Note: The following was originally posted on twitter because I play around with video files a lot and I thought I’d answer some questions that people sometimes ask me.
Some of you might wonder about what I do when I say I losslessly remux FLV files from YouTube to mp4. Here’s an overview:
If you’re slightly familiar with YouTube formats, you’ll realise that YouTube uploads files in a combination of FLV and MP4. All HD formats (720p and above) are mp4s; all non-HD formats are in FLV/3GP (with the exception of 360p which comes in both mp4 and flv).
FLV and mp4s are essentially container formats (i.e. they contain video/audio streams that are encoded using certain codes).
For YouTube, all videos, no matter whether they are FLV or mp4, contain H264 MPEG-4 AVC video streams; audio are AAC streams.
So technically, all YouTube videos can be converted from FLV format to mp4 format without loss in quality.
