What .mpg and .mpeg actually are
Both extensions point at the same thing: an MPEG-1 or MPEG-2 program stream. This is the format of Video CDs, DVD video titles, late-90s and early-2000s digital cameras, and the analog TV-capture cards people used to digitize VHS tapes. The extension is purely cosmetic — .mpg and .mpeg are interchangeable, which is why this tool accepts both.
What this tool does, exactly
Native server-side ffmpeg decodes the MPEG-1 / MPEG-2 video stream, re-encodes it to H.264 at CRF 23, re-encodes the audio to AAC at 160 kbps, and writes the result as an MP4 with the +faststart flag so it begins playing immediately when streamed. Pixel format is forced to yuv420p so the output decodes on every modern player and hardware chip. It is a single file in, a single MP4 out — no options to tune.
Why MPEG files are large yet won't play
An old MPEG-2 DVD rip can be hundreds of megabytes for a few minutes of standard-definition footage, yet phones, browsers, and editors still refuse it. MPEG-1 and MPEG-2 compress far less efficiently than H.264 — they spend a lot of bits on mediocre picture — and the codecs are old enough that modern decoders have quietly dropped reliable support. Re-encoding to H.264 + AAC inside an MP4 wrapper produces a smaller file that actually opens everywhere.
Sister tools
For other broadcast and capture containers, TS to MP4 converter handles MPEG transport streams from PVRs and IPTV, and MTS to MP4 converter handles AVCHD camcorder footage. For other legacy files, AVI to MP4 converter covers DivX and Xvid, while MOV to MP4 converter handles QuickTime sources. Shrinking a finished MP4 further? Video compressor.
Skipping the conversion entirely
MPG and MPEG exist because old discs, cameras, and capture cards created them. If you are still producing new content and ending up in MPEG, consider switching to a recorder that outputs MP4 directly. Clipy records your screen straight to a shareable link — no local file, no format conversion, no watermark, no install.