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Why Is My Video Striped? Scanning Systems and Preview Problems.

When we spoke about HD video, we explained what shorthands for HD videos like 1080p, 1080i and 720p mean.
The letters p and i are used to designate the scanning system: progressive scanning (p) or interlaced scanning (i).
We promised to discuss the scanning systems and related problems later.
So, let’s start.

Scanning systems

A scanning system type characterizes the way the image is being redrawn when refreshing picture.
There are two different scanning systems – progressive scanning and interlaced scanning.

Progressive scanning redraws an image frame (all of its lines) when refreshing each picture.

Interlaced scanning system implies that each frame is divided into two half-frames (or fields). One field contains all the odd lines of the image, the other contains all the even lines of the image. Thus, during the first image refresh operation the system draws odd numbered lines, and then draws the remaining even numbered lines during the second refreshing.
This technique allows to double a frame rate of a video signal without consuming extra bandwidth. Interlaced scanning was initially designed for TV broadcasting so that the refresh rate of a screen fits the power frequency.

Watching an interlaced video on a device that uses progressive scanning method causes a very unpleasant effect.

What is the combing effect? Why does it occur?

Interlace (or combing) effect occurs when an interlaced video is being played on a device that employs progressive scanning. Edges of moving objects have the form of a “comb”, the video is covered by horizontal stripes that distort the image (see Pic. 1).

The cause of this effect is that a progressive scanning combines two adjacent half-frames to draw the image. Lines of these two half-frames interleave, that is the first line from the first half-frame is drawn, then the second line from the second half-frame, the third line from the first half-frame, the fourth line from the second half-frame, and so on. The combined half-frames can contain different motion phases, so that the lines are shifted relative to each other, and the picture looks striped.

Where and when can I see the combing effect?

If you watch TV on your computer using a TV tuner, you have probably seen this effect (as computer monitors use progressive scanning system, while TV broadcasting standards imply interlaced scanning).
Many camcorders also shoot interlaced video, so you will see interlace stripes when watching it on your computer.
At last, you can face this problem when ripping DVD, since many DVDs are interlaced too.
You should remember that the combing artifacts are most visible on moving images.

How to get rid of combing artifacts?

To be played correctly by devices that use progressive scanning, an interlaced video is converted into a non-interlaced form. This process is called deinterlacing. The conversion can be performed both hardwarily (by devices, such as TV sets, DVD players and computer video cards) and softwarily (by the means of video conversion software).
For example, Need4 Video Converter allows applying deinterlacing to MPEG video files. Pic.1 gives an instance of software deinterlacing performed by Need4 Video Converter program.

February 24th, 2011
Posted in Informative | No Comments »

HD in Q&A

Q: What is HD video?
A: High-definition (HD) video implies video that has higher resolution than standard-definition (SD) video, i.e. higher than 720×576.

Q: What is the difference between HD and SD videos?
A: Evidently, the main difference is the higher resolution. Moreover, HD and SD videos can be easily distinguished visually – HD video is notable for much higher detail level than standard video.
Pic. 1 illustrates the difference.

Q: What resolutions HD videos have?
A: The most widely used resolutions are 1920×1080 and 1280×720 pixels.
In Pic. 2 you can see the comparison of the most popular video resolutions, both HD and SD.

Q: What do shorthand names like 1080p, 1080i and 720p mean?
A: Numbers (1080 and 720) stand for a vertical frame resolution of 1080 or 720 lines, respectively.
The letters p and i are used to designate the scanning system: progressive scanning (p) or interlaced scanning (i).
We’ll keep different scanning systems and related problems to be a topic of a next post as it is a good question with a lot to say about. We’ll surely discuss the matters later.
Thus, 1080p stands for 1920×1080 progressive video, 1080i – 1920×1080 interlaced video, 720p – 1280×720 progressive video.

Q: What is Full HD?
A: Full HD is a marketing name for 1080p and 1080i video.

Q: What are the most popular HD formats?
A: Today the most popular HD video container format is MPEG-2 Transport Stream, the most often used codecs are H.264 (AVCHD) and MPEG-2.

Q: Do I need a special device to watch HD video?
A: To be able to watch HD video you need a device (computer monitor, television display, projector, etc.) that can process and display high-definition source video signal. This capability is generally determined by technical characteristics of a display, such as display resolution.

Q: If I convert a standard-definition video to a high resolution, will the output video be an HD video?
A: Nominally, such video can be called HD video, as the main difference between HD and standard video is higher resolution. But if you convert video from a lower resolution to a higher one, the quality of the video will not be improved. There are devices that can upscale video (i.e. convert video from a low resolution to a higher one), but the quality of upscaled videos is still lower that the quality of “true” HD videos.

