6.1. Video formats

6.1. Video formats

6.1.1. MPEG files

MPEG files come in different guises:

• MPG: This is the most basic form of the MPEG file formats. It contains MPEG-1 video, and MP2 (MPEG-1 layer 2) or rarely MP1 audio.

• DAT: This is the very same format as MPG with a different extension. It is used on Video CDs. Due to the way VCDs are created and linux is designed, the DAT files cannot be played nor copied from VCDs as regular files. You have to use vcd:// to play a Video CD.

• VOB: This is the MPEG file format on DVDs. It is the same as MPG, plus the capability to contain subtitles or non-MPEG (AC-3) audio. It contains encoded MPEG-2 video and usually AC-3 audio, but DTS, MP2 and uncompressed LPCM are allowed, too. Read the DVD section!

• TY: This is a TiVo MPEG stream. It contains MPEG PES data for audio and video streams, as well as extra information like closed captions. The container is not an MPEG program stream, but a closed format created by TiVo. For more information on TiVo stream format, please refer to the TyStudio page.

Series of frames form independent groups in MPEG files. This means that you can cut/join an MPEG file with standard file tools (like dd, cut), and it remains completely functional.

One important feature of MPEG files is that they have a field to describe the aspect ratio of the video stream within. For example SVCDs have 480x480 resolution video, and in the header that field is set to 4:3, so that it is played at 640x480. AVI files often lack this field, so they have to be rescaled during encoding or played with the -aspect option.

6.1.2. AVI files

Designed by Microsoft, AVI (Audio Video Interleaved) is a widespread multipurpose format currently used mostly for MPEG-4 (DivX and DivX4) video. It has many known drawbacks and shortcomings (for example in streaming). It supports one video stream and 0 to 99 audio streams and can be as big as 2GB, but there exists an extension allowing bigger files called OpenDML. microsoft currently strongly discourages its use and encourages ASF/WMV. Not that anybody cares.

There is a hack that allows AVI files to contain an Ogg Vorbis audio stream, but makes them incompatible with standard AVI. MPlayer supports playing these files. Seeking is also implemented but severely hampered by badly encoded files with confusing headers. Unfortunately the only encoder currently capable of creating these files, NanDub, has this problem.

Note

DV cameras create raw DV streams that DV grabbing utilities convert to two different types of AVI files. The AVI will then contain either separate audio and video streams that MPlayer can play or the raw DV stream for which support is under development.

There are two kinds of AVI files:

• Interleaved: audio and video content is interleaved. This is the standard usage. Recommended and mostly used. Some tools create interleaved AVIs with bad sync. MPlayer detects these as interleaved, and this climaxes in loss of A/V sync, probably at seeking. These files should be played as non-interleaved (with the -ni option).

• Non-interleaved: First comes the whole video stream, then the whole audio stream. It thus needs a lot of seeking, making playing from network or CD-ROM difficult.

MPlayer supports two kinds of timings for AVI files:

• bps-based: It is based on the bitrate/samplerate of the video/audio stream. This method is used by most players, including avifile and Windows Media Player. Files with broken headers, and files created with VBR audio but not VBR-compliant encoder will result in A/V desync with this method (mostly at seeking).

• interleaving-based: It does not use the bit-rate value of the header, instead it uses the relative position of interleaved audio and video chunks, making badly encoded files with VBR audio playable.

Any audio and video codec is allowed, but note that VBR audio is not well supported by most players. The file format makes it possible to use VBR audio, but most players expect CBR audio, thus they fail with VBR. VBR is uncommon and Microsoft's AVI specs only describe CBR audio. I also noticed that most AVI encoders/multiplexers create bad files when using VBR audio. There are only two known exceptions: NanDub and MEncoder.

6.1.3. ASF/WMV files

ASF (Active Streaming Format) comes from Microsoft. They developed two variants of ASF, v1.0 and v2.0. v1.0 is used by their media tools (Windows Media Player and Windows Media Encoder) and is very secret. v2.0 is published and patented :). Of course they differ, there is no compatibility at all (it is just another legal game). MPlayer supports only v1.0, as nobody has ever seen v2.0 files :). Note that ASF files nowadays come with the extension .WMA or .WMV.

