MPEG-1 and MPEG-2 Preset Customization

Last Updated: Apr 25, 2014 01:20PM PDT
There are many default MPEG-2 prests in Squeeze to help you make DVD files and discs, blu-ray files. If you have need of an MPEG-1 or 2 preset for more general purpose, this article will help you understand the preset settings to achieve optimal results.

Please note that most of the default Mpeg-2 presets that come with Squeeze are created to perform specific functions. Most of the default presets have very specific constraints and the modification of the settings may invalidate the output file’s intended purpose. For example, the DVD presets have format constraints that comply with DVD player standards. If you change these settings you may get errors in the preset creation, as well as an output file that is unsuitable for its intended format. The same applies to Blu-Ray presets. Other Mpeg 2 presets such as Transport Stream and HDV presets have more flexibility, but it is advised that you refer to the specifications for your particular project before making modifications besides data rate and aspect ratio.

There are default presets that come standard without any format constraints. The presets are labeled HD/frame size/field encoding/frame rate (i.e. HD720p50, HD1080i60)



For the purpose of this walk through the HD720p30 preset will be used. The reason is arbitrary, seeing as the user will want to use the preset that most closely resembles the desired output and then make modifications from that point.


General Settings
These settings affect the overall file, both audio and video.
Name
The name of the preset. To create a new preset, enter a name that you will recognize.
Total Data Rate
Reflects the total Data Rate of the combined audio and video Data Rates. This field is display only. It changes as the video and audio options change.
Format Constraints
Allows you to select from a list of available format constraints. If you know the format you want to constrain your file to, (i.e. DVD, Blu Ray, ATSC) then you can select a preset. if this output file is for general purpose such as archiving, you should leave this field left as NONE.
Stream Type
The Stream Type field is only available for QuickTime, MPEG-4, and MPEG (MPEG-1, MPEG-2, VCD, SVCD, and DVD) compression.
Elementary Stream will create separate Audio/Video tracks which is necessary for DVD/Blu-Ray file creation.
Program Stream will output a single file containing Audio and Video information. This is the ideal stream type for general use.
Transport Stream is for specific purposes such as ATSC and Adaptive Streaming files.

Simple Video Settings
First we will cover the simple settings on the video tab before expanding the settings options and explaining the advanced settings.
Video Check-box
Includes video in the preset. If this is unselected, the video options cannot be changed, and the preset will export audio only, according to the audio settings.

Codec
A video codec is the software application that compresses the video portion of your movie. Sorenson Spark Pro and On2 VP6 Pro are the video codec options for Adobe Flash (.flv). As mentioned above, On2 VP6 is recommended for all desktop use.

Format
This allows you to choose NTSC or PAL if you have need to constrain your settings to those formats.

Method
Allows you to select from the available compression methods. Your options are 1Pass VBR, 2-Pass VBR, or 1- Pass CBR.
Variable bit rate (VBR) method varies the amount of output data per time segment. VBR allows a higher bit rate to the more complex segments of media files while a lower data rate is allocated to less complex segments (i.e. talking-heads or Power Point presentations). This keeps the quality consistent while keeping file size low.
With VBR, you have the option of 1 pass, or 2 pass. Multiple passes will provide superior output quality, but will also multiply the amount of time it takes to complete the encoding job.

Constant bit rate (CBR) keeps a consistent bit rate throughout the duration of the file. This can be helpful when using a streaming server that needs a constant bit rate stream. Because the bit rate is consistent regardless of complexity of video content CBR encoded files usually need a higher data rate and produce larger file sizes than files using the VBR method.
Frame Rate: Frames/Sec.
Indicates the number of frames (individual pictures of the movie) that are played each second. The higher you set the Frame Rate, the smoother the playback appears. The default frame rate is 1:1, which means if the source file is 30fps (frames per second), the output will be 30fps as well. This is the optimal setting unless your source file is greater than 30fps, in which case you will want to specify the Frame Rate.