Q: Comparing the output quality of a video file upgraded to HD with the help of video converting software and an upscaling device, which quality is better?
A: The most conversion programs use simple bilinear upscaling algorithm, while devices use more complex methods allowing to improve picture quality, so that the quality of hardwarily upscaled videos is better that the quality of softwarily converted ones.
However, as we have already said, the quality of upscaled video is worse compared to “true” HD.

Q: How can I tell upscaled video from “true” HD video? Are there any objective characteristics?
A: Unfortunately, there are no objective characteristics that an ordinary viewer can use to differentiate “true” HD video from upscaled video. It can be done visually by comparing video frames: HD video frame will have much more small details than an upscaled video frame (see Pic.1). One can say that HD video contains more information per a square unit.

February 8th, 2011
Posted in Informative | 3 Comments »

The End of the Trilogy: How to Solve Aspect Ratio Problems

The most common problems

Previously we have mentioned the most common problems connected with aspect ratio: when you play video on your DVD player it is stretched horizontally or vertically. Such problems can be easily solved hardwarily – by setting a DVD player or a TV set to the correct aspect ratio.

But what can you do if your video is shown incorrectly when being played in a software media player? For example, you have a video file that was converted before and for some reason it was converted with the wrong aspect ratio.

There is one more problem related to aspect ratio. Our users often ask how to remove black bars at the edges of the video.

With Need4 Video Converter you will easily convert your stretched video so that it becomes normal as well as remove unwanted black bars.

Classification of the problems

Let’s systematize all the problems associated with aspect ratio we have mentioned above:

1. The video has incorrect aspect ratio and is stretched
   1. vertically (all objects look narrow and prolonged);
   2. horizontally (all objects look flattened out).
2. The video has correct aspect ratio and is not stretched, but has black bars
   1. on the top and bottom;
   2. on the left and right.

Solution methods

1. Correcting stretched video.
   1. Most probably, a widescreen (16:9) video was stretched to the 4:3 aspect ratio, so that the original aspect ratio was broken. To correct this, we should stretch the video horizontally leaving the height of the video unchanged (see Pic. 1).
      
      Pic. 1: Stretching incorrectly converted video back to 16:9

      Knowing the height of the converted video, we need to calculate its width. Let’s denote the width of the video by W, and the height of the video by H.
      As the converted video is supposed to be 16:9, i.e. W:H = 16:9, the width can be calculated as follows:
      W=16×H:9.

   2. It looks like a 4:3 video was stretched to the 16:9 aspect ratio, so that the original aspect ratio was broken. To correct this, we should compress the video horizontally leaving the height of the video unchanged (see Pic. 2).
      
      Pic. 2: Stretching incorrectly converted video back to 4:3

      The converted video is supposed to be 4:3, i.e. W:H = 4:3, then the width can be calculated as follows:
      W=4×H:3.

2. Removing black bars.
   1. Most likely, a widescreen video (16:9) was converted to 4:3 using the Letter Box resize method. More information about resize methods here.
      The picture looks fine (not stretched), but black bars are added on the top and bottom of the video. This situation can be very unpleasant when you watch this video on your widescreen TV set, as it adds its own bars to the sides of the video to inscribe it to the screen. This is called windowboxing or postage stamp effect. Your video will look as in Pic. 3.
      
      Pic. 3: Windowboxing (postage stamp effect)

      You can remove the bars and return the video to the 16:9 aspect ratio using the Crop resize method. We need to crop the video vertically leaving the width of the video unchanged (see Pic. 4).
      

      Pic. 4: Cropping letterboxed video back to 16:9

      Since the converted video is supposed to be 16:9, i.e. W:H = 16:9, the height can be calculated as follows:
      H=9×W:16.

   2. It appears that a 4:3 video was converted to 16:9 using the Letter Box resize method. In this case black bars are added on the left and right of the video. You can remove them and return the video to the 4:3 aspect ratio using the Crop resize method.
      We need to crop the video horizontally leaving the height of the video unchanged (see Pic. 5).
      
      Pic. 5: Cropping letterboxed video back to 4:3

      The converted video is supposed to be 4:3, i.e. W:H = 4:3, so that the width can be calculated as follows:
      W=4×H:3.

