Video Format Guide
After getting video resolution out of the way it's time for the other piece of the puzzle: video formats.
While a nice bright screen capable of high resolution video is all fun and games it's not really that useful if the player can only play video converted by hand by blind monks. Small players usually need converted files to play, bigger full blown PMPs don't. there's a jungle of formats out there and not always easy to keep track of what's what and what will work with which players. Read on for a guide on how to get through the jungle.
When playing with video formats, there are so much to keep track of that to be able to make sense of it all it needs to be simplified. A lot. I've been there, sitting hours on end staring at page long analyzes of h.264 files wondering what lumi masking and trellis quantization is and if that's whats making the player not accept the file. It's not fun, it's extremely confusing and it's not the way it's supposed to be. Therefor this article is for those of you who are beginners at video formats, not those of you with daily visits to the doom9 forum.
Container Formats
One of the biggest piece of misinformation out there with regards to video formats is the lack of knowledge about video container formats. .AVI isn't a video format. .MP4 isn't a video format (nor is it a name for video altogether as the Chinese manufacturers like to think). Video formats, also known as codecs, are basically methods of creating and playing back video. AVI, MP4, MKV are all container formats, which means they only contain the video files and the real video and audio files are inside. Think of it as a ZIP archive; a JPEG image file in a ZIP archive will be named .zip but it's still .jpg inside.
Video files work the same way; one shell (MKV, MP4, AVI etc) that contains one or more video files and audio files. MKV (aka matroska) is popular because it allows for several audio channels in one file and also subtitle files, making it perfect for high quality files with several audio tracks and subtitles - like anime. The AVI file you're used to seeing most likely contains a divX or Xvid video file and an mp3 file with the audio. Since the audio and video is separate, sync issues sometimes occur. While there are certain common usages for each file (which is why people think avi is avi) there are times where you might encounter problems that you can't understand why are there, and that'll most likely be due to the containers not containing what they normally do - put simply. These times you're better off just skipping that file if possible as such files often bring you hours of trouble with seemingly no logical solution.
Lastly, some companies like to "invent" new video "formats". By "one companies" i mean Samsung, their .svi file format is nothing but a restricted avi container and is most likely just there to make sure people use Samsung software to convert video. There are other to do so, so if you have a player that only accepts .svi - check the forums.
Bitrate
If everyone knew what bitrate was, we'd never have such questions as "how many CDs fit on 2GB". Bitrate is basically just how much space the audio or video file uses per second, measure in bits. One byte is 8 bits. The higher the bitrate, the bigger the file, and the better the quality will be because you'll have more space per second to avoid compressing the quality too much.
As an example, let's say you have a .AVI file thats 100 MB. Inside that AVI file is a MP3 audio file with a bitrate of 128 kbps ( kilo (thousand) bit per second) and an Xvid video file with a bitrate of 768 kbps. Combined that's 896 kbps, which is 112 KB (kilobyte, divide number of bits by 8 to get bytes). With 1024 KB per MB, we get 9,14 seconds of video and audio per MB. Since the file is 100 MB, thats 914 seconds - about 15 minutes 15 seconds. If the audio and video bitrate of the files inside the AVI is doubled to 256 and 1536 (respectively), the same 15 minutes 15 seconds of video will take up 200 MB. That's why the bitrate is so important in determining how much video you can get on a specified amount of space.
The recommended bitrate depends on resolution, video format, audio format and video type (animation, action etc). The higher the resolution, the more space is needed for a good quality image. With audio and video formats, some are better to compress the audio/video stream so you get better or worse quality with the same bitrate compared to another format. The video type also matters, because you need more space for all the color information in an action scene with lot of things going on than you need in an animated scene with the same basic colors everywhere. Save a monocolored picture and a complex picture as a jpeg and see for yourself.
Frame Rate
Frame rate is how many pictures per second that the video consists of, normally 25 or ~30 (some go as low as 15, that makes for choppy video). 25 FPS is PAL video (Europe), 29.971 FPS is NTSC (US). this has nothing to do with where your player is from and is related to TV broadcasts. The higher the better, but both 25 and 30 should be sufficient, and increasing frame rate to a higher one than the source file has no purpose whatsoever.
Frame rate isn't really anything you should concentrate too much on, the only reason I mention it is that some players can only play 15 FPS which is bad and some manufacturers use the max FPS as an advertising thing (which is rather pointless).
