Why Format Choice Actually Matters

Format choice is not a cosmetic decision. The wrong format for the wrong situation creates real problems: files that won't open on certain devices, quality loss during unnecessary conversion steps, file sizes that are 8x larger than they need to be, and videos that get rejected by upload platforms.

Here are the situations where picking the wrong format actually costs you something:

  • You download a WebM clip to share via iMessage on an iPhone. iMessage does not support WebM. The recipient cannot open it. You have to convert it, which takes extra time and potentially degrades quality.
  • You download an MKV to post on TikTok. TikTok does not accept MKV. You discover this after the upload fails at 98% progress.
  • You download a WAV audio file for podcast listening on your phone. It's 1.8 GB for a 3-hour episode. Your phone almost runs out of storage.
  • You download a 128kbps MP3 of a music track you plan to use in a video production. Every time you re-encode it, quality degrades further. You end up with noticeably compressed audio in the final video because you started with compressed audio.
  • You download MP4 when you specifically needed WebM for a web project, and now every browser is sending a 4x-larger file to visitors than necessary.

None of these are catastrophic. All of them are avoidable if you spend two minutes understanding the format you're choosing.

Containers vs Codecs: The Key Concept

Before getting into specific formats, there is one concept that makes everything else make sense. It takes 30 seconds to understand and it explains about 80% of the confusion people have about video formats.

The container is the box

MP4, WebM, MKV, AVI, MOV. These are all container formats. A container is like a box that holds different things: video data, audio data, subtitle tracks, chapter information, thumbnail images. The container defines how all these different streams are organized and stored together in one file.

The container does not determine quality directly. It does not determine how the video was compressed. It is organizational structure.

The codec is what's inside

H.264, H.265, VP9, AV1, Opus, AAC, MP3. These are codecs. A codec (compressor-decompressor) is the algorithm that actually compresses and decompresses the video or audio data. The codec determines quality, file size, and compatibility in a fundamental way.

The same video content encoded with H.264 at a given bitrate will look different from the same content encoded with H.265 at the same bitrate, because the codecs have different compression efficiency.

How they work together

When you have an MP4 file, that means: the container is MPEG-4 Part 14 (MP4). The video stream inside is almost certainly H.264, though it could be H.265 (HEVC). The audio stream inside is almost certainly AAC.

When you have a WebM file: the container is WebM. The video stream inside is VP9 (or the newer AV1). The audio stream is Opus.

When you have an MKV file: the container is Matroska. The video inside could be H.264, H.265, VP9, AV1, or even something unusual like AVC or HEVC. MKV is specifically designed to hold almost any codec.

This container-codec relationship is why you sometimes have two files with the same apparent quality but different file sizes. They may contain the same video content but encoded with different codecs at different efficiency levels.

Tip: If you want to check what codec is actually inside a file, download the free tool MediaInfo. It shows you the exact container, video codec, audio codec, bitrate, resolution, and frame rate of any media file in seconds.

MP4 Explained

MP4 is the default. When in doubt, choose MP4. That is the conclusion. Here is why.

What it is

MP4 stands for MPEG-4 Part 14. It is a container format standardized in 2001 and has been universally supported on every platform, operating system, device, and application for well over a decade. The video codec inside is almost always H.264 (also called AVC, Advanced Video Coding), which was standardized in 2003 and remains the most widely supported video codec on Earth in 2026.

Where MP4 works

Every smartphone. Every tablet. Every smart TV. Every streaming platform. Every social media platform (TikTok, Instagram, YouTube, Twitter/X, Facebook, LinkedIn). Every video editing application. Every browser. Windows Media Player. QuickTime. VLC. Your car's USB port. Your 10-year-old camera. Your grandmother's DVD player (if it has a USB slot). Your Raspberry Pi. Your work laptop with its IT-locked-down software environment.

MP4 with H.264 video works everywhere. This is not a slight exaggeration for emphasis. It is genuinely the most universally compatible video format that exists.

Quality and file size

H.264 is not the most efficient codec available. H.265 produces the same visual quality at roughly half the file size. VP9 and AV1 are similarly more efficient. But H.264's compatibility advantage outweighs its efficiency disadvantage for most use cases.

A typical 1080p30 H.264 MP4 clip runs at 4-8 Mbps (megabits per second). A 10-minute clip at 6 Mbps is roughly 450 MB. That's not small, but it's manageable. For comparison, lossless video at 1080p30 would be 5-10 GB for the same duration.

