MP4 FAQ

[bond]

1) What is MP4? I have heard it is a "container format"? What's that?
A container format allows you to combine different multimedia streams (most of the time audio and video) into one single file.
Multimedia containers are for example the well known AVI (.avi), MPEG (.mpg, .mpeg), Matroska (.mkv, .mka), OGM (.ogm), Quicktime (.mov) or Realmedia (.rm, .rmvb)

MP4 is the global file extension for the official container format defined in the MPEG-4 standard (ISO 14496-14)
MP4 is streamable and supports all kinds of multimedia content (multiple audio-, video-, subtitlestreams, pictures, variable-framerates, -bitrates, -samplerates...) and advanced content (officially called "Rich Media" or "BIFS") like 2D and 3D animated graphics, user interactivity, DVD-like menus... - next to nothing handled by the often used AVI

2) What extension is MP4 using?
- .mp4: only official extension, for all audio and video and advanced content files (and combinations)

other related extensions:
- .m4v: .mp4 files with the WRONG extension introduced by apple for video+audio files, m4v can safely be renamed to .mp4
- .m4a: .mp4 files with the WRONG extension introduced by apple for audio-only files, m4a can safely be renamed to .mp4
- .m4p: DRM protected files sold in iTunes, using the DRM sheme developed by apple
- .m4e: renamed .sdp files used by Envivio for streaming
- .m4v, .mp4v, .cmp, .divx, .xvid, .264: normally raw mpeg-4 video streams (not inside MP4)
- .3gp, .3g2: used by mobile phones, can also include content not defined for .mp4 (H.263, AMR)

3) How can i create spec compliant MP4 files?
easy answer: have a look at Doom9's MP4 Guide or Nero Recode2 Guide

detailed answer:
1) To create MP4 files you should preferably use audio/video formats covered by the MPEG-4 Standard:
- MP4 video formats: MPEG-4 SP/ASP: XviD, DivX5, 3ivx, ffmpeg/ffdshow, NeroDigital ASP... and MPEG-4 AVC/H.264: x264, NeroDigital AVC, Apple... and MPEG-2, MPEG-1 (not DivX3/MS Mpeg-4, WM9, RV9 or VP6) - doom9's quality comparisons: 1 2
- MP4 audio formats: Advanced Audio Coding (AAC FAQ): Quicktime/iTunes, Nero, Psytel, FAAC (binary)... (rjamorim's quality comparisons: 1 2) and MP3, MP2, MP1, CELP (speech), TwinVQ (very low bitrates), SAOL (midi), ALS (lossless)
- MP4 subtitle/text format: MPEG-4 Timed Text (see question 7)
- MP4 picture formats: JPEG, PNG

2) with the following tools you can mux MPEG-4 compatible content into the MP4 container:
- GPAC's MP4Box, commandline, supports AVC, packed b-frames, advanced content/BIFS, TTXT and Chapters (Doom9 Guide)
- MPEG4IP's mp4creator, commandline, able to mux AVC, dont use it with AVI and packed b-frames!
- 3ivx mp4 muxer dshow filter, usable in Graphedit, supports packed AVI b-frames but no AVC (3ivx Guide)
- mp4UI, based on MPEG4IP, dont use it with AVC, AVI and (packed) b-frames!
- VideoLAN, able to mux AVC, dont use it with (packed) b-frames!
- ffmpeg, buggy, commandline, especially dont use it with AVC, AVI and (packed) b-frames!
- IBM's Toolkit for MPEG-4 which includes XMTBatch and/or AVGen (also a simple version) based on Java
- dvd2mp4gui, GUI using mp4tool, supports muxing multiple audio and subtitle streams (as advanced content) into MP4
- mp4tool/mp4edit from ENST, supports BIFS, mp4edit is the "light" GUI version of the commandline mp4tool
3) the following "all-in-one" MP4 encoding tools are existing:
- Nero Recode2, encodes into MP4 using ASP or AVC and AAC (Doom9 Guide), subs are DVD VobSubs, includes a dshow muxer
- Doom9's MeGUI, supports ASP (Xvid, libavcodec), AVC (x264) and AAC (Besweet - Nero) encoding
- HDX4 supports ASP and AAC
- Dicas' mpegable X4 live, encodes into MP4 using Dicas' codecs
- Envivio's 4Coder encodes to MPEG-4 AAC, ASP/SP and AVC
4) the following tools can be used for editing (eg splitting, appending) MP4 files:
- MP4Box splits MP4 (AAC, ASP, AVC, TTXT, MPEG-1/2, private streams) time- and sizewise, extracts parts and joins MP4 too
- Ulead's VideoStudio 8 with the MPEG-4 plugin
- Sony's Vegas 6
- Quicktime/Pro can be used to create (encode, mux) and edit (split, join) MP4 files, supports MPEG-4 Simple Profile, AAC, AVC