Audio Formats
The audio format used doesn't do to much for people that use normal video converters to convert video, but it's still worth mentioning. Inside the container files you have at least one audio and one video file (if it's a normal video with sound). Some players only play a specific audio format for video and might also be picky about the bitrate of the audio file, for example the Cowon D2 only plays video with MP3 audio.
Other audio formats that players might require are WMA for WMV video and AAC for h.264. Unconverted video straight off the web might have AC3 audio (Dolby Digital). The best thing is to just let the converter handle audio, as long as you have a converter profile or application specifically for your player.
Video Formats
MPEG-4
MPEG-4 and MP4 confuse people for a reason. While MP4 is a container, it contains MPEG-4 video. MPEG-4 is simply put the basis for a lot of video formats you might have heard of, like DivX, Xvid, h.264 and even Quicktime. The problem is that many media player manufacturers don't specify what the player can actually play, but might just say it supports AVI or MPEG-4. While technically true, it's like saying a car runs on fuel; it's true, but it doesn't help you when you're at the gas station and you have both gasoline and diesel pumps. Both are fuels, one will work, one will not.
MPEG-4 might be a 1080p high definition h.264 encoded file or it might be a low resolution small Xvid file. To make it even more confusing, there is a "generic" MPEG-4 format which for example the iPod can play that is what Xvid and DivX builds upon. Bottom line you should check what kind of video formats the player really plays - there is no such thing as "plays MPEG-4".
DivX and Xvid
With regards to DivX vs Xvid, Xvid is basically open source DivX. Xvid is what's in those torrented Prison Break AVI files that you don't have on your HDD because it would be illegal and it's what most people think of when they refer to AVI files (not knowing AVI is a container format, of course). There is a reason why Xvid is popular; it works. It's not the best video format out there (compared to say h.264), but it gives you the best quality/effort ratio. It's common, easy to convert and generally a very usable format.
Players that support this format (with conversion) include for example the Cowon D2 and the Creative Zen. Please be very aware that when companies advertise DivX support on small players, you do have to convert those torrented files you don't have - they won't play directly. Such small players only accept DivX/Xvid with a specific resolution, bitrate, and audio format. The best way to make sure you get the correct format is to use the supplied conversion software (that goes for all players) but you'll get better quality from looking through forums and guides on how to convert video specifically for your player.
h.264
h.264 is also a MPEG-4 format but based off another part of MPEG-4 than DivX and Xvid. h.264 is the most popular format out there when it comes to "bang for the buck", meaning you'll get better quality at the same bitrate with h.264 than you will with Xvid.
The downside is that it demands much more from your computer (and playback device for that matter) to convert and play it than it does from other formats. It takes longer, but you get off with better quality per bitrate. It's also a very complex format with a lot of things that can go wrong if you don't use idiot proof software and the players that can play this format are very limited to what they will accept. h.264 is popular for HD content (which no portable player can really play, but some think they can) and also for video podcasts. h.264 is used by players such as the iPod, Sansa View, Zune, Sony NWZ video players, PSP and it's also supported (with less restrictions) by bigger full blown PMPs such as the Cowon A3. The good thing about having a player that can play h.264 is that if it supports the same profiles as the iPod it can use already available iPod content such as video podcasts.
Windows Media Video (WMV)
Windows Media Video normally use the ASF container and the files end in either .wmv or .asf. The file ending is irrelevant and you could rename asf to wmv and it would still work. WMV is a group of codecs just like MPEG-4 but the most common video format used in portable players is some crippled version of WMV 9. Microsoft of course claims that WMV is better than everything else, but for portable players history has shown a lot of audio sync issues with the format. WMV is also used by the PlaysForSure service which is a standard set by Microsoft for devices that fulfill certain criteria and can play back the "standard" DRMed WMV format - such as Amazon video and DVD Digital Copy uses. Players that support WMV include the Creative Zen, Cowon D2, Creative X-Fi, iriver SPINN and others.
Motion JPEG
M-JPEG aka Motion JPEG is basically the worst format your player can play. It's basically just JPEG images making up a video file which means you need a very high bitrate to get even remote useful quality on even low resolution screens - the nly good thing is that it needs very little CPU power to encode. This format is often used on players that have video support only as a gimmick and should not be used for video. Players using this include the Sansa E200 and Creative Mozaic.