When to choose MP4

Choose MP4 when: you don't know exactly where the file will be used. You're sharing with other people who may have varying setups. You're posting to social media. You're sending it via email or messaging app. You're putting it in a presentation. You're uploading it to any platform for any purpose. This covers probably 90% of all use cases.

When MP4 is not the right choice

MP4 is not the right choice when: you need the smallest possible file size for web delivery (use WebM). You need to store multiple audio tracks or subtitle streams in one file (use MKV). You need audio only (use MP3 or M4A). You need lossless audio (use WAV).

WebM Explained

WebM is what Google built for the web. It's great for web use. Less great for everything else.

What it is

WebM is an open, royalty-free container format developed by Google and released in 2010. It was designed specifically for web delivery of video. The video codec inside is VP9 (sometimes AV1 in newer encodes). The audio codec is Opus. Both VP9 and Opus are open-source, royalty-free, and designed by Google/the Xiph foundation.

The efficiency advantage

VP9 is roughly 40-50% more efficient than H.264 at comparable visual quality. That means a WebM file and an MP4 file of the same video at the same perceived quality will see the WebM file come in at roughly half the size. For web delivery, where bandwidth translates directly to hosting costs and page load speed, that 50% reduction is significant.

AV1 (the successor to VP9, also used in WebM) pushes this further, being 30-50% more efficient than VP9. YouTube itself uses AV1 for 4K playback and is expanding AV1 usage across more content. Discord serves video messages in WebM with VP9/AV1. Major streaming platforms have been adopting AV1 for high-efficiency delivery.

Compatibility reality

Here is the trade-off. WebM is not supported on iOS before iOS 14.5. It is not supported by default in some older Windows applications. It is not accepted by TikTok or Instagram for upload. It is not compatible with many car stereo USB systems. It does not play in Windows Media Player without additional codecs. And many people have simply never heard of it, so sharing a WebM file with a non-technical person is a recipe for "this file won't open" messages.

In a browser, WebM is great. Chrome, Firefox, Edge, and Safari (recent versions) all support it natively. If you are embedding video on a website, WebM is an excellent choice for smaller file sizes. If you are sharing a clip with other humans, use MP4.

When to choose WebM

Choose WebM when: you're embedding video in a web page and want smaller file sizes. You're posting to Discord (which handles WebM well). You're delivering to an audience you know will be watching in a modern browser. File size is a meaningful constraint.

MKV Explained

MKV is the format for people who keep things. It's the archiver's format. It holds everything.

What it is

MKV stands for Matroska Video. Matroska is an open-source multimedia container project, and MKV is its video container format (there is also MKA for audio-only). The Matroska project was founded in 2002 with the explicit goal of creating an open container format that could hold virtually any combination of video, audio, and metadata streams.

The key word is "virtually any." MKV can hold H.264 video, H.265 video, VP9, AV1, or practically any other video codec. It can hold AAC audio, Opus audio, FLAC audio, DTS, Dolby TrueHD, or practically any audio codec. It can hold multiple audio tracks in different languages simultaneously. It can hold subtitle tracks in multiple languages. It can hold chapter markers. It can hold embedded thumbnail art. It can hold attached files.

The multiple-track capability

This is MKV's defining feature. Imagine a film that has English dialogue, French dubbed audio, Spanish dubbed audio, English subtitles for the deaf, French subtitles, and chapter markers for each scene. All of that in a single MKV file. Switch between audio tracks and subtitle tracks in your media player without managing multiple files. VLC, Kodi, Plex, and MPC-HC all handle this gracefully.

This is why MKV is the dominant format for archived films and television episodes in the media enthusiast community. The content, all available audio tracks, and all subtitle options travel together in one file.

Compatibility limitations

MKV's flexibility is also its compatibility liability. Because it can contain so many different codecs, older or simpler playback devices don't always know what to do with it. Smart TVs pre-2018 often cannot play MKV files with H.265 video. iOS and macOS cannot open MKV files without VLC or another third-party player (QuickTime does not support MKV natively). Streaming and social platforms universally reject MKV uploads. Windows can play MKV in Windows 10 and later through the built-in Media Player, but older Windows versions need VLC.