4) Is it also possible to place streams not covered by the MPEG-4 standard in MP4?
Yes, altough i dont like the idea of doing so, the MPEG-4 standard defines how to place any stream in MP4. Similar to how streams are marked in AVI with private FourCCs, in MP4 they get a "private track ID". Note that no player will be able to handle such streams in MP4, but will simply ignore them, if not explicitely specified to do so
the following streams, not covered by MPEG-4, can be placed in MP4 already:
- Ogg Vorbis and Ogg Theora, via MP4Box
- Ogg Vorbis, via a patched mp4creator
- Apple's Lossless Audio (ALAC/ALE - not compliant with MPEG-4 ALS), via iTunes
- DVD picture subtitles (Vobsubs), via Nero Recode2
- AMR Speech Audio, via the NEC e808/e616 mobile phone
only the future will show if these private streams will be widely accepted and supported...

5) What do i have to especially look at, when i mux MPEG-4 video from AVI to MP4?
there are potential problems when muxing from AVIs (especially with b-frames/B-VOPs/bi-directional encoding) into MP4:
1) "delay frames", caused by the old VFW interface some codecs still use (XviD, DivX5). only when encoding with VirtualDub/Mod these will be automatically dropped when using b-frames
2) "packed bitstream", caused by the old AVI container, which is not really capable of storing b-frames. PB is used in DivX5 (only with 1 consecutive b-frame set) and by default in new XviD builds (make sure the PB option is unticked in XviD) and packs b-frames together with other frames (read a more detailed description about B-frames in AVI here).
3) "userdata", which in the case of XviD and DivX PB streams signals the useage of PB. some decoders take this flag into account while decoding
4) "vol", which is placed on every keyframe in AVI, but has to be seperated from the movie data in MP4
5) "ctts" atom, which has to be written when muxing b-frames into MP4

Currently only the 3ivx mp4 muxer and GPAC's MP4Box handle all these things correctly! use only them for AVI conversions, especially with packed bitstreams or if you are unsure which b-frame option/encoding app was used. otherwise the chance is great that you will not get a 100% spec compliant MP4 file!

6) Does transmuxing to MP4 reencode the content?
No, this is a lossless process, only taking out the media streams from one container and putting them into MP4

7) How can i mux Subtitles into MP4 files?
there are three possibilites to store subs in mp4:
- In contrary to MPEG-1/2 the MPEG-4 Standard defines its own Text Stream/Subtitle Format under ISO 14496-17 (MPEG-4 Timed Text). Its text-based (not picture-based as DVD subs), uses UTF-8/16 (including cyrilic, arabic, chinese characters...), allows all sorts of animations (scrolling, colors, karaoke aso...), allows attaching of fonts and is streamable
MPEG-4 TTXT creation is already supported in MP4Box and Quicktime. Playback works with Gabest's and Haali's MP4 dshow parser, Osmo4, Realplayer and Quicktime (only when placed in .3gp) and VideoLAN.
- Nero's Recode2 makes use of the possibility of storing private streams in MP4 (question 4) and simply takes the DVD subpicture streams (vobsubs) from the DVD and stores them in MP4 without modifications
playback of these streams works with Nero's, Gabest's and Haali's Parser, VideoLAN and some Hardware MP4 DVD Players
- another way covered by the MPEG-4 Standard for storing subs in MP4 is to translate the subtitle format into the XMT/BT format and then to encode it as "advanced content" (BIFS binary format) in MP4. use mp4box or dvd2mp4gui for example to convert SRT subs
for playback of advanced content you need a filter/player that can handle this kind of content (see question 12)

