Why is the audio out of sync after converting?

Common causes: (1) variable framerate source rendered as constant (use -vsync vfr to preserve VFR); (2) different audio sample rates not resampled (add -ar 48000 ); (3) container limitations (MP4 with variable framerate misbehaves — prefer MKV during editing, encode to MP4 only at the end). Always run ffprobe on both source and output to compare timing.

Why is the audio out of sync after converting?

Common causes: (1) variable framerate source rendered as constant (use -vsync vfr to preserve VFR); (2) different audio sample rates not resampled (add -ar 48000 ); (3) container limitations (MP4 with variable framerate misbehaves — prefer MKV during editing, encode to MP4 only at the end). Always run ffprobe on both source and output to compare timing.

Guide

VP9 Video Codec: Complete Guide to Google's Open Video Standard

PC By Pablo Cirre • Updated May 7, 2026

What Is VP9?

VP9 is an open-source, royalty-free video compression codec developed by Google and released in 2013. It is the successor to VP8 and was designed to deliver video quality equivalent to HEVC (H.265) while being completely free to use — without patent royalties or licensing fees.

VP9 is the codec behind YouTube's high-quality streaming: since 2013, YouTube has served VP9 to compatible browsers for 720p and above content, representing billions of hours of daily video served in VP9. VP9 achieves approximately 30–40% better compression than H.264 at equivalent quality — a 1080p stream requires 2–3 Mbps in VP9 vs. 4–5 Mbps in H.264.

VP9 Architecture

VP9 is built on the same conceptual framework as H.264 and HEVC — block-based motion compensation plus transform coding — but with key differences:

Superblock Structure

VP9 uses a 64×64 superblock as its basic coding unit (HEVC later adopted this concept at 64×64, AV1 expanded to 128×128). Superblocks are recursively partitioned into coding units of 64×64, 32×32, 16×16, or 8×8 pixels in a quadtree structure.

This flexible block sizing was VP9's major advance over H.264's fixed 16×16 macroblock — allowing efficient coding of both large smooth regions and fine-detail areas.

Prediction

Intra prediction: VP9 has 10 intra prediction modes: DC, True Motion (TM), Vertical, Horizontal, and 6 diagonal/angular directions. Fewer modes than HEVC's 35, but sufficient for most content.

Inter prediction: VP9 uses:

Up to 3 reference frames from the reference frame buffer
Sub-pixel motion compensation with 8-tap interpolation filters (switchable: regular, smooth, sharp)
Motion vector prediction from neighboring blocks
Compound prediction (weighted average of two reference predictions)

Transform Coding

VP9 supports 4×4, 8×8, 16×16, and 32×32 DCT transforms (same as HEVC). An ADST (Asymmetric DCT/DST) is used for intra-coded residuals.

Entropy Coding

VP9 uses a boolean arithmetic coder with probability tables for each syntax element. The probability tables are updated within the frame (adaptive) — VP9 calls this its "context model." This is less efficient than HEVC's CABAC but simpler and faster to decode.

In-Loop Filtering

VP9 has two in-loop filters:

Deblocking filter — reduces blockiness at block boundaries (similar to H.264/HEVC)
Loop restoration filter — VP9 does not have HEVC's SAO filter, but the loop restoration helps reduce ringing artifacts

VP9 Profiles

Profile	Bit depth	Chroma subsampling	Typical use
Profile 0	8-bit	4:2:0	Standard web video
Profile 1	8-bit	4:2:2 or 4:4:4	Professional production
Profile 2	10 or 12-bit	4:2:0	HDR video
Profile 3	10 or 12-bit	4:2:2 or 4:4:4	High-end professional

YouTube uses VP9 Profile 0 for most content, with Profile 2 for HDR streams (YouTube HDR in VP9 uses 10-bit at BT.2020 color space).

VP9 Encoding with libvpx-vp9

FFmpeg's libvpx-vp9 is the primary software VP9 encoder.

# CRF-based encoding (target bitrate=0 forces CRF mode)
ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 33 -b:v 0 output.webm

# Constrained quality (CQ mode — CRF + max bitrate)
ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 33 -b:v 2000k output.webm

# Two-pass for accurate bitrate targeting
ffmpeg -i input.mp4 -c:v libvpx-vp9 -b:v 2000k -pass 1 -f webm /dev/null
ffmpeg -i input.mp4 -c:v libvpx-vp9 -b:v 2000k -pass 2 output.webm

# Good speed/quality balance with row-based multithreading
ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 33 -b:v 0 \
  -row-mt 1 -tile-columns 2 -frame-parallel 0 output.webm

VP9 Quality Scale

VP9 CRF values use a 0–63 scale:

CRF 15-25: Very high quality (transparent)
CRF 30-35: Good quality (recommended default for web)
CRF 40-45: Acceptable quality (small file sizes)
CRF 50+: Low quality

VP9 CRF 33 is roughly comparable to H.264 CRF 23 in visual quality but produces files about 30-40% smaller.

