How big MPEG video really is
MPEG-2, the codec inside most .mpg files, dates from the 1990s. It needs roughly twice the bitrate of H.264 for the same picture. DVD recorders and TV capture devices typically record at 4 to 8 Mbit/s, which is about 1.8 to 3.6 GB per hour at standard definition. A few recorded films or a box of transferred home videos can fill a drive quickly.
MPEG-1 files are smaller because the picture is smaller, usually 352×288 or 352×240. They mostly come from Video CDs and very early digital cameras.
Why stay with MPEG
The main reason to compress into MPEG instead of converting is the playback device. Many DVD players with a USB port, older smart TVs, set-top boxes, DVD authoring programs and broadcast tools accept MPEG-2 and nothing newer. Compressing keeps the file compatible with them while using less space.
The compressed file has MPEG-2 or MPEG-1 video and MP2 sound, the classic combination these devices expect. It is written by a built-in converter engine (ffmpeg compiled for the browser), because browsers can't decode or encode MPEG video themselves. This is slower than compressing MP4, and the whole file has to fit in the browser's memory.
Where the savings come from
MPEG-2 doesn't cope well with low bitrates. Below a certain point, the picture breaks into visible blocks, especially in dark scenes and fast motion. A large saving at full DVD resolution is therefore limited. These steps work better:
- Lower the resolution. 480p or 360p needs far fewer bits per frame, and on a small TV the difference is modest.
- Use the preview on a dark scene. The 2-second comparison with 2× zoom shows blocking early.
- Keep the frame rate. PAL video runs at 25 fps and NTSC at about 30 fps. Changing it can make motion jerky on TVs.
- Choose MPEG-1 only when you must. It is less efficient than MPEG-2 and meant for very old players.
If the format doesn't matter
When the video will be watched on a computer, phone or modern TV, an MP4 with H.264 gives a far smaller file at the same quality. Use MPEG to MP4 for that. Recordings split into several parts can be joined in the MPEG editor, which also removes adverts and blank minutes at the start of a TV recording. For mixed batches of formats, there is Compress Video. Your recordings stay on your device the whole time.