Data Rates
Data Rate (bit rate) is the single greatest determining factor of the quality and size of the output video file. Select the Preset Data Rate that meets the needs of your audience. The greater the data rate, the higher quality the output, but larger the resources -both on the local machine and the network -will be required to play back the file.
If you select VBR you will see 2 additional fields below the Target Data Rate.
Minimum will show you the lowest percentage that the data rate will go to. You can change this by typing in the percent box, and the data rate will calculate based off that percentage and the target.
Maximum is the opposite of Minimum, showing you the highest data rate that the video will go to for encoding more complex files.

Note: When creating MPEG-2 files for DVD authoring, It is important to remember that many DVD players won’t play files with data rates higher than 9000 Kbps, so it is important to make sure that both the target and the maximum data rates don’t get too close to the limit.


To finish explaining the Simple settings first, we will move over to the right column.

Frame Size
This specifies the width and height and aspect ratio policy of your movie. There are four choices of aspect ratio policy found in the Frame Size section:
Same As Source: This will output files with the same frame size as the source file. When this is selected, the Frame Size fields will become inactive.
Unconstrained: Allows you to freely change the width and height of the video at the expense of the aspect ratio. If the aspect ratio between the source and the output is different, then the video will be squished or stretched to comply with the newly entered settings.
Maintain Aspect Ratio: Constrains the video, so if you enter the width, the height is populated automatically, or vice versa. By default, the Maintain Aspect Ratio option is selected.
Letter Box or Pillar: Maintains the original size of the video and places black bars on the side of the video for pillar and on the top for letter box if the aspect ratio is different between the source frame size and the output frame size.

Advanced settings



The following settings are more complex, and should be only considered if the default settings are unsatisfactory. Clicking the Advanced button expands the dialog box further to provide options for advanced users. These features give you great looking digital video, even at very low data rates. We will go back to the Left column and work our way down.
Pixel Aspect Ratio
The Pixel Aspect ratio allows you to specify the shape of the pixels that are delivered in your MPEG file when it is viewed. You should select the pixel format that corresponds to the format in which your audience will view your files. Your choices are 4:3, 16:9, 2.21:1, and Square Pixel.

Note: The Squeeze Preview Window may not display the movie correctly if the pixels are not square. However the movie will be compressed correctly.

Field Encoding
The Field Encoding option allows you to apply interlacing to your output MPEG file. It is not available when you are creating MPEG-1 files (including the MPEG VCD Specifications). Options are Top field First, Bottom Field First, and Progressive.

GOP Structure Settings
In Video coding, a group of pictures, or GOP structure, specifies the order in which intra- and inter-frames are arranged.
GOP (group of picture) Settings will let you customize the order of the type of pictures (i.e. frames) according to your needs. A thorough explanation of GOP can be found here:
http://en.wikipedia.org/wiki/Group_of_pictures

I Frames
I-picture or I-frame (intra-coded picture) - reference picture, which represents a fixed image and which is independent of other picture types. Each GOP begins with this type of picture.
Changing this option allows you to place a key frame at the frequency identified in the drop-down list. If you want to encode a I-frame only video, which will yield the highest quality results with a high enough data rate, set the I frames to 1, which will change all the frames to I-frames.
P Frames
P-picture or P-frame (predictive coded picture) - contains motion-compensated difference information from the preceding I- or P-frame, and can only be decoded correctly if the previous I/P frame is available. P frames are smaller than I frames. If you set P frames to 1, all frames that aren’t I frames will be P frames, which will give you slightly higher quality than it would if you set the p frames to a longer interval.
B Frames
B-picture or B-frame (bidirectionally predictive coded picture) - contains difference information from the preceding and following I- or P-frame within a GOP. More b pictures allow for more compression and higher quality at lower bit rates and file sizes.
There isn’t a separate selection for B-frames, because, by default, any frames that aren’t designated to be an I frame or a P frame will be a B frame.