When to choose MKV

Choose MKV when: you are archiving video content with multiple audio or subtitle tracks. You want a container that future-proofs your files (MKV can hold any codec that gets invented later). You are using Plex, Kodi, or Jellyfin as your media server (they handle MKV excellently). You know you will only be playing the file yourself on a capable device, not sharing it.

Do not choose MKV when you need to share the file with other people, post it to a platform, or use it anywhere outside your own media setup.

MP3 Explained

MP3 is 33 years old and it still runs the world of portable audio. That's not an accident.

What it is

MP3 stands for MPEG-1 Audio Layer 3. It was standardized in 1993 by the Fraunhofer Society and became the format that made digital music distribution practical in the era of slow internet connections and limited hard drive space. The last relevant MP3 patents expired in 2017, making it fully free and open to implement without royalties.

MP3 works by discarding audio information that psychoacoustic research suggests is least perceptible to human hearing. Sounds masked by louder simultaneous sounds are removed. Very high-frequency content (above what most adults can hear distinctly) is compressed aggressively. The result is a file roughly 7-10x smaller than lossless audio while sounding nearly identical under normal listening conditions.

Bitrate is everything with MP3

The quality of an MP3 is almost entirely determined by its bitrate, measured in kilobits per second (kbps). Here is the practical breakdown:

  • 64kbps: Clearly degraded. Acceptable for voice-only content where quality doesn't matter. FM radio sounded better than this.
  • 96kbps: Better. Still audibly compressed on music with complex high-frequency content. Suitable for spoken-word content.
  • 128kbps: The historical "web standard" for music. Acceptable for casual listening, notably compressed to trained ears on complex music.
  • 160kbps: Good quality. Compression artifacts difficult to detect for most listeners on most content.
  • 192kbps: Near-transparent for most content on most playback systems. This is the recommended bitrate for general-purpose music downloads.
  • 256kbps: High quality. Indistinguishable from 320kbps for virtually all listeners in any practical setting.
  • 320kbps: Maximum standard MP3 bitrate. Highest quality possible in the MP3 format. Files are meaningfully larger than 192kbps with no perceptible benefit for typical listening.

Universal compatibility

Every audio player on Earth plays MP3. Car stereos. Bluetooth speakers. Headphones with onboard storage. Smartwatches. Amazon Echo. Google Home. MP3 players from 2005 that still work. Every streaming platform can transcode MP3. Every podcast app handles MP3. Every email client can preview or attach MP3. This compatibility is the reason MP3 remains the default sharing format for audio in 2026 even though better-sounding formats exist.

When to choose MP3

Choose MP3 when: you want audio that works everywhere without exception. You are making a podcast. You are sharing a voice memo. You are saving lecture audio for listening on the go. You want audio for a car trip. Basically: audio you plan to listen to, on any device, in any context, with any other person who might also want to listen to it.

M4A and AAC Explained

M4A is the technically superior version of MP3. The problem is that "technically superior" doesn't count for much when the old format works on everything.

What it is

M4A is a container format (specifically MPEG-4 Part 14, the same base as MP4) that contains AAC (Advanced Audio Coding) audio. AAC was standardized in 1997 as the designated successor to MP3, developed by a consortium including Fraunhofer, Dolby, AT&T, Sony, and Nokia. Apple adopted AAC as the default format for iTunes in 2003, which is largely why it spread so widely.

The quality advantage over MP3

AAC is genuinely more efficient than MP3 at the same bitrate. The psychoacoustic model AAC uses is more sophisticated. The practical result: 128kbps AAC sounds roughly equivalent to 160-192kbps MP3. This means that if you want a file that sounds like a 192kbps MP3 but you want it to be smaller, 128kbps M4A is approximately equivalent.

YouTube's native audio format is typically 128kbps AAC or 160kbps Opus, which is why YouTube audio sounds surprisingly good relative to what you'd expect from those bitrate numbers.

Compatibility

M4A compatibility is very good in 2026 but not perfect. All Apple devices (iPhone, iPad, Mac) support M4A natively. All modern Android phones support M4A. Windows 10 and later support M4A natively. Most car stereos made after 2015 support M4A. Modern Bluetooth speakers generally support M4A.

Where it can fail: very old devices, cheap generic MP3 players, some older car stereos, and some specialized audio equipment that explicitly lists "MP3" support but not "AAC." For sharing with unknown recipients on unknown devices, MP3 is safer. For your own personal use on modern devices, M4A at 128kbps sounds better than MP3 at 128kbps and is the same file size.

