Containers vs codecs: the key difference
Before comparing formats, it's important to understand the difference between a container and a codec:
- Container (MP4, MKV, WebM, MOV) — the "box" that holds the video, audio, subtitles, and metadata tracks together in one file
- Codec (H.264, H.265, VP9, AV1) — the compression algorithm used to encode the actual video data
The same video codec can be stored in different containers. For example, H.264 video works in MP4, MKV, and MOV containers. The container affects compatibility and features, while the codec affects quality and file size.
Format comparison at a glance
| Format | Best for | Mac support | Web support | Subtitle tracks |
|---|---|---|---|---|
| MP4 | Universal sharing | Native (QuickTime) | All browsers | Limited |
| MKV | Archiving, multi-track | VLC/IINA needed | No | Unlimited |
| WebM | Web/YouTube | Chrome/VLC | Most browsers | Limited |
| MOV | Apple ecosystem | Native (QuickTime) | Safari only | Limited |
| AVI | Legacy compatibility | VLC needed | No | No |
MP4 — the universal standard
MP4 (MPEG-4 Part 14) is the most widely supported video format. It plays natively on every Mac, iPhone, iPad, Android device, Windows PC, and web browser. If you need to share a video and want it to "just work" everywhere, MP4 is the right choice.
- Pros: Universal compatibility, hardware-accelerated playback, works with all editors
- Cons: Limited to one subtitle track, doesn't support all codecs (no VP9 officially)
- Common codecs: H.264, H.265 (HEVC), AAC audio
- Best for: Sharing, uploading, general use
MKV — the feature-rich container
MKV (Matroska) is an open-source container that supports virtually any codec and unlimited tracks. You can have multiple audio tracks (different languages), multiple subtitle tracks, chapter markers, and more — all in one file.
- Pros: Supports all codecs, unlimited tracks, chapters, open-source
- Cons: Not natively supported by QuickTime/Finder preview (needs VLC or IINA)
- Common codecs: H.264, H.265, VP9, AV1, FLAC audio
- Best for: Archiving, multi-language content, downloaded videos with subtitles
Tip: If you download a video in MKV format and want to play it natively on Mac, use Star Video Downloader's Convert tab to remux it to MP4. If the codecs are compatible (H.264/H.265), the conversion is instant with zero quality loss.
WebM — Google's web format
WebM is Google's open format designed for web video. YouTube uses WebM internally for VP9 and AV1 encoded streams. When you download 4K YouTube videos, you'll often get WebM files.
- Pros: Excellent compression (VP9/AV1), open-source, good browser support
- Cons: Not supported by QuickTime, limited device compatibility
- Common codecs: VP9, AV1, Opus audio
- Best for: Web embedding, YouTube downloads at highest quality
MOV — Apple's format
MOV is Apple's QuickTime format. It's essentially the same as MP4 (both are based on the ISO base media file format) but with some Apple-specific extensions. MOV files play perfectly on Mac but may have compatibility issues on non-Apple devices.
- Pros: Native Mac/iOS support, works great with Final Cut Pro and iMovie
- Cons: Less universal than MP4, larger file sizes with ProRes codec
- Common codecs: H.264, H.265, ProRes, AAC audio
- Best for: Apple ecosystem, video editing on Mac
AVI — the legacy format
AVI (Audio Video Interleave) is Microsoft's legacy format from 1992. It still works but lacks modern features like streaming, chapters, and efficient compression. There's rarely a reason to use AVI for new content.
- Pros: Wide legacy support
- Cons: Large file sizes, no subtitle support, no modern codecs, no streaming
- Best for: Compatibility with very old software or devices
Which format should you choose?
- For sharing or uploading: MP4 (H.264) — works everywhere
- For archiving with subtitles: MKV — preserves all tracks and metadata
- For Mac-only use: MOV or MP4 — both work natively
- For web embedding: WebM (VP9) — best compression for web
- For highest quality from YouTube: Download in WebM/MKV (VP9/AV1), convert to MP4 if needed
Converting between formats on Mac
Star Video Downloader includes a built-in format converter (Pro feature) powered by ffmpeg. You can convert between MP4, MKV, WebM, MOV, AVI, and more. Two types of conversion:
- Remux (instant, lossless): Changes the container without re-encoding. Works when source and target support the same codec (e.g., MKV → MP4 with H.264). Zero quality loss, takes seconds.
- Re-encode (slower, slight quality change): Converts the actual video data. Required when changing codecs (e.g., VP9 → H.264). Takes longer but produces universally compatible files.
Frequently Asked Questions
Which video format is best for Mac?
MP4 (H.264) offers the best compatibility on Mac — it plays natively in QuickTime, Safari, and all Apple apps. MOV is Apple's own format and works just as well. For maximum quality with smaller files, MP4 with H.265 (HEVC) is ideal for Apple Silicon Macs.
What's the difference between a container and a codec?
A container (MP4, MKV, WebM) is like a box that holds the video and audio tracks. A codec (H.264, VP9, AV1) is the compression method used to encode the actual video data. The same codec can be stored in different containers.
Can I convert between video formats without losing quality?
Yes — if you remux (change container without re-encoding). For example, converting MKV to MP4 when both use H.264 codec is lossless and instant. Star Video Downloader's Convert tab handles this automatically.
Why do YouTube downloads come in WebM or MKV format?
YouTube uses VP9 and AV1 codecs for high-quality streams, which are typically delivered in WebM containers. When Star Video Downloader merges separate video and audio streams, it may produce MKV files. You can convert these to MP4 using the Convert tab.
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