Conversion instructions

To perform conversion of a problematic video file, follow these steps:

• add your video to Need4 Video Converter and select the necessary preset from the Output format drop-down list;
• click Settings under the Output format list;
• uncheck the Video same as input and Keep aspect ratio checkboxes;
• click the Options button in the Video stream area, select the target aspect ratio and click OK;
• specify the width and the height of the converted video that were calculated above;
• select from the Resize method list
  1. Stretch if you want to correct stretched video;
  2. Crop if you want to remove black bars from the edges of your video;
• click OK;
• convert your video.

If you still have problems or need detailed instructions on converting a certain video file, please contact our Support Team.

January 31st, 2011
Posted in Informative | 1 Comment »

Aspect Ratio: from Theory to Practice

In our previous post we considered what aspect ratio of a video file is, what aspect ratios are most widely used and what problems are connected with aspect ratio. In this post we will try to give clear instructions on converting video with a glance of aspect ratio using Need4 Video Converter.

There are several alternatives possible:

1. You want to keep the aspect ratio of the original video unchanged.
2. You want to change the aspect ratio of the video you have:
   1. convert 16:9 video to 4:3;
   2. convert 4:3 video to 16:9.

Let us review all these cases.

1. To make sure that converted video will have the same aspect ratio as the original video, you should:
   • add it to Need4 Video Converter;
   • right-click on the file and select Information; in the window opened you will find information about your video file, including its aspect ratio;
   • select the necessary preset from the Output format drop-down list;
   • click Settings under the Output format list.
     If the Video same as input checkbox is checked, converted video will have the same resolution and aspect ratio as the original video.
     If the Video same as input checkbox is unchecked by default or you need to uncheck it (for example, when you want to resize your video), make sure that the Keep aspect ratio checkbox is checked.
     For the presets of the DVD Quality Video group you can select the necessary aspect ratio from the corresponding list;
   • click OK;
   • convert your video.
2. Aspect ratio of your video can be changed as follows:
   • add your video to Need4 Video Converter and select the necessary output format;
   • click Settings under the Output format list; uncheck the Video same as input and Keep aspect ratio checkboxes; specify the width and height for converted video;
   • click the Options button in the Video stream area and select from the Aspect ratio list:
     1. 4:3, if you want to convert 16:9 video to 4:3;
     2. or 16:9, if you want to convert 4:3 video to 16:9;
   • click OK;
   • select the necessary resize method from the Resize method list. For more information about resize methods, please check this article;
   • click OK;
   • convert your video.

If you still have problems with aspect ratio, feel free to contact Need4Video Support Team.

November 11th, 2010
Posted in Informative | 2 Comments »

Simply about Aspect Ratio

What is aspect ratio

According to Wikipedia, aspect ratio of an image is the ratio of the width of the image to its height, expressed as two numbers separated by a colon, e.g. x:y (pronounced “x-to-y”) .

The most widely used aspect ratios

The most common video aspect ratios are 4:3 and 16:9.

• The 4:3 ratio for standard television has been in use since television’s origins and many computer monitors employ the same aspect ratio.
• 16:9 is the international standard format of HDTV, non-HD digital television and analog widescreen television.

These aspect ratios can be easily distinguished. 4:3 has more “square” form, while 16:9 is more “rectangular” (See Pic. 1).

It should be mentioned that 16:9 aspect ratio is considered to be more aesthetically pleasing and closer to human eyesight. This aspect ratio approximates to the so-called golden ratio.

Most common problems connected with aspect ratio

1. All objects look narrow and prolonged, faces are “long”. This can happen, for example, when you watch a widescreen video (16:9 aspect ratio) on a square TV set that has 4:3 aspect ratio, so that your video is stretched vertically to fit the screen of the TV set (see Pic. 2).
   
   Pic. 2: Video stretched to 4:3 compared to the original video (16:9)
2. All objects look flattened out. This can happen if you watch an old movie or TV show that was shot in 4:3 aspect ratio on a widescreen TV set, so that your video is stretched horizontally (see Pic. 3).
   
   Pic. 3: Video stretched to 16:9 compared to the original video (4:3)

How to solve aspect ratio problems

Many problems connected with aspect ratio can be solved hardwarily – by setting a DVD player or a TV set to the necessary aspect ratio.
If you want to convert your video, you should remember about aspect ratio. Here you can find some tips on converting video with a glance of aspect ratio.

Why aspect ratio and frame size shouldn’t be mistaken

Probably, you know that a pixel is the smallest unit of an image. In video files square pixels are primarily used. It is evident that the width and height of a square pixel are equal to each other. In this case, the ratio between video dimensions in pixels will correspond to the aspect ratio of the video file. For example, a video file which consists of square pixels has 640*480 resolution, and its aspect ratio is 4:3 (640:480 = 4:3).

