What Is MP4? The Universal Video Format Explained
MP4, formally known as MPEG-4 Part 14, is the most widely used video container format in the world. Standardized by the ISO in 2001 and updated in 2003, it can hold video, audio, subtitles, and still images within a single file. Its combination of efficient compression, broad device support, and streaming-friendly design has made it the default choice for everything from YouTube videos to smartphone recordings.
Technical Overview of the MP4 Container
MP4 is a container format, not a codec. This distinction is important: the container defines how data streams are packaged together, while codecs determine how the actual video and audio are compressed. An MP4 file typically wraps H.264 (AVC) or H.265 (HEVC) video alongside AAC audio, though it also supports older codecs like MPEG-4 Part 2 and newer ones such as AV1.
The MP4 container is based on the Apple QuickTime MOV format and uses a hierarchical atom (or box) structure. Each atom contains metadata about the media streams, including timing information, codec parameters, and sample tables that map byte offsets to individual frames. This structure enables efficient random access and seeking, which is critical for both local playback and progressive streaming over HTTP.
MP4 supports multiple audio and video tracks, embedded subtitles in formats like MPEG-4 Timed Text, chapter markers, and extensive metadata through the iTunes-style tagging system. The file extension is typically .mp4 for video content, though .m4a is used for audio-only files and .m4v for DRM-protected video.
Advantages and Limitations of MP4
MP4 has become dominant for good reasons, but it does come with certain trade-offs worth understanding.
- Near-universal playback support across browsers, smartphones, smart TVs, gaming consoles, and media players
- Excellent compression efficiency when paired with H.264 or H.265, producing small files with high visual quality
- Native streaming support: the moov atom can be placed at the file start for instant web playback without full download
- Supports multiple audio tracks, subtitle streams, and chapter markers in a single file
- Widely accepted by social media platforms, video hosting services, and messaging apps
- Limited subtitle format support compared to MKV, which handles SRT, ASS, and PGS natively
- Does not support some niche codecs like VP9 as gracefully as WebM or MKV containers
- DRM implementations vary across platforms, leading to compatibility issues with protected content
MP4 vs MKV: Choosing the Right Container
MP4 and MKV are the two most popular video containers. Their strengths serve different use cases.
| Feature | MP4 | MKV |
|---|---|---|
| Device compatibility | Plays on virtually every device | Requires software player on some devices |
| Subtitle support | Limited to MPEG-4 Timed Text | Supports SRT, ASS, PGS, VobSub, and more |
| Streaming | Excellent for web streaming | Not designed for streaming |
| Multiple audio tracks | Supported but less common | Commonly used for multiple languages |
| Codec flexibility | H.264, H.265, AAC primarily | Supports nearly any codec |
| File size | Slightly smaller container overhead | Minimal overhead difference |
How to Convert Videos to MP4
- 1
Select your source video
Choose the video file you want to convert. MP4 conversion works with virtually any input format including AVI, MKV, MOV, WebM, and WMV.
- 2
Pick your target quality
Decide on the resolution and quality level. For web sharing, 1080p with standard quality is usually sufficient. For archival, keep the original resolution.
- 3
Upload and convert
Use an online tool like WeLoveConvert to upload your file. Browser-based conversion keeps your files private since nothing is sent to a server.
- 4
Download the MP4 file
Once the conversion finishes, download your new MP4 file. It will be ready to play on any device or upload to any platform.
Recommended MP4 Encoding Settings
These settings provide a solid starting point for common MP4 encoding scenarios.
The most compatible video codec. Use H.265 only if you need smaller files and your target devices support it.
AAC Low Complexity offers excellent quality and universal support. 128 kbps stereo is fine for most content.
Constant Rate Factor controls quality. Lower values mean better quality and larger files. CRF 23 is the default; 18 is visually lossless.
Slower presets produce smaller files at the same quality but take longer to encode. Medium is a good balance.
Required for maximum compatibility. Some players cannot decode yuv444p or yuv422p content.
The History and Future of MP4
The MP4 format traces its lineage to the Apple QuickTime file format, which was adapted and standardized by the ISO as part of the MPEG-4 specification. The initial standard, ISO/IEC 14496-14, was published in 2003 and built upon the ISO Base Media File Format (ISO/IEC 14496-12). This shared foundation means that MP4, MOV, and 3GP files are structurally similar.
MP4 rose to dominance in the mid-2000s as H.264 video compression became the standard for web video, Blu-ray discs, and mobile devices. YouTube, Netflix, and virtually every streaming platform adopted MP4 with H.264 as their primary delivery format. The introduction of H.265/HEVC in 2013 brought further compression improvements, roughly halving file sizes at the same quality, though adoption was slowed by complex patent licensing.
Looking ahead, MP4 continues to evolve. The container now supports AV1, a royalty-free codec backed by the Alliance for Open Media, which promises even better compression than H.265. As AV1 hardware decoding becomes widespread, MP4 with AV1 video and Opus audio may become the next standard combination for web video delivery.
Frequently Asked Questions
What is the difference between MP4 and MPEG-4?
MPEG-4 is a broad multimedia standard covering video codecs, audio codecs, and container formats. MP4 specifically refers to Part 14 of the MPEG-4 standard, which defines the container format. The MPEG-4 Part 2 video codec is just one of many codecs that can be stored inside an MP4 container.
Can MP4 files contain subtitles?
Yes, MP4 supports embedded subtitles using the MPEG-4 Timed Text format (also called tx3g). However, it does not natively support popular subtitle formats like SRT or ASS. For those, MKV is a better container choice.
Is MP4 lossy or lossless?
MP4 is a container, not a codec, so it can hold both lossy and lossless content. Most MP4 files use lossy H.264 video and AAC audio for practical file sizes. However, you can store lossless codecs like Apple ProRes or FLAC inside an MP4 container.
Why is my MP4 file so large?
File size depends on the codec, resolution, bitrate, and duration. If your MP4 uses a high bitrate or an inefficient codec, it will be large. Re-encoding with H.264 at CRF 23 or switching to H.265 can significantly reduce file size with minimal quality loss.
Can I play MP4 on any device?
MP4 with H.264 video and AAC audio plays on virtually every modern device including smartphones, tablets, computers, smart TVs, and gaming consoles. Older devices may struggle with H.265 or AV1 encoded MP4 files.
What is the moov atom in MP4?
The moov atom is a metadata structure containing information about all tracks in the file, including codec details, timing, and sample locations. For web streaming, the moov atom should be placed at the beginning of the file (fast start) so the player can begin playback before downloading the entire file.
Is MP4 better than MOV?
MP4 and MOV are structurally very similar since MP4 is derived from the QuickTime format. MP4 has broader compatibility across non-Apple devices and platforms. MOV is preferred in Apple professional workflows. For general distribution, MP4 is the safer choice.
Does MP4 support 4K and HDR video?
Yes. MP4 fully supports 4K, 8K, and HDR content when paired with appropriate codecs like H.265 or AV1. HDR metadata such as HDR10 and Dolby Vision can be stored in the MP4 container alongside the video stream.
MP4 has earned its place as the universal video format through a combination of excellent compression, broad compatibility, and streaming-friendly design. Whether you are sharing clips on social media, encoding a video library, or publishing content to the web, MP4 with H.264 or H.265 remains the most reliable choice. As newer codecs like AV1 mature, the MP4 container will continue to adapt, ensuring its relevance for years to come.