Fragment MP4 File Format

At present, there have been a lot of summaries on the MP4 file format on the network. I will not copy the summary from others here. If you want to get started, Baidu will have a lot of such content.Article. Here we will introduce one of the MP4 file structures rarely involved in other articles, namely, fragment MP4, which is also called ismv files.

If you really want to know the MP4 file format, you can learn about an open-source tool project: MP4 explorer. On the one hand, this tool can follow the MPEG-4 standard to parse MP4 files, intuitive help you to see the MP4 file format. On the other hand, study it carefullyCodeTo learn how MP4 files are accessed and accessed. It is a good news for those who are committed to underlying research. Its official website: http://mp4explorer.codeplex.com/

This document describes an MP4 File Format called fragmented MP4 (fmp4 for short. The file format is different from the MP4 file. The following two images are used for comparison.

Figure 1 physical structure of a common MP4 File

Figure 2 fragmented MP4 file structure

The following describes the advantages and disadvantages of the two formats.

For the first format, the meta data of the entire MP4 file is in the file header, and all media data is a whole piece. When the file size is large, the meta data size is large. In this way, there is no problem in playing MP4 files locally. However, for some video playback websites, the user's player must download Full Meta data to start playing. This means that the user's buffer time will be extended due to the storage structure of MP4 files. Currently, one solution is to cut large MP4 files into multiple segments physically separated, so that the meta of each segment is relatively small, thus reducing the buffer time to a certain extent.

For the second format, MP4 files are divided into multiple frag fragments, while the original meta data is greatly reduced, and no frag can be separately indexed, transmitted, and played, this will solve the problem that MP4 cannot stream play. Better user experience. However, this format is not fully supported by most decoders. Some players load files for a long time, and the embedded player in the browser may not support playback.

Microsoft launched this solution before the 08 Olympic Games and applied it to NBC livevideo. For more information about the technology, see the following link: introduction of NLP.