8) How can i place Chapters in MP4 files?
chapters storage is possible by using advanced content (eg by creating a menu), but Nero uses a MP4 feature called "user space" (udta atom) which allows you to attach anything you want in MP4 (iTunes uses the udta atom for storing tags and cd/dvd-covers ("coverart") in MP4 for example).
atm you can place chapters in MP4 automatically during encoding with Nero Recode2 or, on existing files, with MP4Box and the MP4 directshow muxer filter coming with Recode2 (usable in graphedit)
As players, not knowing the info stored in udta, will simply ignore it, you need a player/filter that can handle this special chapters info (eg Gabest, Haali, Nero or 3ivx)

9) How can i author MP4 files (ie create DVD-like Menus)? Are there any samples?
basically the authoring has to be done "by hand" by using a textual language format, called XMT or bt (based on VRML, like the well known Flash), which than gets encoded/compiled into mp4 (free available encoders are mp4box, mp4tool or XMTBatch) as binary format (called BIFS)
There are already some GUI oriented MP4 authoring tools existing, which should make this process much easier, by IBM, AVIPIX, Envivio, Mindego, iVAST, Digimax or Etri, but all not available to the broad public

So if you want to try MP4 authoring yourself there is no way around writing an own BT/XMT script atm
thanks to the GPAC guys there is already a great Tutorial available in english and french, which can help you a lot with this
to make this process much easier i created a sample script, called MP4Menu, which already supports all features a DVD Menu offers and you will only have to adopt to your needs (guide)

if you want to know what for example can also be possible in MP4, check out this small in-video menu sample, but MPEG-4 Systems also offers things like animations in 2 and 3 Dimensions (think of movies like Toy Story or Finding Nemo), check out this small systems 2D animation sample (doesnt include a video stream!)
Make sure you use a Systems capable Player, like the GPAC Osmo4 player, to watch the samples

[bond]

10) How can I "anamorphic resize" with MP4?
As the MPEG-4 Standard aims to be a "multi-talent", satisfying everyone's needs, it offers 3 possibilites:
1) on the video bitstream level: maybe the most practicable and widely used method atm
use a codec which allows the setting of a PAR (eg 3ivx, ffmpeg/ffvfw, XviD), than mux the resulting AVI into MP4 by using any MP4 muxer (for example the 3ivx mp4 muxer, MP4Box or mp4UI). On already existing bitstreams you can change the PAR on MPEG-4 ASP with Moitah's MPEG4 Modifier, on AVC with hhanh's ARChange or on both formats with MP4Box
Anamorphic playback also already works automatically with VideoLAN, MPlayer or on DShow with the 3ivx, Nero or Haali parsers together with the XviD (set AR to auto), 3ivx (enable "force overlay"), Nero or ffdshow (enable "overlay mixer") decoder filter
2) on the container level: MP4 offers the possibility to use a "Composition Matrix", which allows the changing of the AR, rotating of the picture, multilayer handling, mixing of two audio streams during playback (eg seperated speech and music in movies)...
Quicktime/Pro already offers many composition possibilities via Movie -> Get Movie Properties -> Video/Sound Track -> Size/Layer/Volume/... and the correct playback of such composed MP4 files
3) on the BIFS level: which allows the broadest range of authoring possibilities (question 9) and therefore also changing of the AR (eg via Transform2D.scale)
for creating and playing with this BIFS control stream you can use the GPAC project tools: MP4Box and Osmo4

