Video File Containers Explained: MKV, AVI, MOV, and More

Container vs. Codec: Understanding the Difference

When discussing video files, two terms frequently cause confusion: container and codec. Many people use these interchangeably, but they serve distinct functions:

The Shipping Box Analogy

Think of a video file as a shipping box:

• Container (the box): The file format that holds everything together—video, audio, subtitles, metadata. Examples: MP4, MKV, AVI, MOV
• Codec (the contents): The compression technology that reduces file sizes. Examples: H.264, H.265, VP9, AAC, MP3

Just as a cardboard box can hold different items (books, electronics, clothing), a video container can hold different codecs. An MP4 file might contain H.264 video with AAC audio, or H.265 video with Opus audio—same container, different contents.

Key insight: When you download a video using SSDown, both the container and codec are determined by the source platform. Understanding containers helps you choose compatible formats for your devices.

What Does a Container Do?

A video container is responsible for:

1. Multiplexing: Combining separate video, audio, and subtitle streams into a single file
2. Synchronization: Ensuring audio stays in sync with video during playback
3. Metadata storage: Holding information about title, duration, resolution, creation date, etc.
4. Chapter markers: Supporting navigation points within long videos
5. Subtitle/caption support: Embedding or referencing text tracks
6. Multiple audio tracks: Supporting different languages or audio formats in one file
7. Streaming support: Enabling progressive download or adaptive streaming

Major Video Container Formats

MP4 (MPEG-4 Part 14)

Overview: The most widely used container format, based on Apple's QuickTime MOV format.

Pros:

• Universal compatibility across all devices and platforms
• Excellent streaming support for web playback
• Small overhead (efficient file size)
• Industry standard for distribution

Cons:

• Limited subtitle format support
• Cannot store some advanced features (detailed chapters, extensive metadata)
• Proprietary format (requires licensing for commercial software)

Best for: General distribution, social media, streaming, mobile devices, maximum compatibility

MKV (Matroska Video)

Overview: Open-source container designed to be future-proof and feature-rich.

Pros:

• Open source and royalty-free
• Supports virtually any codec combination
• Excellent subtitle and chapter support
• Can hold unlimited audio/subtitle tracks
• Future-proof (extensible format)
• Robust error recovery

Cons:

• Limited device compatibility (TVs, game consoles often don't support it)
• Not ideal for streaming (larger overhead)
• Some software doesn't support all MKV features

Best for: Archiving, high-quality video collections, multi-language content, content with extensive subtitles

AVI (Audio Video Interleave)

Overview: Microsoft's legacy container format from 1992, still widely used but showing its age.

Pros:

• Extremely wide compatibility (plays on virtually anything)
• Simple structure (easy to repair corrupted files)
• Predictable behavior across systems

Cons:

• File size limit (2 GB for standard AVI, 4 GB for AVI 2.0)
• Poor compression efficiency
• No native subtitle support
• Limited codec support
• Outdated technology

Best for: Legacy systems, compatibility with old devices, simple video editing projects

MOV (QuickTime File Format)

Overview: Apple's proprietary container, the basis for MP4.

Pros:

• Excellent compatibility with Apple ecosystem
• Supports professional codecs (ProRes, DNxHD)
• High-quality video editing standard
• Advanced features (timecode, metadata)

Cons:

• Limited compatibility outside Apple devices
• Often larger file sizes than MP4
• Requires QuickTime codecs on Windows

Best for: Apple ecosystem, professional video editing, high-quality archival, Final Cut Pro projects

WebM

Overview: Google's open-source container optimized for web streaming.

Pros:

• Completely open source and royalty-free
• Excellent compression with VP9/AV1
• Native browser support (Chrome, Firefox, Edge)
• Optimized for web streaming

Cons:

• Limited Safari/iOS support
• Smaller codec selection (VP8/VP9/AV1 only)
• Less suitable for offline archival

Best for: Web video, HTML5 streaming, open-source projects, YouTube content

Complete Container Comparison Table

Codec Compatibility by Container

Not all codecs work in all containers. Here's what combinations are possible:

Container Overhead Comparison

Containers add overhead—extra data for metadata, synchronization, and structure. Here's how much:

MP4 and WebM have the smallest overhead, making them most efficient for storage and streaming.

Converting Between Containers

Sometimes you need to change containers without re-encoding (which loses quality). This is called remuxing—copying streams from one container to another.

Lossless Remuxing Possibilities

FFmpeg Remuxing Example

To remux MKV to MP4 without re-encoding (lossless, fast):

ffmpeg -i input.mkv -c copy output.mp4

This completes in seconds rather than minutes/hours because it's just copying streams, not re-encoding.

Which Container Should You Choose?

Decision Tree

1. Do you need maximum compatibility? → Use MP4
2. Are you archiving high-quality content with multiple audio/subtitle tracks? → Use MKV
3. Is this for the Apple ecosystem? → Use MOV
4. Is this for web streaming only? → Use WebM (if Safari support not needed) or MP4
5. Do you need compatibility with very old devices? → Use AVI

Recommendations by Use Case

How Social Media Platforms Use Containers

When you download videos using SSDown, here's what container formats different platforms provide:

Notice that MP4 dominates social media because of its universal compatibility and streaming efficiency.

Conclusion

Video containers are the packaging that holds your video, audio, and subtitle streams together. While the codec determines quality and file size, the container determines compatibility and feature support. For most users:

• MP4 is the safe default—maximum compatibility, excellent streaming, efficient overhead
• MKV is ideal for archiving—open source, feature-rich, supports any codec
• MOV is best for Apple users—professional features, ecosystem integration
• WebM is perfect for web-only content—efficient, open source, browser-native

When downloading videos with SSDown, the container is chosen by the source platform. Understanding containers helps you make informed decisions about whether to convert formats and which devices will play your downloads smoothly.