Example: If you set your I frames to 6 and P frames to 2, every other frame will be a B frame and your GOP will look like this in the example: IBPBPBIBPBPB


Auto GOP
This function always starts a new GOP when there is a scene change, i.e., the encoder sets an I frame. Selecting something other than none will give you a higher quality video output.
• None: If you choose None, a scene detection will not occur.
• Fast: The Fast option is a quick method of scene detection where no VCSD happens.
• VSCD: The abbreviation for Visual Content Scene Detection, which is a better way of doing scene detection. At first, the VSCD is carried out, i.e., the analysis of the frames, and then GOP planning. It will yield a slightly slower encoding.
Closed GOPS
This affects how each GOP interacts with the subsequent GOP. With a closed GOP, the B-Frame(s) at the end can only use data from the previous I or P-Frame With an open GOP, it can "look" beyond the GOP boundary for the data. As a result, the file will be slightly smaller.

Advanced MPEG Video Settings
The following article will give a detailed explanation of the difference in these settings:
http://en.wikipedia.org/wiki/H.262/M...les_and_levels
Profile ID
The profile defines the subset of features such as compression algorithm, chroma format, etc.
Level ID
The level defines the subset of quantitative capabilities such as maximum bit rate, maximum frame size, etc. The MPEG-2 spec (specification) allows for a large number of variations in the settings, e.g., the frame resolution can theoretically be as large as 214 x 214. The Profiles and Levels just set limits on what the values of some of the other settings can be; so if a specification (like the DVD spec) says only Main Profile/Main Level which only enables for a maximum frame resolution of 720x576.
Chroma ID
This allows you to change the color subsampling space. An in depth article on the subject can be found here:
http://en.wikipedia.org/wiki/Chroma_subsampling
The Chroma ID will be set to 4:2:0 unless the Profile ID is set to High or 4:2:2
Noise:
Sensitivity
Specifies how sensitive the video encoder is to noise in the source video; it does not reduce the noise in the source video at all. It sets a motion search threshold at which point the encoder will stop the search for matching blocks of pixels from one frame to another. Higher values mean low sensitivity (faster search times, less quality), while lower values mean higher sensitivity (longer search times, better quality). Typically this option is set in the 1 to 14 range as follow: 1 to 5 – Computer animation, VCD from DV-Source, after
a line-filter or noise reducing filter (virtually no noise in the source video) 3 to 7 – Digital video, DV-quality, Hi8-quality, etc. 5 to 14 – Analog captured video, Video 8, Hi8, broadcast TV The setting is strictly based on the state of the source video; it has nothing to do with the type of output (DVD, SVCD or VCD).
Reduction
This specifies the amount of noise reduction you want to apply to the output file. You can choose a value between 0 and 31.
Motion Search Mode
The Motion Search Mode defines which method is used to search for pixel movement in the video stream. A higher value specifies a better method and will normally yield better quality. You can choose something in the range of 0 and 15. The practical range is 3 to 11.

Now we will move back to the right column for the remainder of the Advanced settings.

Do half-pel search
When this option is activated the Motion Search operation also looks for pixels that move only half of a pixel from one frame to the next (a subpixel search). This should usually be enabled and should only be disabled if speed is desired above quality.
Enable Motion search Pixel movement
These settings specify the maximum movement of a pixel from one frame to the next. They are used to calculate the Motion Search Areas, the maximum area the encoder will search in an attempt to find a match for a block of pixels from one frame to the next. If the video has quite a bit of movement, it is useful to raise these values. Unfortunately, this also extends the encoding time. The motion search vectors are different and optimized for the different frames and frame types. Vertical and Horizontal can both be moved between the range of 0 and 2047.
Input video is RGB16-235
The checkbox Input video is RGB 16-235, particular black and white values are preserved. During encoding and decoding the RGB color space with R=G=b=16 is used, which corresponds to the color black. Furthermore, the RGB color space with R=G=B=235 is used, which corresponds to the color white. Normally the values for white are R=G=B=0, and for black R=G=B=255. The specification ITU601R now defines black (Y=16) and white (Y=256), i.e., the real video signal receives values which are “blacker than black” or “whiter than white” (so called super-black and super-white values). These super- black and super-white values get lost in the normal PC RGB 0..256 color space, but they are preserved with the Input video is RGB 16-235 option.
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