MPEG-2
MPEG-2 is the standard for DVDs, certain streaming videos and also some content you find on the internet. More or less only big full blown PMPs support this format and it's mostly used for DVD ISOs, so it's not really important unless you have a giant harddrive and plan to use that feature.
RealVideo
RealVideo is a format that extremely few players use; in fact I haven't seen any player outside Asia supporting this. The only reason I mention it is that you might come across it from time to time, in which case my advice is to throw it out. It's not very compatible with players or video converters and will likely cause you trouble if you're planning on getting it on a PMP.
What Should I choose?
Now that both video resolution and video formats have been covered, it's down to picking a player. When doing so you should ask yourself if you watch a lot of video, where you get the content and where you are when you watch. If you need a player for watching downloaded TV shows daily on a long bus ride, a full blown PMP like the Cowon A3 or Archos 5 would be best because you have support for most formats without conversion and you have a big high resolution screen.
For more casual use, a smaller player is good for portability and music playback battery life and here you should look at what content you use. If you want to use your own content, something that plays converted Xvid (like the Cowon D2) is best because it's faster to convert. If you like video podcasts (like I do, Tekzilla FTW) a video podcast compatible player like the Sony players or the Zune would be a better choice - however with these players converting your own content will take longer.
What you should never do is buy players like the Creative Mozaic or Sansa E200 for video purposes, these players don't have the screen size nor the video format compatibility required for decent video viewing. Whatever you end up with, if you plan on watching video check these things before buying so you don't end up with something you can't use. Also remember that this is all tech specs and you should read reviews for real life experiences to make sure there aren't any critical problems beyond what the tech specs show you.
Those of you who want to know more about video formats and how to get the best quality for your player, you should check out VideoHelp and Doom9. Just be aware that it's not as easy as it might sound.
Comments
Jessica on November 3, 2008 11:41 AM
great write up! and I love the comparisons to everyday situations (like the car fuel, etc), helped me understand way more
it's still quite confusing but I would most likely go with the software converter that came with the pmp
just wondering though, for videos off of youtube that are highly pixelated and bad quality, is there any way to convert it so that on the pmp it LOOKS better?
sprockkets on November 3, 2008 3:30 PM
Please, please educate people on profiles that exists in MPEG4 SP/ASP and MPEG-4 Part 10/H264! Too many people don't understand why a certain Xvid encode will not work on a portable device even if it has the right resolution and container format and audio format!
merc510 on November 3, 2008 3:31 PM
How about players like the zune which support 720x480 tv-out resolution, does the video have to be encoded in that resolution or does the player upscale the 320x240 when connected to the tv?
Zaied on November 3, 2008 3:32 PM
Great article! I was always confused about a player that accepted divx/xvid but required "conversion". It was never clear what that really meant (conversion to another format or resolution/bitrate?)
Jay on November 3, 2008 3:51 PM
Quick question, If I have the same audio and video file and encode in both h264 and xvid, does h264 end up being the smaller file than xvid when all else is the same?
sprockkets on November 3, 2008 5:34 PM
@Jay Yes and no. x264 will look better if the same features and bitrate are selected. But x264 can compress even more with additional features not available in MPEG-4 ASP and still look better, at the cost of encoding and decoding processing power.
The file size can end up being the same depending on what settings you use for bitrate constraints (such as two pass encoding at a set video size), but the x264 encode will always look better.
Going back to profiles however, some players like the lousy ipod/itouch, handle only h264 at the SP or simple profile level, which means no advanced features or even b-frames. If you encode h264 at the SP level, and xvid at the ASP level (qpel, gmc, b-frames), the xvid encode might look just as good or even come out smaller.
FYI, the Cowon D2 does MPEG-4 SP, or no qpel, no b-frames and no gmc. The A3 as of recent firmwares supports the HP, or high profile of h264, which is very nice considering most HD encodes use all the advanced features of the format to save space, albeit at the expense of processing power.
Andreas Ødegård on November 3, 2008 5:41 PM
@Jessica: Unfortunately, converting to better formats don't solve bad quality issues. To do a car simile, it would be like painting an old car without fixing the engine and expect it to go faster because it looks prettier.
@merc510: It does upscale, but you will always get better quality if you convert to the max resolution/TV resolution (if max resolution is higher than tv resolution).
