0FFmpeg LogoThe Ultimate Codec Guide

How data is stored in a multimedia file

Files on a com­puter (or on an optic­al disk like DVD or BluRay) need to con­tain more than 1 type of data.  A typ­ic­al movie will include at least 1 video “stream” and one audio “stream”.  Most movies include mul­tiple lan­guages and sub­titles, each of which requires an addi­tion­al stream.  Each of these streams is effect­ively a file in its own right, but they are all stored togeth­er with­in a “con­tain­er” which also starts each of them at the right time (sub­titles don’t start imme­di­ately at the start of a movie for example) and keeps them in sync as well as stor­ing meta-data about each of them – i.e. what lan­guage they are, what fram­er­ate and res­ol­u­tion the video is, and what com­pres­sion stand­ards have been used.

Video streams

Video streams con­tain only the video part of the movie.  They are com­pressed using a par­tic­u­lar sys­tem and there should be meta-data about their res­ol­u­tion, fram­er­ate, if they are inter­laced or pro­gress­ive and details of the encod­ing sys­tem used.

Audio streams

Audio streams con­tain only the audio part of the movie.  There are usu­ally mul­tiple audio streams included with the movie and each has its own stream.  They can be com­pressed in a range of ways or in some cases they are uncom­pressed raw audio.  There should be meta-data about their bitrate, res­ol­u­tion, lan­guage, num­ber of chan­nels and details of the encod­ing sys­tem used.

Oth­er streams (e.g. Closed Cap­tions)

Many movies con­tain oth­er streams, most com­monly closed cap­tions (also known as sub­titles).  These come in sev­er­al formats, but are typ­ic­ally just text with time stamps.  They are so small rel­at­ively that no com­pres­sion is used.  There should be meta-data about their lan­guage.


Con­tain­ers which bundle all the streams togeth­er

All of the streams that com­prise the movie are bundled togeth­er and kept in sync by a con­tain­er.  The con­tain­er should con­tain (and provide) all the meta-data about each stream.  The con­tain­er also enables the col­lec­tion of streams to be stored as a single file.  The most com­mon con­tain­er formats are VOB (used by DVD) and M2TS (used by BluRay).  Oth­er com­mon con­tain­er formats on PC are TS, MPEG, AVI, MKV, WMV, WTV, DVR-MS and MP4.  The obsol­ete HD-DVD format used EVO con­tain­ers.

Think we've missed something? Let us know by commenting below. If you would like to subscribe please use the subscribe link on the menu at the top right. You can also share this with your friends by using the social links below. Cheers.

You might also like...

Leave a Reply