3 ms·

MP4 is a container format. You can put an Excel spreadsheet in there if you want. I’m not sure what the author is getting at.

dna_polymerase 4y ago
Since most of us associate mp4 with moving images, what exactly is usually wrapped in the mp4 container, and is there a good introduction on the topic available?
- nimish 4y ago
  Audio and video. Wikipedia has a terse but comprehensive overview. It's comparable to Matroska (MKV). It's nearly identical to apple's QuickTime format: https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap1/qtff1.html https://developer.apple.com/library/archive/documentation/Qu...
  - CharlesW 4y ago
    > Audio and video. And images! The same container format¹ is used by AVIF. ¹ ISOBMFF (ISO base media file format), which is ISO/IEC 14496-12 (a.k.a. MPEG-4 Part 12).
- pjc50 4y ago
  Moving images. Generally in the form of a video stream (usually h264, but it can be anything), one or more audio stream (AAC or MP3), and a timestamp index that keeps them aligned and makes it easier to seek. It's not especially easy to find good documentation; people generally don't write software to touch it directly, either they use the OS media library or ffmpeg.
- wwader 4y ago
  If you want to go deep ISO-14496-12 is probably what your looking for. You can either pay ISO to read it or hypothetically you can google for "filetype:pdf ISO-14496-12". For how things actually work in practice https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/mov.c https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/mov... is a good resource.
  - Const-me 4y ago
    > For how things actually work in practice Another version of the demuxer, way simpler: https://github.com/Const-me/Vrmac/blob/master/VrmacVideo/Containers/MP4/Mp4Reader.cs https://github.com/Const-me/Vrmac/blob/master/VrmacVideo/Con... A complete mpeg4 media file, with enough features to play the content with hardware decoding: https://github.com/Const-me/Vrmac/blob/master/VrmacVideo/Containers/MP4/Mp4File.cs https://github.com/Const-me/Vrmac/blob/master/VrmacVideo/Con...
wwader 4y ago
It also has requirements on the box tree structure and order and what boxes are required/optional. Then there are also mapping per codec (see https://mp4ra.org/ https://mp4ra.org/) that have additional requirements on boxes and how the samples should be encoded. For example PNG in MP4 is mapped by having a stsd (sample descriptor) box that has a mp4v format/box which itself should includes a esds (mpeg elementary stream descriptor) box which will include a decode configuration stating that the stream type is video and the object type is PNG. You can see a decode using fq (https://github.com/wader/fq https://github.com/wader/fq) of the file used in the poster here https://twitter.com/mwader/status/1596219922304360448 https://twitter.com/mwader/status/1596219922304360448 Hope that was helpful

dna_polymerase 4y ago

Since most of us associate mp4 with moving images, what exactly is usually wrapped in the mp4 container, and is there a good introduction on the topic available?

nimish 4y ago
Audio and video. Wikipedia has a terse but comprehensive overview. It's comparable to Matroska (MKV). It's nearly identical to apple's QuickTime format: https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap1/qtff1.html https://developer.apple.com/library/archive/documentation/Qu...
- CharlesW 4y ago
  > Audio and video. And images! The same container format¹ is used by AVIF. ¹ ISOBMFF (ISO base media file format), which is ISO/IEC 14496-12 (a.k.a. MPEG-4 Part 12).
pjc50 4y ago
Moving images. Generally in the form of a video stream (usually h264, but it can be anything), one or more audio stream (AAC or MP3), and a timestamp index that keeps them aligned and makes it easier to seek. It's not especially easy to find good documentation; people generally don't write software to touch it directly, either they use the OS media library or ffmpeg.
wwader 4y ago
If you want to go deep ISO-14496-12 is probably what your looking for. You can either pay ISO to read it or hypothetically you can google for "filetype:pdf ISO-14496-12". For how things actually work in practice https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/mov.c https://github.com/FFmpeg/FFmpeg/blob/master/libavformat/mov... is a good resource.
- Const-me 4y ago
  > For how things actually work in practice Another version of the demuxer, way simpler: https://github.com/Const-me/Vrmac/blob/master/VrmacVideo/Containers/MP4/Mp4Reader.cs https://github.com/Const-me/Vrmac/blob/master/VrmacVideo/Con... A complete mpeg4 media file, with enough features to play the content with hardware decoding: https://github.com/Const-me/Vrmac/blob/master/VrmacVideo/Containers/MP4/Mp4File.cs https://github.com/Const-me/Vrmac/blob/master/VrmacVideo/Con...

wwader 4y ago

It also has requirements on the box tree structure and order and what boxes are required/optional. Then there are also mapping per codec (see https://mp4ra.org/ https://mp4ra.org/) that have additional requirements on boxes and how the samples should be encoded. For example PNG in MP4 is mapped by having a stsd (sample descriptor) box that has a mp4v format/box which itself should includes a esds (mpeg elementary stream descriptor) box which will include a decode configuration stating that the stream type is video and the object type is PNG. You can see a decode using fq (https://github.com/wader/fq https://github.com/wader/fq) of the file used in the poster here https://twitter.com/mwader/status/1596219922304360448 https://twitter.com/mwader/status/1596219922304360448 Hope that was helpful