When to choose M4A

Choose M4A when: you want better audio quality than MP3 at the same file size, and you know the playback device supports AAC (essentially any device made after 2012). You're on Apple hardware primarily. You're storing a large library of audio and want to save space without sacrificing quality. The file is for personal use rather than wide distribution.

WAV Explained

WAV is not for listening. It is for working.

What it is

WAV (Waveform Audio File Format) was developed by Microsoft and IBM and introduced in 1991. It stores audio as uncompressed PCM (Pulse Code Modulation) data. PCM is the same format used on audio CDs (16-bit, 44.1kHz stereo). No codec. No compression. Every sample of audio is stored exactly as it was captured.

The result is perfect, lossless audio fidelity and enormous files. One minute of CD-quality stereo WAV audio is 10.5 MB. One minute of 192kbps MP3 is 1.4 MB. WAV is 7.5x larger for the same content at CD quality. At 24-bit/96kHz (the format used in audio production), one minute of WAV is 34 MB.

Why production audio needs WAV

Every time you apply a lossy compression step to audio, you permanently discard information. When you edit audio in a DAW (Digital Audio Workstation), you are making calculations on every sample. If you start with a 128kbps MP3 and apply EQ, compression, reverb, and other effects, then export to MP3 again, the codec has to re-compress audio that was already compressed. Each re-compression step introduces additional artifacts. Over multiple rounds of editing and exporting, these artifacts compound.

WAV eliminates this problem. You work with perfect source audio. Every calculation is performed on the complete sample data. When you finally export the finished product, you compress once, from WAV to MP3 or M4A, and the compression artifacts appear only in that final step rather than accumulating across multiple generations.

This is why recording studios, podcast production workflows, film audio post-production, and music production all use lossless formats internally. The WAV goes through the entire editing process and MP3 is produced only at the distribution stage.

WAV compatibility

WAV is universally supported on computers and professional audio equipment. It is less universally supported on portable devices and cheap consumer electronics (which often only support MP3 and sometimes AAC). Most modern smartphones can play WAV. Cars vary. Specialized audio production equipment definitely plays WAV. Consumer devices are less certain.

When to choose WAV

Choose WAV when: you are going to edit the audio in any audio software (Audacity, GarageBand, Logic, Pro Tools, Adobe Audition, DaVinci Resolve's Fairlight). You are using the audio as a sample in a music production. You need to apply audio effects, EQ, or processing to the file. You are delivering audio to a professional audio facility. You are archiving a recording of significant personal or historical importance and want absolutely no quality loss. You need to sync audio to video precisely in post-production.

Do not choose WAV for listening. The file size cost is enormous and the quality benefit is imperceptible compared to 192kbps MP3 on any consumer playback device.

Full Comparison Table

Format Type Codec(s) Typical file size (10 min, 1080p) Compatibility Quality Best use case
MP4 Video H.264 + AAC 450-900 MB Universal Very good Everything, everywhere
WebM Video VP9/AV1 + Opus 200-500 MB Good (browsers, Discord) Excellent (more efficient) Web embedding, smaller files
MKV Video Any (flexible) Varies by codec Good (VLC, Plex, Kodi) Depends on codec inside Archiving with multiple tracks
MP3 Audio only MP3 ~14 MB (192kbps) Universal Good (192kbps+) Audio for any device, sharing
M4A Audio only AAC ~9 MB (128kbps) Very good (modern devices) Better than MP3 at same bitrate Personal audio library, Apple devices
WAV Audio only PCM (none) ~105 MB (10 min stereo) Good (computers, pro equipment) Lossless (perfect) Audio editing, production, sampling

How to Choose the Right Format

Here is the decision process in plain text, not a flowchart because flowcharts are hard to read on mobile.

Step 1: Video or audio only?

Do you need the video (moving images) or just the audio (sound)? If you only care about what's being said and don't need the video, choose MP3 (universal) or M4A (better quality). This saves a significant amount of file size. A 10-minute clip is 450-900 MB as MP4 video but only 9-14 MB as audio. If you need the visual content, continue to step 2.

Step 2: Do you know where the file will be used?

If you don't know yet, or if you'll be sharing it with other people, choose MP4. Full stop. It will work everywhere. When in doubt, MP4.

