How to Convert WebM to MP4: Quick Browser-Friendly Guide

What Is WebM and Why Would You Need to Convert It?

WebM is an open-source video format developed by Google in 2010. It was created as a royalty-free alternative to MP4 for web video. WebM files typically contain VP8 or VP9 video with Vorbis or Opus audio, all wrapped in a Matroska-based container.

While WebM is great for web embedding (it is natively supported by Chrome, Firefox, and Edge), it has significant compatibility gaps. Apple devices, many smart TVs, and most video editing software do not support WebM natively. If you have downloaded a video from the web, received a WebM screen recording, or exported from a browser-based tool, you will likely need to convert it to MP4 for broader use.

This guide covers every method for converting WebM to MP4, from one-click online tools to fine-tuned FFmpeg commands.

WebM vs. MP4: Browser and Device Support

The pattern is clear: MP4 with H.264 is the only format with truly universal support. WebM works well within web browsers (except Safari) but struggles everywhere else.

<video>
  <source src="video.webm" type="video/webm" />
  <source src="video.mp4" type="video/mp4" />
</video>

Where Do WebM Files Come From?

Before diving into conversion methods, it helps to understand why you might have WebM files in the first place:

• Web downloads: Many websites serve video in WebM format, and browser "Save Video" functionality downloads the WebM version
• Screen recordings: Browser-based screen recorders (like the one built into Chrome) often export as WebM
• YouTube downloads: Third-party tools sometimes download the VP9/WebM stream from YouTube
• Web applications: Online video editors and social tools may export in WebM
• Linux screen capture: Tools like OBS on Linux default to WebM in some configurations
• Google services: Google Meet recordings and some Drive-hosted videos use WebM

Method 1: Convert WebM to MP4 Online

The fastest path from WebM to MP4 is the MP4 Converter. Upload your WebM file, and the converter handles all the technical details automatically.

Steps

1. Open the MP4 Converter
2. Upload your WebM file (drag and drop or click to browse)
3. Select your preferred quality level
4. Click Convert
5. Download the MP4 file

The online tool automatically detects the VP8/VP9 video and Vorbis/Opus audio in your WebM file and converts them to H.264 and AAC for maximum MP4 compatibility.

For additional format options or to convert WebM to other video formats, use the full Video Converter.

Method 2: FFmpeg Conversion

FFmpeg gives you complete control over the conversion process. Here are commands for every common scenario.

Standard Conversion (High Quality)

ffmpeg -i input.webm -c:v libx264 -crf 20 -preset slow \
  -c:a aac -b:a 192k -movflags +faststart output.mp4

Quick Conversion (Faster Processing)

ffmpeg -i input.webm -c:v libx264 -crf 23 -preset fast \
  -c:a aac -b:a 128k output.mp4

Maximum Quality (Minimal Loss)

ffmpeg -i input.webm -c:v libx264 -crf 16 -preset veryslow \
  -c:a aac -b:a 320k -movflags +faststart output.mp4

Convert to H.265 (Smaller File)

For better compression, especially with high-resolution WebM files:

ffmpeg -i input.webm -c:v libx265 -crf 24 -preset slow \
  -c:a aac -b:a 192k -movflags +faststart output.mp4

Two-Pass Encoding (Best Quality per Bitrate)

For professional results where you need a specific target file size:

# Pass 1
ffmpeg -i input.webm -c:v libx264 -b:v 5M -preset slow \
  -pass 1 -an -f null /dev/null

# Pass 2
ffmpeg -i input.webm -c:v libx264 -b:v 5M -preset slow \
  -pass 2 -c:a aac -b:a 192k output.mp4

Method 3: Can You Remux WebM to MP4?

Unlike MKV to MP4 conversion, remuxing WebM to MP4 is generally not practical. Here is why:

WebM uses VP8/VP9 video and Vorbis/Opus audio. While the MP4 container technically supports VP9 (it is allowed by the ISO standard), very few players, devices, or platforms handle VP9 inside MP4 correctly. Vorbis and Opus are not supported in MP4 at all.

# This technically works but produces a file most players can't handle
ffmpeg -i input.webm -c copy output.mp4
# WARNING: Most players will not play VP9 video in an MP4 container

The one exception: if you are converting from WebM to MKV, remuxing works perfectly since MKV supports all codecs. But for MP4, re-encoding is the reliable path.

Handling Common WebM Sources

Screen Recordings from Chrome

Chrome's built-in screen recorder and many web-based recording tools produce WebM with VP8/VP9 video. These are typically at screen resolution (1080p or 1440p) with relatively low motion:

ffmpeg -i screen_recording.webm -c:v libx264 -crf 22 -preset medium \
  -c:a aac -b:a 128k -movflags +faststart screen_recording.mp4

Screen recordings compress very well because they have large static areas. CRF 22-25 produces excellent results at small file sizes.

YouTube Downloads (VP9)

Videos downloaded from YouTube in VP9/WebM format are already heavily compressed. Re-encoding adds another round of compression, so use a low CRF to preserve quality:

ffmpeg -i youtube_video.webm -c:v libx264 -crf 18 -preset slow \
  -c:a aac -b:a 192k -movflags +faststart youtube_video.mp4

High-Resolution WebM (4K)

For 4K WebM files, H.265 encoding is recommended to keep file sizes manageable:

ffmpeg -i input_4k.webm -c:v libx265 -crf 22 -preset slow \
  -c:a aac -b:a 256k -movflags +faststart output_4k.mp4

For comprehensive 4K conversion guidance, see our 4K video conversion guide.

Converting WebM Audio

Some WebM files are audio-only (commonly used for podcasts, music, and web audio). These contain Opus or Vorbis audio without a video stream.

