There is a very large set of possible types that may be used to pass data between elements. Indeed, each new element that is defined may use a new data format (though unless at least one other element recognises that format, it will be most likely be useless since nothing will be able to link with it). In order for types to be useful, and for systems like autopluggers to work, it is necessary that all elements agree on the type definitions, and which properties are required for each type. The &GStreamer; framework itself simply provides the ability to define types and parameters, but does not fix the meaning of types and parameters, and does not enforce standards on the creation of new types. This is a matter for a policy to decide, not technical systems to enforce. For now, the policy is simple: Do not create a new type if you could use one which already exists. If creating a new type, discuss it first with the other &GStreamer; developers, on at least one of: IRC, mailing lists. Try to ensure that the name for a new format is as unlikely to conflict with anything else created already, and is not a more generalised name than it should be. For example: "audio/compressed" would be too generalised a name to represent audio data compressed with an mp3 codec. Instead "audio/mp3" might be an appropriate name, or "audio/compressed" could exist and have a property indicating the type of compression used. Ensure that, when you do create a new type, you specify it clearly, and get it added to the list of known types so that other developers can use the type correctly when writing their elements. If you need a new format that has not yet been defined in our , you will want to have some general guidelines on media type naming, properties and such. A media type would ideally be equivalent to the Mime-type defined by IANA; else, it should be in the form type/x-name, where type is the sort of data this media type handles (audio, video, ...) and name should be something specific for this specific type. Audio and video media types should try to support the general audio/video properties (see the list), and can use their own properties, too. To get an idea of what properties we think are useful, see (again) the list. Take your time to find the right set of properties for your type. There is no reason to hurry. Also, experimenting with this is generally a good idea. Experience learns that theoretically thought-out types are good, but they still need practical use to assure that they serve their needs. Make sure that your property names do not clash with similar properties used in other types. If they match, make sure they mean the same thing; properties with different types but the same names are not allowed. With only defining the types, we're not yet there. In order for a random data file to be recognized and played back as such, we need a way of recognizing their type out of the blue. For this purpose, typefinding was introduced. Typefinding is the process of detecting the type of a data stream. Typefinding consists of two separate parts: first, there's an unlimited number of functions that we call typefind functions, which are each able to recognize one or more types from an input stream. Then, secondly, there's a small engine which registers and calls each of those functions. This is the typefind core. On top of this typefind core, you would normally write an autoplugger, which is able to use this type detection system to dynamically build a pipeline around an input stream. Here, we will focus only on typefind functions. A typefind function usually lives in gst-plugins-base/gst/typefind/gsttypefindfunctions.c, unless there's a good reason (like library dependencies) to put it elsewhere. The reason for this centralization is to reduce the number of plugins that need to be loaded in order to detect a stream's type. Below is an example that will recognize AVI files, which start with a RIFF tag, then the size of the file and then an AVI tag: static void gst_my_typefind_function (GstTypeFind *tf, gpointer data) { guint8 *data = gst_type_find_peek (tf, 0, 12); if (data && GUINT32_FROM_LE (&((guint32 *) data)[0]) == GST_MAKE_FOURCC ('R','I','F','F') && GUINT32_FROM_LE (&((guint32 *) data)[2]) == GST_MAKE_FOURCC ('A','V','I',' ')) { gst_type_find_suggest (tf, GST_TYPE_FIND_MAXIMUM, gst_caps_new_simple ("video/x-msvideo", NULL)); } } static gboolean plugin_init (GstPlugin *plugin) { static gchar *exts[] = { "avi", NULL }; if (!gst_type_find_register (plugin, "", GST_RANK_PRIMARY, gst_my_typefind_function, exts, gst_caps_new_simple ("video/x-msvideo", NULL), NULL)) return FALSE; } Note that gst-plugins/gst/typefind/gsttypefindfunctions.c has some simplification macros to decrease the amount of code. Make good use of those if you want to submit typefinding patches with new typefind functions. Autoplugging has been discussed in great detail in the Application Development Manual. Below is a list of all the defined types in &GStreamer;. They are split up in separate tables for audio, video, container, subtitle and other types, for the sake of readability. Below each table might follow a list of notes that apply to that table. In the definition of each type, we try to follow the types and rules as defined by IANA for as far as possible. Jump directly to a specific table: Note that many of the properties are not required, but rather optional properties. This means that most of these properties can be extracted from the container header, but that - in case the container header does not provide these - they can also be extracted by parsing the stream header or the stream content. The policy is that your element should provide the data that it knows about by only parsing its own content, not another element's content. Example: the AVI header provides samplerate of the contained audio stream in the header. MPEG system streams don't. This means that an AVI stream demuxer would provide samplerate as a property for MPEG audio streams, whereas an MPEG demuxer would not. A decoder needing this data would require a stream parser in between two extract this from the header or calculate it from the stream. Media Type Description Property Property Type Property Values Property Description All audio types. audio/* All audio types rate integer greater than 0 The sample rate of the data, in samples (per channel) per second. channels integer greater than 0 The number of channels of audio data. channel-mask bitmask Channel positions present. See GstAudioChannelPosition. 0 means unpositioned. format string S8 U8 S16LE S16BE U16LE U16BE S24_32LE S24_32BE U24_32LE U24_32BE S32LE S32BE U32LE U32BE S24LE S24BE U24LE U24BE S20LE S20BE U20LE U20BE S18LE S18BE U18LE U18BE F32LE F32BE F64LE F64BE The format of the sample data. layout string "interleaved" or "non-interleaved" Layout of channels within a buffer. All raw audio types. audio/x-raw Unstructured and uncompressed raw audio data. All properties (except channel-mask, in the mono and stereo cases) are mandatory. All encoded audio types. audio/x-ac3 AC-3 or A52 audio streams. There are currently no specific properties defined or needed for this type. audio/x-adpcm ADPCM Audio streams. layout string quicktime, dvi, microsoft or 4xm. The layout defines the packing of the samples in the stream. In ADPCM, most formats store multiple samples per channel together. This number of samples differs per format, hence the different layouts. On the long term, we probably want this variable to die and use something more descriptive, but this will do for now. block_align integer Any Chunk buffer size. audio/x-cinepak Audio as provided in a Cinepak (Quicktime) stream. There are currently no specific properties defined or needed for this type. audio/x-dv Audio as provided in a Digital Video stream. There are currently no specific properties defined or needed for this type. audio/x-flac Free Lossless Audio codec (FLAC). There are currently no specific properties defined or needed for this type. audio/x-gsm Data encoded by the GSM codec. There are currently no specific properties defined or needed for this type. audio/x-alaw A-Law Audio. There are currently no specific properties defined or needed for this type. audio/x-mulaw Mu-Law Audio. There are currently no specific properties defined or needed for this type. audio/x-mace MACE Audio (used in Quicktime). maceversion integer 3 or 6 The version of the MACE audio codec used to encode the stream. audio/mpeg Audio data compressed using the MPEG audio encoding scheme. mpegversion integer 1, 2 or 4 The MPEG-version used for encoding the data. The value 1 refers to MPEG-1, -2 and -2.5 layer 1, 2 or 3. The values 2 and 4 refer to the MPEG-AAC audio encoding schemes. framed boolean 0 or 1 A true value indicates that each buffer contains exactly one frame. A false value indicates that frames and buffers do not necessarily match up. layer integer 1, 2, or 3 The compression scheme layer used to compress the data (only if mpegversion=1). bitrate integer greater than 0 The bitrate, in bits per second. For VBR (variable bitrate) MPEG data, this is the average bitrate. audio/x-qdm2 Data encoded by the QDM version 2 codec. There are currently no specific properties defined or needed for this type. audio/x-pn-realaudio Realmedia Audio data. raversion integer 1 or 2 The version of the Real Audio codec used to encode the stream. 