6.1.4. QuickTime/MOV files

These formats were designed by Apple and can contain any codec, CBR or VBR. They usually have a .QT or .MOV extension. Note that since the MPEG-4 group chose QuickTime as the recommended file format for MPEG-4, their MOV files come with a .MPG or .MP4 extension (Interestingly the video and audio streams in these files are real MPG and AAC files. You can even extract them with the -dumpvideo and -dumpaudio options.).

6.1.5. VIVO files

MPlayer happily demuxes VIVO file formats. The biggest disadvantage of the format is that it has no index block, nor a fixed packet size or sync bytes and most files lack even keyframes, so forget seeking!

The video codec of VIVO/1.0 files is standard h.263. The video codec of VIVO/2.0 files is a modified, nonstandard h.263v2. The audio is the same, it may be g.723 (standard), or Vivo Siren.

6.1.6. FLI files

FLI is a very old file format used by Autodesk Animator, but it is a common file format for short animations on the net. MPlayer demuxes and decodes FLI movies and is even able to seek within them (useful when looping with the -loop option). FLI files do not have keyframes, so the picture will be messy for a short time after seeking.

6.1.7. RealMedia (RM) files

Yes, MPlayer can read (demux) RealMedia (.rm) files.

6.1.8. NuppelVideo files

NuppelVideo is a TV grabber tool (AFAIK:). MPlayer can read its .NUV files (only NuppelVideo 5.0). Those files can contain uncompressed YV12, YV12+RTJpeg compressed, YV12 RTJpeg+lzo compressed, and YV12+lzo compressed frames. MPlayer decodes (and also encodes them with MEncoder to MPEG-4 (DivX)/etc!) them all. Seeking works.

6.1.9. yuv4mpeg files

yuv4mpeg / yuv4mpeg2 is a file format used by the mjpegtools programs. You can grab, produce, filter or encode video in this format using these tools. The file format is really a sequence of uncompressed YUV 4:2:0 images.

6.1.10. FILM files

This format is used on old Sega Saturn CD-ROM games.

6.1.11. RoQ files

RoQ files are multimedia files used in some ID games such as Quake III and Return to Castle Wolfenstein.

6.1.12. OGG/OGM files

This is a new file format from the Xiph.Org Foundation. It can contain any video or audio codec, CBR or VBR. You'll need libogg and libvorbis installed before compiling MPlayer to be able to play it.

6.1.13. SDP files

SDP is an IETF standard format for describing video and/or audio RTP streams. (The "LIVE555 Streaming Media" are required.)

6.1.14. PVA files

PVA is an MPEG-like format used by DVB TV boards' software (e.g.: MultiDec, WinTV under Windows).

6.1.15. NSV files

NSV (NullSoft Video) is the file format used by the Winamp player to stream audio and video. Video is VP3, VP5 or VP6, audio is MP3, AAC or VLB. The audio only version of NSV has the .nsa extension. MPlayer can play both NSV streams and files. Please note that most files from the Winamp site use VLB audio, that can't be decoded yet. Moreover streams from that site need an extra depacketization layer that still has to be implemented (those files are unplayable anyway because they use VLB audio).

6.1.16. Matroska files

Matroska is an open container format. Read more on the official site.

6.1.17. NUT files

NUT is the container format developed by MPlayer and FFmpeg folks. Both projects support it. Read more on the official site.

6.1.18. GIF files

The GIF format is a common format for web graphics. There are two versions of the GIF spec, GIF87a and GIF89a. The main difference is that GIF89a allows for animation. MPlayer supports both formats through use of libungif or another libgif-compatible library. Non-animated GIFs will be displayed as single frame videos. (Use the -loop and -fixed-vo options to display these longer.)

MPlayer currently does not support seeking in GIF files. GIF files do not necessarily have a fixed frame size, nor a fixed framerate. Rather, each frame is of independent size and is supposed to be positioned in a certain place on a field of fixed-size. The framerate is controlled by an optional block before each frame that specifies the next frame's delay in centiseconds.

Standard GIF files contain 24-bit RGB frames with at most an 8-bit indexed palette. These frames are usually LZW-compressed, although some GIF encoders produce uncompressed frames to avoid patent issues with LZW compression.

If your distribution does not come with libungif, download a copy from the libungif homepage. For detailed technical information, have a look at the GIF89a specification.