VP9 Speed Preset

The -speed flag (0-8) controls encoding speed:

Speed 0: Best quality, very slow
Speed 1-2: High quality, slow
Speed 4: Default balance
Speed 6-8: Fast, reduced quality

For production encoding: speed 2-4. For real-time: speed 5-7.

WebM: VP9's Container

VP9 is most commonly stored in the WebM container — an open web-friendly container based on Matroska (MKV). WebM supports:

VP8 or VP9 video
Vorbis or Opus audio
VTT (WebVTT) subtitles

WebM files use the .webm extension. They are the native web video format for browsers that support VP9, and are smaller and faster to load than equivalent MP4 files.

VP9 can also be stored in MKV (.mkv) containers for local playback.

Browser and Platform Support

Browser	VP9 support
Chrome	✅ (since 2013)
Firefox	✅ (since 2014)
Edge	✅ (Chromium-based, 2019+)
Opera	✅
Safari	❌ No VP9 support

Safari does not support VP9. This is a significant limitation — all Apple devices (iPhone, iPad, Mac) running Safari cannot play VP9 video. This is the primary reason YouTube still maintains H.264 streams alongside VP9: Safari users need H.264.

When distributing VP9 video for web, always include an H.264 MP4 fallback:

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

VP9 Hardware Support

Device	VP9 decode	Notes
Android (most 2016+)	✅	Nexus/Pixel devices specifically
Chrome OS	✅	Built around Chrome browser
NVIDIA GPU (GTX 950+)	✅	Hardware decode
Intel (6th gen+)	✅	Quick Sync VP9 decode
AMD (RX 400+)	✅	UVD/VCN hardware decode
Apple TV (4th gen+)	✅	Apple added VP9 support
Roku	✅ (some models)

VP9 vs. AV1: The Successor Relationship

VP9 was the stepping stone to AV1. Google contributed VP9's codebase and technical insights to the AOMedia consortium to help develop AV1. As a result:

Feature	VP9	AV1
Royalty-free	✅	✅
Compression efficiency	~30-40% better than H.264	~50-60% better than H.264
Browser support	All except Safari	Chrome, Firefox, Edge, Safari 17+
Hardware decode	Mature	Growing
Encoding speed	Fast (libvpx-vp9 fast mode)	Slow (libaom); Fast (SVT-AV1)

YouTube's trajectory: YouTube began AV1 delivery in 2018 for certain content and has been expanding it since. VP9 remains the workhorse for the majority of YouTube traffic as AV1 hardware decode becomes more widespread.

When to Use VP9 in 2024

Despite AV1 being technically superior, VP9 remains relevant:

YouTube encoding pipeline — YouTube still uses VP9 as the primary codec for most uploaded content
Older AV1 hardware support gap — devices made 2013-2019 may have VP9 hardware decode but not AV1
Faster VP9 software encoding — libvpx-vp9 at speed 5-7 is practical for encoding large video libraries; libaom AV1 is impractically slow for many use cases
Chromebook / Android first — if targeting Chrome/Android users and not needing Safari, VP9 is reliable
WebRTC/video calls — VP9 is widely used in WebRTC implementations (Google Meet, older WebRTC apps)

For new projects in 2024, AV1 via SVT-AV1 is generally the better choice for archival and streaming, but VP9 remains a solid option, especially when targeting Android/Chrome users primarily.

Related conversions

Common video conversions that pair well with this guide:

Frequently Asked Questions

No — Safari has never supported VP9. Apple chose not to implement VP9 support, and since HEVC (H.265) is Apple's preferred high-efficiency codec (with native hardware support on all Apple devices), Apple has little incentive to add VP9. This means VP9 WebM videos will not play in Safari on Mac, iPhone, or iPad. If you publish VP9 video for the web, you must always include an H.264 MP4 fallback using the HTML <video> element with multiple <source> tags. YouTube handles this automatically — it serves VP9 to Chrome/Firefox and H.264 to Safari.

AV1 is the most efficient (royalty-free, ~30% smaller than H.265) but encoding is slow. H.265 (HEVC) saves ~30–50% over H.264 and is supported by every modern phone and desktop. H.264 remains the safest baseline for legacy compatibility. Rule of thumb: archives → AV1, daily use → H.265, broadest reach → H.264.

VP9 provides approximately 30-40% better compression than H.264 — the same video quality at a significantly lower bitrate. A 1080p video that needs 4-5 Mbps in H.264 needs only 2-3 Mbps in VP9. VP9 is also completely royalty-free (no patent fees), while H.264 requires license fees from MPEG-LA for commercial use (though these are minimal for most applications). H.264's major advantage is universal compatibility — it plays on every device and every browser including Safari. VP9 is not supported by Safari, limiting its use for web content where iOS/Mac users are important.

VP9 fornece approximately 30-40% better compressão than H.264 — the same qualidade do vídeo at a significantly baixaer bitrate. A 1080p video that needs 4-5 Mbps in H.264 needs only 2-3 Mbps in VP9. VP9 is also completely royalty-free (no patent fees), while H.264 requires license fees de MPEG-LA para commercial usar (though these are minimal para most aplicativos). H.264's major advantage is universal compatibilidade — it plays on every device e every browser including Safari. VP9 is não suportado by Safari, limiting its usar para web content where iOS/Mac users are important.