1 stands for a 14k4 stream, 2 stands for a 28k8 stream. audio/x-speex Data encoded by the Speex audio codec There are currently no specific properties defined or needed for this type. audio/x-vorbis Vorbis audio data There are currently no specific properties defined or needed for this type. audio/x-wma Windows Media Audio wmaversion integer 1,2 or 3 The version of the WMA codec used to encode the stream. audio/x-paris Ensoniq PARIS audio There are currently no specific properties defined or needed for this type. audio/x-svx Amiga IFF / SVX8 / SV16 audio There are currently no specific properties defined or needed for this type. audio/x-nist Sphere NIST audio There are currently no specific properties defined or needed for this type. audio/x-voc Sound Blaster VOC audio There are currently no specific properties defined or needed for this type. audio/x-ircam Berkeley/IRCAM/CARL audio There are currently no specific properties defined or needed for this type. audio/x-w64 Sonic Foundry's 64 bit RIFF/WAV There are currently no specific properties defined or needed for this type. Media Type Description Property Property Type Property Values Property Description All video types. video/* All video types width integer greater than 0 The width of the video image height integer greater than 0 The height of the video image framerate fraction greater or equal 0; default 0/1 The (average) framerate in frames per second. Note that this property does not guarantee in any way that it will actually come close to this value. If you need a fixed framerate, please use an element that provides that (such as videorate). 0/1 means a variable framerate. max-framerate fraction greater or equal 0; default as framerate For variable framerates, the maximum framerate that is expected. Only valid when framerate is 0/1. views integer greater than 0; default 1 The number of views for multiview video. Each buffer contains multiple GstVideoMeta buffers that describe each view. Use the frame ID to get access to the different views. interlace-mode string progressive, interleaved, mixed, fields; default progressive The interlace mode. Extra buffer flags describe the frame and fields. chroma-site string jpeg, mpeg2, dv; default UNKNOWN The chroma siting of the video frames. colorimetry string bt601, bt709, smpte240m; default UNKNOWN The colorimetry of the video frames. pixel-aspect-ratio fraction greater than 0; default 1/1 The pixel aspect ratio of the video. format string I420 YV12 YUY2 UYVY AYUV RGBx BGRx xRGB xBGR RGBA BGRA ARGB ABGR RGB BGR Y41B Y42B YVYU Y444 v210 v216 NV12 NV21 GRAY8 GRAY16_BE GRAY16_LE v308 RGB16 BGR16 RGB15 BGR15 UYVP A420 RGB8P YUV9 YVU9 IYU1 ARGB64 AYUV64 r210 I420_10LE I420_10BE I422_10LE I422_10BE The format of the video. See FourCC definition site for references and definitions. YUY2, YVYU and UYVY are 4:2:2 packed-pixel, Y41P is 4:1:1 packed-pixel and IYU2 is 4:4:4 packed-pixel. Y42B is 4:2:2 planar, YV12 and I420 are 4:2:0 planar, Y41B is 4:1:1 planar and YUV9 and YVU9 are 4:1:0 planar. Y800 contains Y-samples only (black/white). All raw video types. video/x-raw Unstructured and uncompressed raw video data. The properties width, height and format are mandatory. All encoded video types. video/x-3ivx 3ivx video. There are currently no specific properties defined or needed for this type. video/x-divx DivX video. divxversion integer 3, 4 or 5 Version of the DivX codec used to encode the stream. video/x-dv Digital Video. systemstream boolean FALSE Indicates that this stream is not a system container stream. video/x-ffv FFMpeg video. ffvversion integer 1 Version of the FFMpeg video codec used to encode the stream. video/x-h263 H-263 video. variant string itu, lead, microsoft, vdolive, vivo, xirlink Vendor specific variant of the format. 'itu' is the standard. h263version string h263, h263p, h263pp Enhanced versions of the h263 codec. video/x-h264 H-264 video. variant string itu, videosoft Vendor specific variant of the format. 