MPEG-4 Part 14 container
.mp4
MP4 video
A widely supported multimedia container used to package video, audio and other timed media. Actual playback depends on the codecs and features in the file.
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Video file formats and testing guide
Explore common video file types and learn how containers, codecs, audio tracks and subtitles work together. Use this guide to plan video upload, playback and compatibility tests.
.mp4.mov.mkv
Library
Explore common video formats
MP4, MOV and MKV are containers: they package encoded video and may also include audio, subtitles, chapters and metadata. The extension alone does not guarantee that every player supports the codecs inside.
QuickTime container
.mov
MOV video
The QuickTime movie container can hold media streams and metadata. Files with the same MOV extension may use different codecs, so check player requirements.
View MOV samplesMatroska container
.mkv
MKV video
The Matroska container can package video with multiple audio or subtitle tracks, chapters and metadata in one file. Support varies by device and playback software.
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Browse all file categories How digital video files work
A digital video file is more than a sequence of pictures. A container organizes the streams and descriptive data, while codecs encode and decode the picture and sound. Knowing the difference helps diagnose upload errors, missing audio, playback failures and format-conversion issues.
Container format and codec
The file extension usually identifies a container, not every encoding inside it. A video container can hold a video stream, audio streams, subtitles and metadata. A codec is the method used to encode or decode a stream, so two files with the same extension may behave differently in a particular player.
Resolution, frame rate and bitrate
Resolution describes the pixel dimensions of each frame. Frame rate describes how many frames are shown per second, and bitrate is one factor in file size and visual quality. Test files with different values help check scaling, playback performance, upload limits and bandwidth handling.
Audio, subtitles and metadata
Video containers may include one or more audio and subtitle tracks, timestamps, chapters or descriptive metadata. When validating a player or processing pipeline, check track selection, synchronization, captions and whether important file properties survive conversion.
Video file format questions
What is the difference between a video container and a codec?
A container packages streams and related information into a file. A codec encodes or decodes the video or audio stream stored in that container. The filename extension alone does not tell you every codec used.
Is MP4 a video codec?
MP4 is a multimedia container format, not a single video codec. It can contain video, audio, subtitle and other media streams encoded in supported ways.
Why can one player open a video while another cannot?
Players support different containers, codecs, profiles, audio formats and subtitle features. Check the stream details and player capabilities when the same file behaves differently across devices.
What should I check when testing a video file?
Check that the file opens, video and audio stay synchronized, the expected tracks and captions are available, the displayed duration and dimensions are correct, and upload or processing limits behave as expected.
Further reading: Wikipedia: video file format · Wikipedia: MP4 file format · Wikipedia: Matroska