If you do know the specific destination, continue to the relevant option:

  • Posting to TikTok, Instagram Reels, YouTube Shorts, Facebook, Twitter/X, LinkedIn: MP4. These platforms all accept MP4 and may not accept others.
  • Embedding on a website you control: WebM for smaller file size and faster loading. Optionally serve MP4 as a fallback for older browsers using the HTML video element with multiple source tags.
  • Archiving for long-term personal storage with multiple audio tracks or subtitles: MKV.
  • Sending via Discord: WebM or MP4. Discord handles both well. WebM is smaller.
  • Editing in video software (Premiere, DaVinci Resolve, Final Cut): MP4 for maximum compatibility with all editors. MKV works in many but not all editors.
  • Sending to someone who definitely has a Mac or iPhone: MP4 still works fine and is the safer choice over WebM.

Step 3: For audio, what's the playback device?

Modern device (any smartphone post-2012, modern computer, modern car): M4A at 128kbps gives better quality than MP3 at 128kbps at the same file size. Use M4A.

Unknown device, old device, wide distribution, car stereo of uncertain vintage: MP3 at 192kbps. Works everywhere.

Audio production, editing, mixing, sampling: WAV. No exceptions.

Technical Details for Nerds

If you got this far and want to go deeper, here is the technical layer that underpins everything above.

How video codecs measure quality: CRF and bitrate

Video codecs use two primary modes for controlling quality:

Constant Bitrate (CBR): The encoder uses exactly the specified number of bits per second, regardless of whether the content is complex or simple. Simple content (a static background) gets the same bits as complex content (fast motion, lots of detail). This wastes bits on simple sections and starves complex sections. CBR is used for streaming scenarios where buffer management requires predictable file sizes.

Constant Rate Factor (CRF) or Variable Bitrate (VBR): The encoder allocates more bits to complex frames and fewer bits to simple frames, targeting a consistent perceived quality level rather than a consistent file size. This is almost always the right choice for non-streaming use. Lower CRF values mean higher quality (and larger files). In ffmpeg:

# H.264, CRF 18 = very high quality (visually lossless for most content)
ffmpeg -i input.mp4 -c:v libx264 -crf 18 output.mp4

# H.264, CRF 23 = default quality (good balance)
ffmpeg -i input.mp4 -c:v libx264 -crf 23 output.mp4

# H.264, CRF 28 = lower quality, smaller file
ffmpeg -i input.mp4 -c:v libx264 -crf 28 output.mp4

# VP9 (WebM), CRF 31 = similar quality to H.264 CRF 23 at ~50% smaller file
ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 31 -b:v 0 output.webm

Codec efficiency comparison

At the same perceived visual quality, the approximate file size ratios between codecs are:

  • H.264: Baseline. 100% file size.
  • H.265 (HEVC): ~50% of H.264 file size at equivalent quality. Slower to encode, hardware decoding support required for mobile.
  • VP9: ~55-60% of H.264 file size. Open source, royalty-free, used by YouTube for most HD content.
  • AV1: ~40-50% of H.264 file size. The newest of these codecs, royalty-free, very slow to encode in software but increasingly hardware-accelerated. Netflix, YouTube, and most major streaming platforms are deploying AV1 aggressively.

The chroma subsampling detail

Most video you download uses 4:2:0 chroma subsampling. This means color information is stored at half the horizontal and vertical resolution of the luma (brightness) information. Human vision is more sensitive to brightness differences than color differences, so this trade-off is largely invisible in normal viewing. Professional production workflows use 4:2:2 or 4:4:4 subsampling to preserve full color detail for color grading. YouTube's output is always 4:2:0, so any video you download from YouTube is already at 4:2:0 regardless of which format you choose.

Audio codec efficiency

In terms of bits required to achieve transparent (indistinguishable from lossless) quality:

  • MP3: ~192-256 kbps for transparent quality in most double-blind tests
  • AAC: ~128-160 kbps for comparable transparency
  • Opus: ~96-128 kbps for comparable transparency (Opus is remarkably efficient, especially at lower bitrates)
  • FLAC (lossless): ~700-1400 kbps (lossless, so quality is definitionally perfect)
  • WAV/PCM: ~1411 kbps for 16-bit/44.1kHz stereo (completely uncompressed)

Opus is objectively the most efficient audio codec in common use. It was developed by Xiph.Org and is used by WhatsApp, Discord, WebRTC video calls, Zoom, and YouTube's highest-quality audio streams. The reason it hasn't replaced MP3 entirely is compatibility: many older devices and applications don't support Opus. But for anything delivered over the web or within modern applications, Opus at 96kbps sounds better than MP3 at 192kbps.

