Glossary
What is an MP4 file?
By the KeyMo team · Updated
MP4 is a common video file format, defined as the MP4 file format in Part 14 of ISO/IEC 14496. It is a container: one file that wraps video and audio tracks, and what is inside can differ. YouTube recommends MP4 with H.264 video and AAC audio, and KeyMo accepts MP4 uploads.
MP4 meaning in simple words
Think of MP4 as the box and the video as what is in it. The box (container) keeps video, audio and the information that ties them together. The video inside is squeezed by a codec such as H.264 and the sound by one such as AAC. Two MP4 files can look the same from the outside and behave very differently because of what was packed in.
The ISO catalogue lists the standard as ISO/IEC 14496-14:2020, part of the "Coding of audio-visual objects" series, and says it defines the MP4 file format as derived from the ISO Base Media File format.
| Layer | Example | Job |
|---|---|---|
| Container | MP4 | Holds the tracks together in one file |
| Video codec | H.264 | Compresses the picture |
| Audio codec | AAC | Compresses the sound |
MP4 is a video format, so it is not the same as an MP3, which stores sound only. See codec for the rest of the vocabulary.
What YouTube asks for in an MP4
YouTube's own page is one of the few places that spell out settings, and they are recommendations, not limits.
| Setting | YouTube recommendation |
|---|---|
| Container | MP4, no edit lists, moov atom at the front of the file (Fast Start) |
| Video codec | H.264, progressive scan, High Profile |
| Audio codec | AAC-LC, Opus or Eclipsa Audio |
| Audio sample rate | 48 kHz |
| 1080p SDR video bitrate | 8 Mbps at 24, 25 or 30 fps; 12 Mbps at 48, 50 or 60 fps |
| Stereo audio bitrate | 384 kbps |
| Interlaced footage | Deinterlace before uploading |
File-size maths for long recordings
A podcast is long, so file size is the practical limit. Take YouTube's 8 Mbps for 1080p video at 30 fps and 384 kbps for stereo audio, which is 8.384 Mbps together. One hour comes to about 3.8 GB (decimal), 90 minutes to about 5.7 GB, 2 hours to about 7.5 GB and 3 hours to about 11.3 GB. That is arithmetic, not a KeyMo measurement, and your own export may use a lower bitrate.
KeyMo accepts MP4 or MOV uploads from 5 minutes to 3 hours, up to 10 GB. A 3-hour export at the bitrate above would be over that limit, so lower the bitrate or split the recording. The video file size calculator does the sums for your own settings.
Common mistakes
- Treating the extension as a guarantee. A .mp4 file can hold a codec some devices cannot play.
- Forgetting that moov atom placement matters. YouTube asks for it at the front of the file.
- Uploading interlaced footage without deinterlacing it first.
- Chasing a huge bitrate for a talking-head podcast and then running into file limits.
Where KeyMo touches it
Upload an MP4 or MOV and KeyMo returns up to 15 vertical clips at 1080 by 1920, 30 fps, with H.264 video and AAC audio.
Sources: ISO/IEC 14496-14:2020 MP4 file format (ISO) (checked 11 October 2026); YouTube recommended upload encoding settings (YouTube Help) (checked 11 October 2026); Supported YouTube file formats (YouTube Help) (checked 11 October 2026).