VP9 bietet approximately 30-40% better Komprimierung than H.264 — the same Videoqualität at a significantly niedriger Bitrate. A 1080p video that needs 4-5 Mbps in H.264 needs only 2-3 Mbps in VP9. VP9 is also completely royalty-free (no patent fees), while H.264 requires license fees von MPEG-LA für commercial verwenden (though these are minimal für most Anwendungen). H.264's major advantage is universell Kompatibilität — it plays on every device und every browser including Safari. VP9 is nicht unterstützt by Safari, limiting its verwenden für web content where iOS/Mac users are important.

VP9 proporciona approximately 30-40% better compresión than H.264 — the same calidad de vídeo at a significantly bajaer bitrate. A 1080p video that needs 4-5 Mbps in H.264 needs only 2-3 Mbps in VP9. VP9 is also completely royalty-free (no patent fees), while H.264 requires license fees de MPEG-LA para commercial usar (though these are minimal para most aplicaciones). H.264's major advantage is universal compatibilidad — it plays on every device y every browser including Safari. VP9 is no soportado by Safari, limiting its usar para web content where iOS/Mac users are important.

CRF (Constant Rate Factor) is the best default for offline files: ffmpeg picks the bitrate frame-by-frame to maintain perceived quality. Two-pass is only better when you must hit an exact final size (DVD targets). Constant bitrate is for streaming with a fixed channel. For "smallest at quality X" always use CRF.

WebM is an open-source web video container format developed by Google and based on the Matroska (MKV) container standard. WebM files use the .webm extension and are designed specifically for web browser delivery. They support VP8 or VP9 video codecs and Vorbis or Opus audio codecs. WebM was designed to be the native video format for HTML5 video in open browsers (Chrome, Firefox). While technically excellent, WebM's limitation is Safari's lack of VP9 support — Safari cannot play .webm files. For universal web compatibility, combine a .webm source with an .mp4 fallback in an HTML5 <video> element.

WebM is an open-source web video container formato developed by Google e based no Matroska (MKV) container padrão. WebM arquivos usar the .webm extension e are designed specifically para web browser delivery. They support VP8 ou VP9 video codecs e Vorbis ou Opus audio codecs. WebM was designed to be the native video formato para HTML5 video in abrir browsers (Chrome, Firefox). While technically excellent, WebM's limitation is Safari's lack of VP9 support — Safari cannot reproduzir .webm files. para universal web compatibilidade, combine a .webm source com an .mp4 fallback in an HTML5 <video> element.

WebM is an open-source web video Container Format developed by Google und based auf dem Matroska (MKV) Container Standard. WebM Dateien verwenden the .webm extension und are designed specifically für web browser delivery. They support VP8 oder VP9 video Codecs und Vorbis oder Opus audio Codecs. WebM was designed to be the native video Format für HTML5 video in öffnen browsers (Chrome, Firefox). While technically excellent, WebM's limitation is Safari's lack von VP9 support — Safari cannot abspielen .webm files. für universell web Kompatibilität, combine a .webm source mit an .mp4 fallback in an HTML5 <video> element.

WebM is an open-source web video contenedor formato developed by Google y based en el Matroska (MKV) contenedor estándar. WebM archivos usar the .webm extension y are designed specifically para web browser delivery. They support VP8 o VP9 video codecs y Vorbis o Opus audio codecs. WebM was designed to be the native video formato para HTML5 video in abrir browsers (Chrome, Firefox). While technically excellent, WebM's limitation is Safari's lack de VP9 support — Safari cannot reproducir .webm files. para universal web compatibilidad, combine a .webm source con an .mp4 fallback in an HTML5 <video> element.

Common causes: (1) variable framerate source rendered as constant (use <code>-vsync vfr</code> to preserve VFR); (2) different audio sample rates not resampled (add <code>-ar 48000</code>); (3) container limitations (MP4 with variable framerate misbehaves — prefer MKV during editing, encode to MP4 only at the end). Always run <code>ffprobe</code> on both source and output to compare timing.

VP9 remains very relevant in 2024. YouTube still uses VP9 for the majority of its video streams (AV1 adoption is expanding but not yet dominant). VP9 is practically universal among non-Apple browsers and Android devices, and VP9 hardware decode support is mature and widespread (devices since 2015-2016). AV1 software encoding (libaom) is still extremely slow for many use cases, making VP9 more practical for encoding large video libraries quickly. The key advantage of AV1 is 30% better compression than VP9, making it worth the encoding time for content that will be served millions of times (like YouTube). For smaller-scale operations, VP9 remains an excellent royalty-free choice.

Yes if you only change the container: <code>ffmpeg -i in.mkv -c copy out.mp4</code>. This remuxes the stream without re-encoding, takes seconds even for hours of footage. Limitations: codec must be supported by the target container (e.g. you cannot put H.264 in WebM, only VP8/VP9/AV1). To shrink size you must re-encode.