@sprockkets: I agree, but that tends to be a bit technical. With h264 even using the wrong level with everythign else right can make the file incompatible with certain players (PSP PSP PSP PSP PSP did i mention the PSP?) and dont even get me started on broken headers >.
sprockkets on November 3, 2008 6:12 PM
Hmmm... if the tool in avidemux is correct, then the PSP can handle h264 video at 720x480, at 768kbps, with aac audio, and no deblocking filter, no partition macroblocks, and no chroma ME, no mixed refs. This is better than what the SP profile of h264 defines, or what the ipod/itouch can handle.
While it may be technical, this helps people to understand what is going on. Instead of saying how no player supports "generic MPEG-4," manufacturers should say that if a player can play MPEG-4 ASP, then that means a Divx/Xvid encode with features such as b-frames, qpel, and GMC if selected. Otherwise, it pisses me off to buy a Divx certified DVD player, only to find out it can't even handle a feature as simple as b-frames, which for both Xvid and h264, is the prime way of compressing the video stream.
Andreas Ødegård on November 3, 2008 6:53 PM
@sprockkets: As interesting as video codecs might be to some people (me included), its still not somethign the normal consumer that buys a mp3 player needs to know. It will only confuse people, heck, even this guide might confuse people. Noone was built with doom9 loaded into their head, it's a hobby like everything else. To again use a car simily, people don't need to know how to fix a car to drive one - but it's useful to be able to change oil, tires and fill it up with gas. This guide is the video codec version of that - anyone that wants to learn how to be a mechanic can study on their own turn, but i doubt 1% of people reading this will actually do so. Forum users and commenters make up a very small percentage of people actually reading these guides.
Ferd Burfel on November 3, 2008 7:28 PM
"Lastly, some companies like to "invent" new video "formats".
Been there, done that.
Panasonic has a line of security monitors that saves in "h3r" format. The only way to view them is with a proprietary viewer file, which one must be sure to include with the files when providing them to law enforcement. I've found nothing else that reads them or coverts them. What a PITA.
kugel on November 4, 2008 11:09 AM
Great article.
I didn't like the mpeg2 part though. It's the format supported by Rockbox (and thus plays on every Rockbox'd targets). The format is quite effective and you can get reasonable quality on low bitrates, such as 500kbit/s. Surely there's better formats, but it can definitely compete with xvid.
And it doesn't use much cpu power. It plays very well on a e200, of which the OF only gave MJPEG. Mpeg2 plays better than mjpeg on it.
AC on November 4, 2008 4:50 PM
You know, I'm really appreciating this site a lot more. You guys provide very useful and well presented information here. Exceptional.
YerMum on November 4, 2008 5:56 PM
"...blind munks" ? you mean Alvin, Theodore and Simon?.....hmmm you probably meant "monks" like in the celibate religious type lol
Andreas Ødegård on November 4, 2008 6:04 PM
@YerMum: Indeed. Martin (dfkt) actually read it before publishing and said the exact same thing (with the chipmunks) but i forgot to chang eit. Fixed now, thx
whackpak on November 4, 2008 7:02 PM
good text!
I like to see more of this!
Martin Sägmüller on November 5, 2008 11:25 AM
@kugel: In no way can MPEG2 compete with MPEG4-SP formats like XviD, compression/quality-ratio wise. "500kbps" doesn't mean anything if you don't mention the display size. 500kbps is maybe enough for MPEG2 at 220x176 on your Sansa, whereas XviD would look the same (or even better) at 250kbps for 220x176.
Hillshum on November 12, 2008 8:30 PM
I might add that the Sansa e200v2 (which is what SanDisk has mainly been selling for almost a year) Will play DivX
greg on November 25, 2008 8:53 PM
Is there a chart somewhere, where it shows you exactly what players can play what specific formats.
I'm not talking about simply, mp4, xvid, h264, aac...
I'm talking about a chart with all that technical mumbo jumbo.
Like:
Xvid, Level 3, Simple Profile;
AVC, Baseline Profile, Level 2.0;
Mpeg4, Main Profile, Level 5.1;
AAC Low Complexity, SSR, HE-V2;
etc, etc.
q on February 9, 2009 5:13 PM
"Video formats, also known as codecs, are basically methods of creating and playing back video. "
Formats are not codecs.
naresh singh rathore on April 20, 2009 12:39 PM
sir i have a video clip in .vid extension file taken by my china made mobile . i can't play this file in my PC .
Koo on September 1, 2009 4:39 AM
Hoe can I trascode blueray discs
to watch on my Creative Zen Vision