What Happens When You Convert Video
We converted one real video to 31 formats and measured the actual file size and picture quality of each. No spec-sheet guesses, just tested results.
Most format charts tell you what a codec can do in theory. This one shows what actually happens when you run a real video through the converter. We measured every result: file size against MP4, and picture quality with VMAF.
Both numbers below come from converting the same video, not from a spec sheet. Size is relative to the MP4 output; quality is a VMAF score from 0 to 100. Green is best, amber is acceptable, red means a real penalty. See how we tested for the full method.
How We Tested Size and Quality
We did not copy numbers from a spec sheet. We took one real video, converted it to every format below with FFmpeg using the exact settings our in-browser converter uses, and then measured the actual output file size and picture quality.
ffmpeg -i source.mp4 -c:v libx264 -preset fast -c:a aac output.mp4Each format was encoded with its real encoder (VP9 for WEBM, H.265 for HEVC, MPEG-4 for AVI, and so on). Size is shown relative to the MP4 output. Quality is a VMAF score, Netflix's perceptual metric that compares every frame against the source: 100 is visually identical, above 95 is excellent, below 80 means visible loss. We cross-checked the low scores with PSNR and got the same result.
- Re-encoding an already-compressed file does not shrink it. Converting our MP4 to WEBM or HEVC produced a LARGER file, because you are re-compressing video that is already small. The "HEVC is 50% smaller" claim only holds when encoding from a clean master at matched quality, not when converting a finished MP4.
- Some conversions quietly destroy quality. AVI, DivX, Xvid, and WMV dropped to around 27 VMAF out of 100 at standard settings, and Motion JPEG was both the largest file and the worst quality (21 VMAF).
- MP4, WEBM, and AV1 keep quality highest (97 to 99 VMAF). Same-codec containers like MKV, MOV, and M4V match MP4 on both size and quality, so choosing between them is purely about where the file needs to play.
| Format | Codec | Typical Size | Quality (VMAF) | Best For | Support | Actions |
|---|---|---|---|---|---|---|
| MP4 | H.264 / H.265 / AV1 | Baseline | 97 VMAF | Everyday use, sharing | Universal | |
| WEBM | VP8 / VP9 / AV1 | ~1.2x MP4 | 99 VMAF | Web, HTML5 streaming | Modern browsers | |
| MKV | H.264 / H.265 / VP9 | Baseline | 97 VMAF | Archiving, multi-track | Players, not native mobile | |
| MOV | H.264 / ProRes | Baseline | 97 VMAF | Apple editing, Final Cut | Apple, editors | |
| AVI | MPEG-4 / DivX / Xvid | 79% of MP4 | 28 VMAF | Legacy Windows | Windows, old players | |
| HEVC | H.265 | 73% of MP4 | 94 VMAF | 4K, small high-quality files | Newer devices only | |
| AV1 | AV1 | ~1.1x MP4 | 98 VMAF | Next-gen web streaming | Newer browsers only | |
| FLV | H.263 / VP6 | 69% of MP4 | 83 VMAF | Legacy web archives | Obsolete (Flash gone) | |
| WMV | WMV / VC-1 | 97% of MP4 | 27 VMAF | Windows playback | Windows-centric | |
| M4V | H.264 | Baseline | 97 VMAF | iTunes, Apple TV, iOS | Apple ecosystem | |
| 3GP | H.263 / H.264 | ~1.1x MP4 | 97 VMAF | Old phones, MMS | Legacy mobile | |
| 3G2 | H.263 / H.264 | ~1.1x MP4 | 97 VMAF | Legacy CDMA phones | Legacy mobile | |
| OGV | Theora | ~2.0x MP4 | 99 VMAF | Open-source, Linux | Open-source software | |
| MPG | MPEG-1 / MPEG-2 | 85% of MP4 | 85 VMAF | DVD, VCD, broadcast | Broad (legacy) | |
| MPEG | MPEG-1 / 2 / 4 | 85% of MP4 | 85 VMAF | DVD, broadcast, streaming | Broad (legacy) | |
| DIVX | DivX (MPEG-4 ASP) | 79% of MP4 | 28 VMAF | DVD-era downloads | DivX-certified players | |
| XVID | Xvid (MPEG-4 ASP) | 57% of MP4 | 28 VMAF | Open MPEG-4 encoding | Media players | |
| F4V | H.264 | Baseline | 97 VMAF | Flash H.264 delivery | Obsolete (Flash gone) | |
| SWF | Vector / video | 69% of MP4 | 83 VMAF | Flash animations, games | Obsolete (Flash gone) | |
| RM | RealVideo | Not tested | Not tested | 1990s web streaming | Obsolete | |
| RMVB | RealVideo (VBR) | Not tested | Not tested | Early-2000s downloads | Obsolete | |
| VOB | MPEG-2 | 88% of MP4 | 85 VMAF | DVD-Video discs | DVD players | |
| TS | H.264 / MPEG-2 | ~1.1x MP4 | 97 VMAF | Broadcast, IPTV, capture | Broadcast, players | |
| MTS | AVCHD (H.264) | ~108% of MP4 | 97 VMAF | HD camcorder footage | Camcorders, editors | |
| M2TS | AVCHD / Blu-ray | ~1.1x MP4 | 97 VMAF | Blu-ray, camcorders | Blu-ray, players | |
| ASF | WMV / VC-1 | 97% of MP4 | 27 VMAF | Windows Media streaming | Windows-centric | |
| AVCHD | AVCHD (H.264) | ~108% of MP4 | 97 VMAF | Consumer HD camcorders | Camcorders, players | |
| M2V | MPEG-2 video | 66% of MP4 | 85 VMAF | DVD/broadcast video track | Editors, authoring | |
| MJPEG | Motion JPEG | ~6.6x MP4 | 21 VMAF | Capture, editing, webcams | Editors, cameras | |
| MXF | MPEG-2 / others | Not tested | Not tested | Professional broadcast | Pro broadcast gear | |
| WTV | H.264 / MPEG-2 | Not tested | Not tested | Windows Media Center DVR | Windows Media Center |
Sizes are relative to MP4 (H.264) at equal resolution and quality. Container formats assume their common codec. Actual results vary with your source, codec, and settings.
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