'itu' is the standard. video/x-huffyuv Huffyuv video. There are currently no specific properties defined or needed for this type. video/x-indeo Indeo video. indeoversion integer 3 Version of the Indeo codec used to encode this stream. video/x-intel-h263 H-263 video. variant string intel Vendor specific variant of the format. video/x-jpeg Motion-JPEG video. There are currently no specific properties defined or needed for this type. Note that video/x-jpeg only applies to Motion-JPEG pictures (YUY2 colourspace). RGB colourspace JPEG images are referred to as image/jpeg (JPEG image). video/mpeg MPEG video. mpegversion integer 1, 2 or 4 Version of the MPEG codec that this stream was encoded with. Note that we have different media types for 3ivx, XviD, DivX and "standard" ISO MPEG-4. This is not a good thing and we're fully aware of this. However, we do not have a solution yet. systemstream boolean FALSE Indicates that this stream is not a system container stream. video/x-msmpeg Microsoft MPEG-4 video deviations. msmpegversion integer 41, 42 or 43 Version of the MS-MPEG-4-like codec that was used to encode this version. A value of 41 refers to MS MPEG 4.1, 42 to 4.2 and 43 to version 4.3. video/x-msvideocodec Microsoft Video 1 (oldish codec). msvideoversion integer 1 Version of the codec - always 1. video/x-pn-realvideo Realmedia video. rmversion integer 1, 2 or 3 Version of the Real Video codec that this stream was encoded with. video/x-rle RLE animation format. layout string "microsoft" or "quicktime" The RLE format inside the Microsoft AVI container has a different byte layout than the RLE format inside Apple's Quicktime container; this property keeps track of the layout. depth integer 1 to 64 Bit depth of the used palette. This means that the palette that belongs to this format defines 2^depth colors. palette_data GstBuffer Buffer containing a color palette (in native-endian RGBA) used by this format. The buffer is of size 4*2^depth. video/x-svq Sorensen Video. svqversion integer 1 or 3 Version of the Sorensen codec that the stream was encoded with. video/x-tarkin Tarkin video. There are currently no specific properties defined or needed for this type. video/x-theora Theora video. There are currently no specific properties defined or needed for this type. video/x-vp3 VP-3 video. There are currently no specific properties defined or needed for this type. Note that we have different media types for VP-3 and Theora, which is not necessarily a good idea. This could probably be improved. video/x-wmv Windows Media Video wmvversion integer 1,2 or 3 Version of the WMV codec that the stream was encoded with. video/x-xvid XviD video. There are currently no specific properties defined or needed for this type. All image types. image/gif Graphics Interchange Format. There are currently no specific properties defined or needed for this type. image/jpeg Joint Picture Expert Group Image. There are currently no specific properties defined or needed for this type. Note that image/jpeg only applies to RGB-colourspace JPEG images; YUY2-colourspace JPEG pictures are referred to as video/x-jpeg ("Motion JPEG"). image/png Portable Network Graphics Image. There are currently no specific properties defined or needed for this type. image/tiff Tagged Image File Format. There are currently no specific properties defined or needed for this type. Media Type Description Property Property Type Property Values Property Description video/x-ms-asf Advanced Streaming Format (ASF). There are currently no specific properties defined or needed for this type. video/x-msvideo AVI. There are currently no specific properties defined or needed for this type. video/x-dv Digital Video. systemstream boolean TRUE Indicates that this is a container system stream rather than an elementary video stream. video/x-matroska Matroska. There are currently no specific properties defined or needed for this type. video/mpeg Motion Pictures Expert Group System Stream. systemstream boolean TRUE Indicates that this is a container system stream rather than an elementary video stream. application/ogg Ogg. There are currently no specific properties defined or needed for this type. video/quicktime Quicktime. There are currently no specific properties defined or needed for this type. application/vnd.rn-realmedia RealMedia. There are currently no specific properties defined or needed for this type. audio/x-wav WAV. There are currently no specific properties defined or needed for this type. Media Type Description Property Property Type Property Values Property Description None defined yet. Media Type Description Property Property Type Property Values Property Description None defined yet.