How to speed up DVD conversions.

With the recent acquisition of an Asus eeePC, I figured it’d be interesting to write something in regards on how to achieve reasonably fast conversions on performance-impaired computers. The information provided here applies to video conversion in general.

The Asus eeePC (900HD) has a 900Mhz Celeron processor. For conversions, Celeron processors (which have limited memory (cache) on the processor) are optimized for “Office” use, internet use, word processing and basic spreadsheets, and are not designed for processor-intensive tasks such as video conversion. While most systems that have a Celeron processor feature a speed measured in Ghz, the 900Mhz version used in the eeePC has a speed reminisent of computers of 8 years ago. While the technology used inside it’s core has significanly changed, it is not really capable of handling more demanding tasks.

So what affects conversion speed?

To be able to speed up conversions, we have to look at what conversion actually is. With video conversion, often called transcoding, we indicate the process of changing video from one format to another. DVDs come in a certain video format (MPEG2) while video files from the internet come in certain formats as well (AVI, DIVX, XVID, FLV, MPV etc) While there are devices that are capable of playback of all these different types of video content, many are not, and as of such, the various different video formats will have to be changed (converted) into a format that can play on a particular device. For most current devices (Apple’s iPod/iPhone, Sony’s PSP, Microsoft’s Zune), the format of choice is MPEG4, so DVDs (MPEG2) will need to be converted to MPEG4, DIVX needs to be converted to MPEG4, etc etc.

Besides the video format, many portable devices have certain limitations. Portable video players are designed to have an acceptable battery life (so you can watch one or two full movies on a single charge), and to achieve this, certain trade-offs have been made when thee devices were created. Many portable media players can only handle video files of a certain quality range, and only within certain screen size specifications. To make video files compatible with these players, besides converting content in the proper format, changes to the quality, as well as the screen size also have to be made.

Besides the actual conversion, things such as how the original video content is accessed, where the converted content is stored also play a major part in conversion speed.

How do we speed things up?

The main rule to keep in mind is that there is ALWAYS a trade-off. To achieve faster conversions, you WILL compromise quality.

Conversion format: Most devices accept more than just one video format. For example, all the Apple devices, iPod, iPhone, AppleTV. These can handle 2 formats of MPEG4. MPEG4 SP (Simple Profile) and MPEG4 AVC (Advanced Coding Profile, aka H264) MPEG4 AVC is used by Apple’s own iTunes video content, and offers the best possible quality (it’s the same format used for Bluray video) however, it is quite processor demanding. MPEG4-SP, the original MPEG4 format, is less processor demanding, and as a result, it is a lot faster on older systems. The iPhone (Fast) profile uses this format, and on the eeePC, this format converts at allmost 2x real-time speed (1 hour for a 2 hour movie) while the AVC format (iPhone Standard profile) converts at about 0.5x realtime, 4 hours for a 2 hour movie.

Scaling (screen size): If the video content that is converted has a bigger resolution that what the device supports, it will need to be scaled down to the lower device resolution. For DVD’s the original screen size is usually around 720×480. When this is converted to a Zune with a screen size of 320×240 for example, the video will be reduced in size to fit that screen size. To preserve as much quality as possible, during conversion additional calculations are made to scale down the video. For movies with a big screen size (bluray rip for example), that are being converted to a device with a smaller screensize (such as the Zune) it takes longer to go through the whole video picture to make it the proper size. The bigger the difference in size, the more processing power is needed to perform this task.

Picture quality: This connects to both the conversion format and the scaling mentioned above. The conversion format selected determines the way the video quality is adjusted. Some formats compare each video picture, and just store the differences with a certain (key-)frame, while other formats perform certain calculations to achieve the format conversion. Each format works differently, and the wy this works is too complicated for this particular article, and will be covered in another topic. The video quality setting (kbps) determines how much “data” can be used for the video during a certain time. This determines the resulting filesize, as well as how the picture looks. The higher the quality, the better the video will look when completed, however, higher quality also means that there will be more time spend during conversion to achieve the quality.

Drive speed: While not as important on slower computers, the drive speed does affect conversion speed. The conversion can only work as fast as it has information to work with, so if you are converting a DVD, and the drive is too slow, the conversion will be waiting for the DVD drive to deliver the information it needs to convert. In a similar manner, the drive where the created files are stored. When the conversion has converted a piece of the movie, it needs to store this, and if the location where the files are saved is too slow, the conversion is paused untill the data is saved to the drive.

A few tips for drives:

* Never set the output folder to a flash-drive/pendrive/SD/CF card. These drives do not have a consistent data rate, and you will experience severe slowdowns during conversion.Convertto your computers harddisk first, and when done, copy the files over to the drive. This is a lot faster.

* Never convert directly to the memory of your device. Most devices (PalmOS, Windows Mobile)use some form of sync-software to establish a connection to your device, and when you convert directly to your device, this sync-software will continiously be “assisting” in the data transfer. This will slow down conversions severely. Convert the files to your compute’s harddisk first, then transfer the completed files over.

* Never convert from an external drive to the same external drive.If you are using an external harddisk for your video files, converting to and from the same drive will result in “traffic” jams during conversion. Data is being read from, and send to the harddisk at the same time, causing the conversion to be quite slow.  Convert the files from your external harddisk, and save them to your computer first. When the conversion is finished, move them to your drive.

The above screenshot of DVD Catalyst 3 shows a conversion of “Navy Seals” (first 10 minutes of the movie only) with 4 different conversion settings. Conversions were done on an Asus eeePC 900HD (900Mhz Celeron), with an external USB2 Lite-On DVDdrive to the internal harddisk of the system.

iPhone (Standard) Profile : 480×320 resolution, AVC (h264) video format (500Kbps) 0.77x realtime (2 1/2 hours for a 2 hour movie)

iPhone (Fast) Profile : 480×320 resolution, MPEG4 SP video format (500Kbps) 1.83x realtime ( 1 1/4 hours for a 2 hour movie)

iPhone (HQ) Profile 720×320 resolution, AVC (h264) video format (700Kbps) 0.68x realtime (3 hours for a 2 hour movie)

iPhone (Small) Profile 288×192 resolution, AVC (h264) video format (180Kbps) 1.73x realtime (1 1/2 hours for a 2 hour movie)