m4v M4V is a file format developed by Apple for the iTunes store's content and is very similar to the MP4 file extension. M4V is supported exclusively by Apple devices. Other video formats like MP4 and MOV can be converted to M4V in order to run on Apple devices. The most common difference between the M4V and MP4 formats is that M4V offers DRM-Copyright Protection which prevents the copyright of media content. To play a DRM-protected M4V file the computer needs authorization by opening the iTunes account used for buying the media file. However, if the files are not protected by DRM, the user can just rename the file extension from M4V to MP4 in order for it to be recognized by non-apple devices.
ogg The OGG file format and .ogg file extension refer to the open source container format developed and maintained by the Xiph.Org Foundation. The format has been in development since the early 90's and initially was designed as an open format for audio compression. Later iterations has seen the format revised into a full audio and video container format with compression codec support of different standards. OGG can be used both in compressed or uncompressed ways and is compatible with different lossy and lossless codecs both for audio and for video. Text can also be added into OGG files as an overlay, all packaged within a single file.