WebM to MP3

ffmpeg -i audio.webm -c:a libmp3lame -b:a 320k output.mp3

WebM to AAC

ffmpeg -i audio.webm -c:a aac -b:a 256k output.m4a

WebM to WAV (Lossless)

ffmpeg -i audio.webm -c:a pcm_s16le output.wav

For more audio conversion options, use the Audio Converter or read about how to convert MP4 to MP3.

Batch Converting WebM Files

Shell Script for Bulk Conversion

#!/bin/bash
mkdir -p converted

for file in *.webm; do
  [ -f "$file" ] || continue
  output="converted/${file%.webm}.mp4"
  echo "Converting: $file"
  ffmpeg -i "$file" -c:v libx264 -crf 20 -preset medium \
    -c:a aac -b:a 192k -movflags +faststart "$output" -y
  echo "Done: $output"
done

echo "All WebM files converted to MP4!"

Parallel Batch Conversion

For faster processing of many files, use GNU Parallel or xargs:

# Convert 4 files at a time using xargs
ls *.webm | xargs -P 4 -I {} bash -c \
  'ffmpeg -i "{}" -c:v libx264 -crf 20 -preset fast \
   -c:a aac -b:a 192k "converted/${1%.webm}.mp4" -y' _ {}

For more batch processing techniques, check our batch processing guide.

Quality Comparison: VP9 vs. H.264 at the Same Bitrate

When converting from VP9 to H.264, understanding the efficiency difference helps set expectations:

VMAF (Video Multi-Method Assessment Fusion) scores range from 0-100, where 100 is perfect quality. At lower bitrates, VP9 has a clear advantage. At higher bitrates, the codecs converge. When converting, using CRF mode (rather than a fixed bitrate) lets the encoder use whatever bitrate is needed to maintain quality, making the codec efficiency difference less relevant.

For a deep dive into codec comparison, read H.265 vs H.264 vs AV1.

Converting MP4 to WebM

While this guide focuses on WebM to MP4, you may occasionally need the reverse direction — for example, to optimize video for web delivery.

MP4 to WebM (VP9)

ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 30 -b:v 0 \
  -row-mt 1 -c:a libopus -b:a 128k output.webm

MP4 to WebM (VP8, for older browser support)

ffmpeg -i input.mp4 -c:v libvpx -crf 10 -b:v 1M \
  -c:a libvorbis -b:a 128k output.webm

To learn more about web-optimized formats, check our guide on what is WebP format (the image equivalent of WebM).

Troubleshooting

Conversion Is Very Slow

VP9 decoding is more CPU-intensive than H.264 decoding. If conversion is too slow:

1. Use a faster preset (-preset fast or -preset veryfast)
2. Use hardware-accelerated decoding if available
3. Use the online Video Converter to offload processing to cloud servers

Audio Missing After Conversion

Some WebM files have audio in Opus format at unusual sample rates. Force the output sample rate:

ffmpeg -i input.webm -c:v libx264 -crf 20 \
  -c:a aac -b:a 192k -ar 48000 output.mp4

Output Has Green/Purple Artifacts

This usually indicates a color space issue with VP9 content. Add explicit pixel format conversion:

ffmpeg -i input.webm -c:v libx264 -crf 20 \
  -pix_fmt yuv420p -c:a aac -b:a 192k output.mp4

File Will Not Play on iPhone

iPhones require H.264 Baseline or Main profile for older models, or High profile for newer ones. Force compatibility:

ffmpeg -i input.webm -c:v libx264 -crf 20 -profile:v high -level 4.1 \
  -pix_fmt yuv420p -c:a aac -b:a 192k -movflags +faststart output.mp4

When to Use WebM Instead of MP4

Despite MP4's broader compatibility, there are situations where WebM is the better choice:

• Web-only distribution where Safari support is not critical
• Open-source projects that prefer royalty-free formats
• Cost-sensitive streaming where VP9's compression advantage reduces bandwidth bills
• Google ecosystem (YouTube, Google Drive, Chrome) where WebM is a first-class citizen

For most other scenarios — email attachments, social media uploads, device playback, and editing workflows — MP4 is the safer choice. Learn more about format selection in our best video formats guide.

Frequently Asked Questions

Is WebM better quality than MP4?

Not inherently. Quality depends on the codec and settings, not the container. VP9 (in WebM) is slightly more efficient than H.264 (in MP4) at the same bitrate, but H.265 (also in MP4) matches or exceeds VP9 efficiency.

Can I play WebM on iPhone?

Not natively. Safari and iOS do not support VP8/VP9 video. You need to convert to MP4 first using the MP4 Converter or the methods described in this guide.

Does converting WebM to MP4 lose quality?

Yes, re-encoding always introduces some quality change. However, with appropriate CRF settings (18-20 for H.264), the loss is imperceptible. Use a lower CRF value if quality preservation is critical.

Why are my WebM files so small compared to MP4?

VP9 (the codec typically used in WebM) is more efficient than H.264, so it produces smaller files at the same quality. When converting to H.264, expect files to grow 20-40%. Use H.265 as the target codec to maintain similar file sizes.

Conclusion

Converting WebM to MP4 is a straightforward process that dramatically improves your video's compatibility across devices and platforms. While remuxing is not practical due to codec incompatibilities, re-encoding with proper quality settings produces excellent results.

For quick conversions, use the MP4 Converter online. For batch processing or advanced workflows, FFmpeg gives you full control. Choose CRF 18-20 for high quality, and consider H.265 as the target codec if you want to keep file sizes similar to the original WebM.

Explore more conversion guides: how to convert MOV to MP4, how to convert MKV to MP4, and how to convert AVI to MP4. For all your video format needs, the Video Converter handles dozens of formats in a single tool.