appear in your system tray next to your clock. Right-clicking the ffdshow icon will give you

some options. If you forgot to turn off postprocessing during the install, you can turn it off here while the video is

playing.

Hopefully you took my advice and worked with a short 30 second clip. Depending on your bitrate, the resulting

video will turn out worse than you would like or perhaps it turned out better but the file size is still a little big. With

some quick math you can determine how big a full length file would be. I would keep playing with the bitrate until

you hit the point where you are satisfied with the quality to file-size ratio.

The encoding process is generally slow. The biggest external factors affecting encoding speed are: CPU speed,

video resolution, and video length. Encoding speed also depends on the codec settings. The number of settings in

x264 constitutes writing a another guide so I will not cover them here. A good place to look for more information is

the doom9 AVC forums. In a following guide, I will show you how to utilize a tool called MeGUI to make the

encoding process a little simpler and help you get much better results without becoming an x264 expert.

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© 2006 Rhomel Chinsio


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Encoding Videos Using x264 and Virtual Dub

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