How YouTube encodes the videos you download

When you upload a video to YouTube, YouTube re-encodes it into multiple formats for different devices and connection speeds. The streams they typically make available (as of 2026) are:

  • VP9 video at multiple resolutions from 144p to 4K (or 8K for eligible content)
  • AV1 video for 4K and some lower resolutions
  • H.264 video for compatibility fallback
  • Opus audio at 160kbps
  • AAC audio at 128kbps (for M4A container)

When you download via YTCut or yt-dlp, the tool fetches these pre-encoded streams from YouTube's servers and either passes them through as-is or re-encodes them into your requested format. If you request MP4 and the native stream is VP9/Opus, the tool will re-encode to H.264/AAC. If you request WebM and the native stream is already VP9/Opus, it can just repackage it into a WebM container without re-encoding, preserving the original quality.

FAQ

Can I convert between formats without losing quality?

Converting between lossless formats (WAV to FLAC, for example) can be done without any quality loss. Converting from a lossless format to a lossy format (WAV to MP3) involves intentional quality reduction by the codec, but you control how much through the bitrate setting. Converting between two lossy formats (MP3 to M4A, WebM to MP4) always involves a quality penalty because you're re-encoding already-compressed audio. The result will sound like the lower of the two bitrates, not the higher. Avoid this whenever possible: keep your working files in a lossless format and only compress to lossy at the final export stage.

Why does the same video look different in MP4 vs WebM even at the "same quality"?

Because the quality settings don't directly translate between codecs. H.264 CRF 23 is not the same visual quality as VP9 CRF 23. Each codec has its own quality scale. What "looks the same" depends on finding the CRF values for each codec that produce equivalent VMAF (Video Multimethod Assessment Fusion) scores, which is the standard perceptual quality metric. For general guidance: H.264 CRF 23 is roughly equivalent to VP9 CRF 31 in perceived quality at significantly smaller file size for VP9.

Does resolution (1080p vs 4K) affect which format I should choose?

Resolution affects file size but not format choice. A 4K MP4 is better than a 4K WebM only in terms of compatibility, exactly as a 1080p MP4 compares to a 1080p WebM. For 4K specifically, H.265 and AV1 are much more commonly used than H.264 because H.264's efficiency makes 4K H.264 files impractically large. A 10-minute 4K60fps H.264 clip can exceed 10 GB. The same content in H.265 is around 4-5 GB. In AV1, around 2-3 GB. Format choice matters more at higher resolutions because the file size differences are larger in absolute terms.

What's the difference between H.264 and H.265?

H.265 (also called HEVC, High Efficiency Video Coding) is the successor to H.264, standardized in 2013. At the same visual quality, H.265 produces files roughly 40-50% smaller than H.264. The trade-offs: H.265 is more computationally expensive to encode (slower), hardware decoders for H.265 are required for smooth mobile playback (all phones since ~2016 have hardware H.265 decoders), and for a long time H.265 had patent licensing complications. Compatibility is very good in 2026 for modern devices. Some older smart TVs, older Blu-ray players, and legacy software still cannot play H.265. MP4 files can contain either H.264 or H.265 video.

Is AV1 ready for everyday use in 2026?

Mostly yes. AV1 is supported natively in Chrome, Firefox, Edge, and recent Safari versions. Android has supported AV1 hardware decoding since the Snapdragon 888 generation (2020). Apple added AV1 hardware decoding in the A17 Bionic chip (iPhone 15 Pro) and M3 Macs. YouTube uses AV1 for 4K playback on supported devices. The remaining gaps are: older iPhones (pre-A17) decode AV1 in software which is slow, some older Android devices lack hardware decode, and some Windows applications haven't added AV1 support yet. For web embedding targeting modern browsers, AV1 in WebM is viable. For wide distribution, MP4 with H.264 is still safer.

Why does VLC play everything?

Because VLC ships with its own built-in implementations of virtually every video and audio codec ever standardized, including many obscure and legacy codecs. VLC does not rely on the operating system's codec library. It is entirely self-contained. This is why VLC plays MKV files with FLAC audio on a fresh Windows installation that has none of those codecs installed: VLC brought its own. This design choice made VLC indispensable as a universal media player for over two decades. It also means that if a file plays in VLC but not in another application, the other application is missing codec support that VLC has.