The previous explanations were very broadcast-oriented, in OTT, however, there are special considerations to be made. OTT clients have network connections that are unstable and do not have a guaranteed bandwidth which requires that only content that will be presented should be loaded. Given that a client is only able to present a single program at a time, having multiple programs in the same transport stream and loading them would be a waste of bandwidth that could be better used otherwise, e.
So for OTT we would never have multiple programs in one transport stream. For multi-audio content similar arguments apply regarding multiplexing elementary streams, i. MPEG-TS is transport-oriented and includes considerations for lossy communication channels which is not exactly a good fit for HTTP-based media delivery where transport loss is already handled by the network stack.
Matroska is a free and open-standard container format. This fact makes the standard easy to extend. It is possible to virtually support any codec. WebM is based on the Matroska container format. A separate process is required to synchronise the two streams. It is designed to be robust with short frames, each one being protected by a strong error correction mechanism. It is constructed to match the characteristics of the generic radio or cable channel and expects an uncorrected Bit Error Rate BER of better than 10 The different variants of DVB each have their own outer coding and modulation methods designed for the particular environment.
It is not, in itself, a transport layer protocol and no mechanism is provided to ensure the reliable delivery of the transported data. MPEG-2 relies on underlying layers for such services. A TS may correspond to a single TV program, or multimedia stream e. Each PES shares a common timebase. This larger aggregate also contains all the control information Program Specific Information PSI required to co-ordinate the DVB system, and any other data which is to be sent.
Most transport streams consist of a number of related elementary streams e. The decoding of the elementary streams may need to be co-ordinated synchronised to ensure that the audio playback is in synchronism with the corresponding video frames. Each stream may be tightly synchronised usually necessary for digital TV programs, or for digital radio programs , or not synchronised in the case of programs offering downloading of software or games, as an example.
To help synchronisation time stamps are sent in the transport stream. For a user to receive a particular transport stream, the user must first determine the PID being used, and then filter packets which have a matching PID value.
Because VBrick sends a Single Program Transport Stream, we have a special capability to automatically detect the PID and automatically configure the decoder to display the correct content. To help the user identify which PID corresponds to which program, a special set of streams, known as Signalling Tables , are transmitted with a description of each program carried within the MPEG-2 Transport Stream.
Signalling tables are sent separately to PES, and are not synchronised with the elementary streams i. The tables called Program Specific Information PSI in MPEG-2 consist of a description of the elementary streams which need to be combined to build programs, and a description of the programs. PES packets. Each section is protected by a CRC checksum to verify the integrity of the table being carried. The length of a section allows a decoder to identify the next section in a packet. A PSI section may also be used for down-loading data to a remote site.
Tables are sent periodically by including them in the transmitted transport multiplex. This lists all programs in the multiplex. There is one PMT per program. DVB also adds a number of additional tables. The presence of an adaptation field is indicated by the adaption field control bits in a transport stream packet. If present, the adaption field directly follows the 4 B packet header, before any user payload data. It may contain a variety of data used for timing and control.
The Letterbox Area of Source option detects image edges and automatically enters crop values to match them. This is useful if you want to crop out the letterbox area the black bars above and below a widescreen image of a source media file. The custom option allows you to enter your own scaling dimensions in the fields; other options use predetermined dimensions.
The following properties determine how Compressor resizes, retimes, and otherwise adjusts the video when transcoded:. Nearest Pixel Fastest : Samples the nearest neighboring pixel when resizing an image.
This option provides the fastest processing time, but it is more likely to show aliasing artifacts and jagged edges.
Linear: Adjacent pixel values are averaged using a linear distribution of weights. Produces fewer aliasing artifacts than Nearest Pixel, with a small increase in processing time. Gaussian: Adjacent pixel values are averaged using a gaussian distribution of weights.
This provides a medium trade-off between processing time and output quality. Lanczos 2: Adjacent pixel values are averaged using a truncated sinc function. This option is slower than Gaussian but provides sharper results.
Lanczos 3: Similar to Lanczos 2 but averages more pixel values. This option is slower than Lanczos 2 but may produce better results. Bicubic: Adjacent pixel values are averaged using a bicubic function. The processing time and output are most similar to Lanczos 2 and Lanczos 3. Anti-aliased Best : Provides the highest output quality, but can take substantially longer to process. Good Frame Blending : Blends neighboring frames using a filter to produce good-quality interpolation.
Best Motion Compensated : Uses optical flow to interpolate using areas of movement between neighboring frames to produce high-quality output. Choosing this item disables all the other Quality controls.
See Use reverse telecine in Compressor. Adaptive details: Select this checkbox to use advanced image analysis to distinguish between noise and edge areas during output. Anti-aliasing level: Sets the softness level in the output image. Double-click the value and then manually enter a new value or drag the slider to the right to increase softness.
For example, when transcoding SD video to HD, anti-aliasing smooths jagged edges that might appear in the image. Details level: Sets the amount of detail in the output image. Double-click the value and then manually enter a new value or drag the slider to set the value.
This sharpening control lets you add detail back to an image being enlarged. Dithering: When selected, adds a certain type of noise to images to prevent large-scale distracting patterns such as color banding. If your image has excessive noise after rendering, deselect this checkbox. For a list of available video effects in Compressor, and instructions on how to add a video effect to a setting, see Add and remove effects in Compressor.
Setting summary Displays the setting name and transcoding format used by Compressor, as well as an estimated output file size. General properties Name: Displays the name of the setting. Description: Displays the description of the setting. Extension: Displays the extension of the output file. Compressor modifies the available properties based on the option you choose: Generic: This option allows you complete access to all the MPEG-2 properties.
Retiming Sets the processing algorithm used to adjust the frame rate during transcoding. Video properties Frame size: Use this pop-up menu to set the frame size resolution for the output file.
Manual: Forces the output to a specific resolution. Constrained: Constrains the output to a specific aspect ratio. There are four options: Automatic: Selects the most appropriate field order, based on the field order of the source and the capabilities of the selected codec.
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