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I tried googling this but I didn't actually find any conclusive evidence to sustain this so I'm going to present my case.

A couple of years ago I took the time to convert all our family video tapes into digital copies on my computer. This was done by "recording" the original tapes by playback onto a RW CD/DVD, and then copying the CD contents onto the computer. The result was that all these files were stored in MPG format. I gathered approximately 120gb worth of storage for something around 18.5 hours of video footage.

I recently decided to take a look at these files in order to make some sort of video collage for my mother's birthday and while cutting and copying the files I noticed for example that a simple 2 min video was over 100mb in size (just to illustrate the difference this a video of 2 min sent on Whatsapp is about 3-8mb - not a great example since Whatsapp severely reduces video quality but it's still considerable). Now I'm sure that when dealing with high quality and high resolution footage that this is probably a tiny amount, but I'm not exactly dealing with high quality video right here. I think I posted one of these videos on Youtube once and it capped out at 480p. So I opened Handbrake and used it to convert a 7 min 450mb MPG file to MP4 and it got cut down to 85mb with no considerable quality drop (if any for that matter).

So this brings me back to my question; is MPG some sort of lossless format that stores much bigger files? Or is it maybe just "outdated" (I wouldn't know if this even applies to video formats)? What I'd really like to know is if it's a bad idea to reformat all the video files to MP4 or MKV and work with those instead of sticking with the much bulkier MPG files (that don't seem to have any considerable advantage over the other ones at the moment).

For clarity's sake I'm including pictures of a before and after Handbrake encoding of a 2 min video:

Before encoding - MPG format: Before encoding - MPG format

After encoding - MPG format: After encoding - MKV format

Andres Stadelmann
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2 Answers2

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  • First thing first: What does digital video consist of?

    Digital video files are very complex files. These files are usually in one of the known container formats. The container format defines how audio tracks, video tracks, subtitle tracks and chapter tracks are laid out in a file that ultimately becomes a digital video file. The first two elements themselves can be very complex too and are usually encoded in one of the well-known video formats and audio formats.

    Most of the times, however, you cannot guess what is the container format, audio format or video format by just looking at the filename extension. Take .mkv for example: It is the extreme case scenario, as it can contain literally anything, not just audio, video, subtitle and chapter!

  • So, what is an .mpg file? A container format? Audio format? or video format?

    Valid .mpg files are container files for digital video whose format is either the one defined by the part 1 of the MPEG-1 standard, or the one defined by part 1 of the MPEG-2 standard. Their video and audio tracks, however, can only be certain things:

    • The video format can only be the format defined by either the part 2 of MPEG-1 or the part 2 of MPEG-2 standards. (People often skip the part number and just say "MPEG-1 video" or "MPEG-2 video".) The MPEG-2 Part 2 video is also known as H.262. MPEG-1 video is also used in the old Video CD format. MPEG-2 video is part of the notorious DVD-Video standard.
    • The audio format can only be one of those three formats that are defined in the part 3 of MPEG-1. (Yes, part 3 defines three different formats.) I bet you have heard the name of one of those three: MPEG-1 Audio Layer III, widely known as MP3! The part 3 of MPEG-2 standard just augments the part 3 of its MPEG-1.

  • Is the MPEG-1 standard outdated?

    Yes; considering both its date and its successors, it is outdated. MPEG-1 is devised in 1988. Its video format is first published in 1993. On the other hand, the video format is deprecated by its successors (sorted chronologically):

    The audio format is also deprecated in favor of newer ones: MPEG-2 Part 7: AAC and MPEG-4 Part 3: AAC. Even the container format itself is deprecated by MPEG-4 Part 12 and MPEG-4 Part 14 (better known as "MP4").

  • Is it lossy?

    Yes. The MPEG family of formats are all lossy.

  • Is its size because of its age?

    Yes and no. In a lossy video format, the size of a video is determined by the target bit rate, expressed in bits per second (bps). The higher the bit rate, the bigger the video. You can lower the bit rate all you want; the size drops with it, but so does the quality (to the point of the video being just a wall that changes color once in a while!)

    Video format (and also audio format; let's not forget that) has a decisive impact: The better the video format, the higher the quality for a given bit rate. For example, at 700 kbps, your Half-HD video (720p) would look very satisfactory if it is in H.264 format, but not so if it is in MPEG-1 video format.

    Encoder quality is also very decisive. It is not just important to choose the right video format; it is also important to choose the best software that produces that video format. For example, libx264 generates much better H.264 video than QuickTime.

    There are many, many, many other fine deciding factors too. For example, does the app that creates a silent video generates just a video track? Or does it generate a video track along with an audio track containing silence? (The latter is wasteful.) The container format has an effect too. You will find that an MPEG-4 Part 4 (ASP) video track inside a .avi or .divx container file occupies a lot more disk space than when the same track is in a .mp4 or .mkv file.

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MPG is normally associated with MPEG2. This is an old compression format which requires very little (by modern standards) processing power to encode/decide - but creates large files. MPEG2 is outdated for the most part, but does still have uses - particularly in broadcast.

MPEG4 typically hold files compressed with newer cidecs which are much more bandwidth efficient - at the cost of a lot more processing overhead.

MPEG2 and MPEG4 both employ lossy codecs - the amount of loss will depend on the settings used to do the compression - you will loose at least a bit of quality when transcoding from MPEG2 to mpeg4 - whether it's worth the saving is dependent on you.

As indicated, mpg and mp4 are container formats for other codecs, so it is possible to have different quality / performance types within each format - but with MPEG2 it's typically an mp2 stream with differences in audio, while mp4 typically uses h.264, divx or better - all much tighter, more processor intensive formats.

davidgo
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