11) Is it possible to create Variable Framerate (VFR) content in MP4?
Yes, read the following threads for VFR with ASP and AVC

12) How can i play MP4 files?
as one of the big advantages of MP4 is interoperability and being an open standard (license free!) there already exist a lot of different tools supporting it on as good as all systems including Mac, Linux, PocketPC and of course Windows:

1) if you want to play any multimedia file in a directshow based player (for example media player classic, bsplayer, zoomplayer or the crappy windows media player) first of all two things are needed for playback:
- a splitter/parser filter, which splits up the container file into the included streams (audio, video, subtitles) during playback
- a decoder filter, which decodes the encoded streams (for example ffdshow, 3ivx, CoreAAC)
btw. the only reason why you don't have to install a splitter for AVI is that it is already installed on windows by default

there are some packages available, which include such filter:
- Gabest's MP4 Splitter supports AAC, ASP, AVC, MPEG-1/2 Audio (eg MP2/MP3) and Video, advanced TTXT, VobSubs and Chapters in MP4, opensource (Gabest's MPC player has this splitter inbuilt)
- Haali's Media Splitter supports AAC, ASP, AVC, MPEG-1/2 Audio (eg MP2/MP3) and Video, basic TTXT, VobSubs and Chapters in MP4, audio/video/subtitle streams switching, is unlimited, partly opensource and freely available
- 3ivx supports MP2, MP3, AAC, ASP, chapters but NOT AVC in MP4! For using it with alternative decoders like ffdshow or CoreAAC tick the "allow unsupported decoders" option
- Elecard offers a MP4 splitter able to handle AAC, ASP and AVC, together with ASP/AVC decoders
- Nero supports AAC, ASP, AVC, VobSubs and Chapters (works in Nero7 only in Nero Showtime! in Nero6 subs/chapters/multiple audio is limited to Showtime)
- HDX4 supports AAC and ASP in MP4
- EnvivioTV handles advanced content/BIFS (sample), AAC, ASP and AVC in MP4
- Moonlight offers a MP4 splitter able to handle MP3, AAC, ASP and AVC, together with ASP/AVC decoders
- Dicas' mpegable, supports RTP streaming, AAC, ASP and AMR (.3gp audio) decoding
- Ligos' LSX-MPEG, Simple Profile Video only, Demo limited to 30 days

2) if you can't/won't use windows-centric directshow you can also use one of the following players for playing MP4:
- Apple's Quicktime, widely used, supports MPEG-4 SP, AVC and AAC
- Realnetworks' RealPlayer 10, supports MPEG-4 SP + B-frames (only in the "plus" version) and AAC
- GPAC's Osmo4, opensource (GPL), able to decode BIFS (subtitles, user interactivity, dvd-like menus...) and TTXT
- MPlayer, opensource (GPL), handles ASP and AVC, available for various OSes, like Win, Linux, Mac OS...
- Videolan, opensource (GPL), handles ASP and AVC, various OSes supported
- MPEG4IP's WMP4Player, opensource (LGPL/MPL), handles ASP and AVC
- xine, opensource (GPL), various OSes supported
- TCPMP, available also for PalmOS/WindowsCE
- Philips' Platform4 Player, also offering a player for PocketPC
- ENST's Osmo4 (based on the reference source), able to decode advanced content/BIFS
- IBM's M4Play included in their Toolkit for MPEG-4, Java-based, able to decode advanced content/BIFS

