What Is H.264, and Why Does MP4 Play Almost Everywhere?
If you have ever wondered why "convert it to MP4" is the standard advice when a video will not play, the answer is mostly H.264. This article explains what that is, in terms that do not require any technical background.
What a video codec does
Raw video is enormous. A minute of uncompressed full-HD footage would take many gigabytes. A codec (short for coder-decoder) compresses video so it fits in a manageable file, and the same codec decompresses it again for playback. Compression works by storing the differences between frames rather than every frame in full, and by discarding detail that people are unlikely to notice.
H.264 in short
H.264, also called AVC (Advanced Video Coding) or MPEG-4 Part 10, was standardized in the early 2000s. It reached a good balance between compression efficiency and the amount of computing power needed to play it. Over time almost every phone, computer, set-top box, television and game console gained hardware that can decode H.264 efficiently. Because so many devices can play it smoothly and without draining the battery, H.264 became the default choice for video on the internet.
Newer codecs such as HEVC (H.265), VP9 and AV1 can produce smaller files at similar quality. The catch is compatibility: older devices, some browsers and some software cannot play them, or do so slowly. A file that is a few percent larger but works for everyone is often the better choice.
The role of AAC and MP4
- AAC is the audio codec most often paired with H.264. It gives good quality at modest bitrates and is widely supported.
- MP4 is the container that holds the H.264 video and the AAC audio together, along with information like duration and timing.
The combination of MP4, H.264 and AAC is therefore the safest "everyday" choice for sharing video. When you pick MP4 on Free Video Converter, that is exactly what you get.
Technical details behind the MP4 setting here
For readers who want to know what the converter does, here are the real parameters of the MP4 preset:
- Video codec: H.264, encoded with the x264 encoder.
- Quality: a constant rate factor of 26 with the fastest preset (ultrafast), which trades some file size for speed. A lower number would mean higher quality and bigger files; 26 is a moderate setting aimed at keeping conversion times acceptable.
- Pixel format:
yuv420p, the format that most players and hardware decoders handle. Using it avoids files that open on a computer but fail on a phone or TV. - Audio: AAC at 128 kbps.
- The file is laid out so playback can begin before it has fully downloaded, which is useful for web use.
Is H.264 always the right choice?
No. If you are delivering video to a website that serves modern browsers and want the smallest files, newer codecs may be worth the extra effort. If you need to keep several audio tracks, subtitles or chapters, the Matroska (MKV) container is more flexible; see converting MKV to MP4 for that trade-off. For the typical case of "I need this video to work on someone else's phone", H.264 in MP4 is hard to beat.
A note on patents
H.264 is covered by patents managed through licensing pools, which is one reason open alternatives such as WebM (VP8, VP9, AV1) exist. For ordinary users converting their own files this is not something you need to deal with directly, but it explains why you will see both families of formats online. For more on the open alternatives, read when to use WebM.
Ready to try it? Convert your video in the browser, no upload and no sign-up.
Open the converter