Everyone can build a transcoding ladder, but it requires experimentation and adjustements with codecs, target and delivery methods. It's a frequent topic for encoding experts like Jan Ozer
Is a one-size-fits-all encoding ladder strategy for adaptive bitrate streaming relevant, or should it adapt to the devices used (mobile, tablet, computer, set-top box)?
Short answer: No.
In the case of adaptive bitrate streaming, a one-fits-all encoding ladder strategy may not always be relevant, as different devices may have different capabilities and limitations when it comes to streaming video content.
Adaptive bitrate streaming is a technique used to deliver video content over the internet, where the video quality is adapted to the available network conditions and the capabilities of the playback device. This is achieved by encoding the video content at multiple bitrates, and then dynamically switching between these different bitrates based on the network conditions and the capabilities of the playback device.
To optimize the performance of adaptive bitrate streaming, it is important to tailor the encoding ladder strategy to the specific capabilities of the playback devices being used. For example, a mobile device with a smaller screen and limited processing power may require a lower bitrate and a more efficient encoding scheme than a desktop computer with a larger screen and more processing power.
Therefore, it is crucial to consider the characteristics of the devices that are likely to be used for streaming the video content, such as screen size, processing power, and available bandwidth, and then optimize the encoding ladder strategy accordingly. This may involve using different encoding settings or bitrates for other devices or adapting the encoding ladder on the fly based on real-time feedback from the playback device.
What are the methods for implementing a unique transcoding ladder for each device?
To provide a different per-device transcoding ladder in adaptive bitrate streaming, manifest manipulation is a key technique that can be used. A manifest is a file that describes the available video streams and the different bitrates that are available for each stream. The manifest is typically generated by the streaming server and is downloaded by the client device before the video playback begins.
There are different ways to implement a different per-device transcoding ladder using manifest manipulation. One approach is to generate multiple manifests, each tailored to a specific device type, and then serve the appropriate manifest based on the user agent string of the client device.
Another approach is to use a single manifest, but include multiple renditions of the video content, each optimized for a different device type. In this case, the client device can choose the appropriate rendition based on its capabilities and network conditions.
To implement this approach, the streaming server can use a video transcoding service to generate multiple renditions of the video content at different bitrates and resolutions. The server can then include these different renditions in the manifest file, along with information about the bitrate, resolution, and other characteristics of each rendition.
When the client device requests the manifest file, it can examine the available renditions and choose the one that is best suited to its capabilities and network conditions. The client device can then download and play back the chosen rendition, and switch to a different rendition if the network conditions change.
Is 144p QCIF resolution still useful nowadays?
The 144p QCIF (Quarter Common Intermediate Format) resolution, which has a resolution of 176x144 pixels, is a very low resolution by today's standards. It was commonly used in the early days of digital video for mobile devices and low-end digital cameras, but it has since been largely superseded by higher resolutions.
In today's world, where high-definition (HD) and ultra-high-definition (UHD) video content are becoming more and more popular, it is unlikely that 144p QCIF resolution would be considered useful for most applications. However, there may still be some specialized use cases where this resolution is relevant, such as:
Bandwidth-limited applications: In some situations, such as in areas with poor network connectivity or on mobile devices with limited data plans, lower resolutions may still be useful to reduce bandwidth requirements and improve playback performance.
Surveillance and security: Some surveillance and security cameras still use lower resolutions to reduce the storage requirements and allow for longer retention periods of video footage.
Low-cost applications: In some cases, where cost is a significant factor, lower resolutions may still be useful for low-end devices or applications where video quality is not a primary concern.
In general, however, 144p QCIF resolution is unlikely to be useful for most mainstream video applications, where higher resolutions and better image quality are expected.
What aspects should you pay attention to for pristine video quality?
A transcoder that uses dividers of 1080p or 720p is a better choice for avoiding pixel interpolation because it ensures that the video content is evenly scaled down to a lower resolution without any pixel interpolation or scaling artifacts.
Pixel interpolation is a technique used to scale images or videos to a higher or lower resolution by creating new pixels based on the information from adjacent pixels. While this technique can be useful for scaling images or videos to some extent, it can also introduce scaling artifacts such as blurriness, jagged edges, and color distortion.
When scaling down a video to a lower resolution, it is important to ensure that the scaling is done in an even and consistent manner to avoid any scaling artifacts. Using dividers of 1080p or 720p ensures that the scaling is done in a consistent and even manner, without any fractional scaling factors that could result in pixel interpolation.
For example, if a video with a resolution of 1920x1080 (1080p) is scaled down to a resolution of 960x540, which is half the width and half the height of 1080p, the scaling can be done in a simple and even manner by simply dropping every other row and every other column of pixels. This results in a resolution of 960x540 that is evenly scaled down from 1080p, without any pixel interpolation or scaling artifacts.
Similarly, if a video with a resolution of 1280x720 (720p) is scaled down to a resolution of 640x360, which is half the width and half the height of 720p, the scaling can be done in a simple and even manner by dropping every other row and every other column of pixels. This results in a resolution of 640x360 that is evenly scaled down from 720p, without any pixel interpolation or scaling artifacts.
For this reason, analog-age resolutions like 576p or 144p should be removed from any stream.
In summary, using dividers of 1080p or 720p ensures that the scaling of video content to a lower resolution is done in an even and consistent manner, without introducing any pixel interpolation or scaling artifacts.