3) hardware/standalone players: As the most popular MPEG-4 ASP implementations (DivX5/XviD) were often placed in AVI, thats the most widely supported format on hardware players atm. Still the guys from Nero, together with increasing consumer demand, try to push support for the MP4 container on hardware players, with increasing success:
MP4 enabled hardware players are:
- Avayon's DXP-1000 supports AAC, ASP, VobSubs and Chapters in MP4
- elta's 8815 MP4 supports AAC, ASP, VobSubs and Chapters in MP4
- Gowell's AS 602 supports AAC, ASP, VobSubs and Chapters in MP4
- Grundig's GDP 2550/3550/3560/3570/9550 supports AAC, ASP, VobSubs and Chapters in MP4
- KiSS's DP-558 supports AAC, ASP (no QPel/GMC), VobSubs and Chapters in MP4 (Sigma Designs EM8560)
- Packard Bell's DVD-DivX 450 pro supports AAC, ASP, VobSubs and Chapters in MP4
- Philips's DVP630/632/642 players support ASP (no QPel/1WP GMC) and MP3 audio (no AAC) in MP4 (ESS Vibratto-II)
- RJTech's RJ 1500DVX II supports AAC (5.1), MP3, ASP (QPel/1WP GMC/CQM), VobSubs, Chapters in MP4 (ESS Vibratto-II)
- Siemssen's SCO 5000 ND supports AAC (no MP3/MP2), ASP (QPel/1WP GMC), VobSubs, Chapters in MP4 (Zoran Vaddis 776)
- Targa's DR-5200x supports AAC, ASP, VobSubs and Chapters in MP4
- Tevion DR 2004, supports AAC, ASP (QPel/GMC?) and VobSubs in MP4
- Tevion DVD-4000, with latest firmware supports ASP (no QPel/1WP GMC?) and MP3 audio (no AAC) in MP4 (ESS Vibratto-II)
- Xoro's HSD 415/310 players supports AAC, ASP (no QPel/1WP GMC?), VobSubs, Chapters in MP4 (ESS Vibratto-II)
- M$'s Xbox with the Xbox Media Center is supposed to support MP2, MP3, AAC and AVC in MP4
- Sony's Playstation Portable (PSP) supports AAC, SP and AVC in MP4 from Memory Stick
- Apple's iPod supports AAC in MP4, iPod video supports additionally AVC in MP4
- Sigma Designs' Xcard handles hardware MPEG-4 decoding on PC including the MP4 container

13) How can i (live-)stream/play streamed MP4 files?
Apple and MPEG4IP offer nice and free tools when it comes to streaming MP4:
As streaming server you can use Apple's Darwin Streaming Server, Guides on the process are available from everwicked and linuxjournal
for live streaming you can use mp4live from MPEG4IP (only for Linux), Guides from everwicked and MPEG4IP; on Windows you can use MPEGRecorder (which seems to be a port of mp4live)
Also have a look at the tools from ViTooKi (opensource Streaming Server, Player and other tools)
Another free and opensource MP4 streaming server is available from Cata
for MAC you can have a look at Live Channel

To play broadcasted MP4 files you can use Apple's Quicktime, Real's RealPlayer 10, MPEG4IP's WMP4Player, Dicas' mpegable and EnvivioTV (both work in dshow players) and GPAC's Osmo4 (the last two also support streamed advanced content/user interactivitiy (interactive demo from Envivio)
also you can play streamed MP4 without the need to install a player (!) with the java applets from MediaFrame (demos) and IBM (interactive demos)

streaming samples: 1 2

14) Where can i find a MP4 bitrate calculator? Why are MP4 files created from AVI smaller than the source itself?
MP4 needs far less overhead than the AVI container (especially with VBR-MP3), no wonder cause in contrary to AVI the MP4 container was designed for storing MPEG-4 Video and MP3
As a rule of thumb you can say that the video AVI filesize = final audio+video MP4 size (like 700MB) - audio MP4 size + 3MB
3ivx also offers a MP4 bitrate calculator on their website, but it doesnt seem to be very accurate

15) Does MP4 support CRC/EDC or ECC?
No, the MP4 container itself doesnt handle this as the MPEG-4 standard expects the Error Detection/Correction to be placed in the bitstreams (where it belongs)
read more about Error Resilience in MPEG-4 bitstreams here

16) Is it possible to find out which codecs where used to create a MP4 file?
Yes, this is already possible for MPEG-4 ASP video streams and MP3 Audio streams (currently no real solution for AAC exists)
read more about it here

