MP4 for Streaming

Streaming services are now part of our everyday life, and it’s all thanks to MP4. This computer standard allows videos to be played online and on various devices. Jean-Claude Dufourd and Jean Le Feuvre, researchers in Computer Science at Télécom Paris, have been recognized by the Emmy Awards Academy for their work on this computer format amongst other things.

In 2021 the File Format IT working group of the MPEG Committee received an Emmy Award for its work in developing ISOBMFF. Behind this term lies a computer format that was used as the basis for the development of MP4, the famous video standard we have all encountered when saving a file in the ‘.mp4’ format. “The Emmy’s decision to give an award to the File Format group is justified; this file format has had a great impact on the world of video by creating a whole ecosystem that brings together very different types of research,” explains Jean-Claude Dufourd, a computer scientist at Télécom Paris and a member of the File Format group.

MP4, which can capture sound and also video, “is used for live or on-demand media broadcasting, but not for the real-time broadcasting needed to stream games or video conferences,” explains Jean Le Feuvre, also a computer scientist at Télécom Paris and member of the File Format group. There are several features of this format that have contributed to its success, including the ability to capture long videos like movies, while still remaining very compact.

The smaller the file size, the easier they are to circulate on networks. The compactness of MP4 is therefore an advantage for streaming movies and series.  Another explanation for its success is its adaptability to different types of devices. “This technology can be used on a wide variety of everyday devices such as telephones, computers, and televisions,” explains Jean-Claude Dufourd. The reason that MP4 is playable on different devices is because “the HTTP file distribution protocol has been reused to distribute video,” says the researcher.

Improving streaming quality

The HTTP (Hypertext Transfer Protocol), which has been prevalent since the 1990s, is typically used to create websites. Researchers have modified this protocol so that it can be used to broadcast video files online. Their studies led to the development of HTTP streaming, and then to an improved version called DASH (Dynamic Adaptive Streaming over HTTP), a protocol that “cuts up the information in the MP4 file into chunks of a few seconds each,” says Jean-Claude Dufourd. The segments obtained at the end of this process are successfully retrieved by the player to reconstruct the movie or the episode of the series being watched.

This cutting process allows the playback of the video file to be adjusted according to the connection speed. “For each time range, different quality encoding is provided, and the media player is responsible for deciding which quality is best for its conditions of use,” explains Jean Le Feuvre. Typically, if a viewer’s connection speed is low, the streaming player will select the video file with the least amount of data in order to facilitate traffic. The player will therefore select the lowest streaming quality. This feature allows content to continue playing on the platform with minimal risk of interruption.

In order to achieve this ability to adapt to different usage scenarios, tests have been carried out by scientists and manufacturers. “Tests were conducted to determine the network profile of a phone and a computer,” explains Jean-Claude Dufourd. “The results showed that the profiles were very different depending on the device and the situation, so the content is not delivered with the same fluidity,” he adds.

Economic interests

“Today, we are benefiting from 15 years of technological refinement that have allowed us to make the algorithms efficient enough to stream videos,” says Jean-Claude Dufourd. Since the beginning of streaming, one of the goals has been to broadcast videos with the best possible quality, while also reducing loading lag and putting as little strain on the network capacity as possible.

The challenge is primarily economic; the more strain that streaming platforms put on network capacity to stream their content, the more they have to pay. Currently, people are studying how to reduce the broadcaster’s internet bill. One solution would be to circulate video files mainly among users, thereby creating a less centralized streaming system. This is what file sharing systems allow between users (P2P or Peer-to-Peer networks). This alternative is currently being considered by streaming companies, as it would reduce the cost of broadcasting content.  

Rémy Fauvel