However, DVD files often use non-square pixels (they have rectangular shape, and the pixel width slightly differs from its height). In this case, the ratio between video dimensions in pixels will differ from the aspect ratio of the video file. For example, a 4:3 DVD video can have 720*480 resolution (720:480 ≠ 4:3). This difference is conditioned by different dimensions of a non-square pixel.

November 11th, 2010
Posted in Informative | 2 Comments »

Cats & Dogs or a Few Words About Resize

Sometimes you may need to resize your video or change its aspect ratio. For example, you have a widescreen (16:9 aspect ratio) HD video that you want to watch on your iPod (4:3 aspect ratio). If you try to upload the video to your device without resizing, it will not be played on your device or will be played incorrectly (probably, you have seen “long faces”).

You can resize your video with Need4 Video Converter. The program offers you to select such options as resize method and resize quality. They can be found as follows:
- open Need4 Video Converter and add your video file to the program file list;
- select the output format for conversion;
- click Settings under the Output format drop-down list;
- in the format settings window opened you can specify resize method and quality.

First, let us review resize methods: Stretch, Letter Box and Crop (see Pic. 1).

• Stretch – the original video frame is stretched (or condensed) to the specified frame size (width and height).
• Letter Box – the original video frame is inscribed into the output frame. The aspect ratio stays the same, and free space between the input and the output frames is filled with black bars.
• Crop – the original video frame is inscribed into the output frame. The aspect ratio stays the same, and the parts of the input frame that transcend the output frame size are cut off.

As you can see from the description, when using the first method the aspect ratio of the original file is changed, while the other two keep the aspect ratio unchanged but by different ways.

As regards resize quality, there are two options available: Normal (Fast) and Best (Slow). Pic. 2 displays differences between these two modes.

• Normal (Fast) – this mode works faster than the second one (as it is evident from their names), but the quality of the output video is lower. When reducing the frame size (if the input frame is larger than the output frame), thin lines may look broken and have irregular thickness. When increasing the frame size (input video frame is smaller than the output video frame), there may be visible pixelization effect.
• Best (Slow) – this mode works much slower than the first one, but the quality of the output video is better. When reducing the frame size – thin lines are not distorted, when increasing – the picture is smoothed.
  

  October 7th, 2010
  Posted in Informative | 4 Comments »

Why Codec Pack?

When we need codecs

Even if you are an advanced computer user, you have probably experienced problems when playing video/audio files. Here is the list of the prevailing problems:

• video plays without sound;
• sound plays but there is no video;
• a media player doesn’t play a file at all giving an error message.

The same problems can appear when converting files: the result of conversion plays incorrectly.

We often recommend our users who face such problems to download and install codecs.
You may ask: “Why do I need additional software? How to get to know which codec I need?”

What is a codec

According to Wikipedia, codec (from English COder/DECoder) is a computer program capable of encoding and/or decoding data stream or signal.
You should remember that a codec doesn’t playback video and audio files, it just helps other programs (media players, converting software) to open, playback and convert video and audio files correctly.

Also, you should differ video format and video codec. Sometimes they are mistaken because a format and a codec can have the same name. A file format can be considered as a type of container. Inside the container is data that has been compressed by using a particular codec (or a number of codecs). For example, a file in the AVI (Audio-Video Interleaved) format can be compressed by several codecs, including MPEG4, DivX, Xvid, MP3, and others. You can find more information about codecs on the Microsoft website.

What codecs to install

So, how to find out which codec is needed to convert a certain file?
We usually recommend our users to install K-Lite Codec Pack, QuickTime Player and DivX Plus Codec Pack.

• K-Lite Codec Pack is a free package of codecs that are needed for encoding and decoding various video and audio formats. More information here.
  You may need to download and install this codec pack if you have a file in the FLV, MKV, MP4, RM format or other.
  When installing K-Lite Codec Pack, you can optionally install Media Player Classic (MPC), a free easy-to-use multimedia player.
• QuickTime Player is a free multimedia player for both Mac OS X and Windows operating systems. If you want to play or convert a MOV file, you should have the player installed.
• DivX is a proprietary codec developed by DivX, Inc. The codec has become popular due to its high efficiency. It is used to strongly compress video with minimal quality loss.

In conclusion, please note: if you are not sure which codec you need to open and/or convert your file, you can always contact Need4Video Support Team.

September 15th, 2010
Posted in Informative | 1 Comment »