17) Is MP4 the successor of MP3?
Yes and No. No, because MP3 is one specific type of audio format, whereas MP4 is a container format and not an audio codec. Yes, because MP4 is part of the MPEG-4 Standard, which can be taken as the successor of the MPEG-1/2 standard, where MP3 was part of.
MPEG-4 also includes AAC, an audio codec better than MP3, which most of the time comes in the MP4 format

18) Is MP4 the same as MOV/3GP?
Apple's MOV container format was indeed taken as a starting point for MP4 (mainly the moov atom), but there are differences between them (eg AAC audio is stored differently in both).
MP4 on the other hand itself was the starting point for the development of the 3GP format (mainly for mobile phones), which has more in common with MP4 as MP4 with MOV for example, but still is a different format

19) I want to read more about MP4! Where can i find more infos?
there are a lot of infos availabe on the net:
the specs for MP4 are available here. a draft of the MPEG-4 Systems Standard can be found here
some documentation on MP4 is also available from here, here and here
there is also info on the homepage of the MPEG Industry Forum or the Motion Picture Experts Group (MPEG). FAQs are available about the MPEG-4 Standard or especially about MPEG-4 Systems (very technical)
other infos can be found on the audiocoding wiki (with a lot of info also about AAC)
Guides on MPEG4IP are available about MP4 creation, compiling issues or on their CVS Server
(thanks a lot to hans-j�rgen and ac-chan123 for these links)

cheers,
bond

[bond]

If you have any suggestions, ideas which questions to add to make the MP4 FAQ better or found any broken links, feel free to post below!
I will do my best to keep the FAQ up-to-date

Please don't use this sticky to discuss any MP4 issues, this thread is meant for info only!
If you have any questions plz search the forum, perhaps they already have been answered and only then start a new thread

thanks,
bond

[Kurtnoise13]

Is it also possible to place streams not covered by the MPEG-4 standard in MP4?
Yes, altough i dont like the idea of doing so, the MPEG-4 standard defines how to place any stream in MP4. Similar to how streams are marked in AVI with private FourCCs, in MP4 they get a "private track ID". Note that no player will be able to handle such streams in MP4, but will simply ignore them, if not explicitely specified to do so
the following streams, not covered by MPEG-4, can be placed in MP4 already:
.........
- DVD picture subtitles (Vobsubs), via Nero Recode2

You can also add Intervideo DVD Copy and probably some others dvd2ipod all-in-one. And for free, we have HandBrake...

[bond]

in what way do they use private streams? and are you sure that they dont simply write .mov files with the wrong extension

[Kurtnoise13]

a...good question but I can say that HandBrake uses mpeg4ip libs to mux and "burn" subtitles with the stream w/o haveving mov container reference.

For DVDCopy, I've seen (via GraphEdit) that it uses his own mp4 muxer and the files are decoded properly with Nero Showtime or Gabest/Haali mp4 splitter.

Dunno for others tools...

[bond]

so where are the private streams?

[Kurtnoise13]

well, in utda atom but...

[bond]

streams in udta??? how crappy is this ^^

can you upload such a sample plz

[Tuesday]

Q: Is it possible to stoe imformation about tracks, such as track title and language in .mp4?

an example would be labelling a track "Directors Comments" and setting the language of audio tracks.

I ask as i've been using matroska before and i assume these things are also possible in .mp4 but i cant find the place to do them in YAMB.

[Kurtnoise13]

@Tuesday: for Yamb, go to Options tab then check "View import Settings directly". At last, load your file and you will be able to add what you want in the trackname edit area.

@Bond: mooo, I completely missed your request. I'll upload some samples asap. Sorry.

[bond]

Tuesday: thx for the hint, i will add that question to the faq

[icpawc]

please does anyon know where to buy new mp4 1.5" screen i am in desperate need on on as i walked into a table and is smashed lol

it would be and amazing help

please reply

[Inventive Software]

Wrong thread. Start a new one.
@Bond: Time for a cleanup methinks.