mirror of
https://gitlab.freedesktop.org/gstreamer/gstreamer.git
synced 2024-11-30 21:51:09 +00:00
71 lines
2.5 KiB
Markdown
71 lines
2.5 KiB
Markdown
# Query
|
|
|
|
## Purpose
|
|
|
|
Queries are used to get information about the stream. A query is started
|
|
on a specific pad and travels up or downstream.
|
|
|
|
## Requirements
|
|
|
|
- multiple return values, grouped together when they make sense.
|
|
|
|
- one pad function to perform the query
|
|
|
|
- extensible queries.
|
|
|
|
## Implementation
|
|
|
|
- `GstQuery` extends `GstMiniObject` and contains a `GstStructure` (see
|
|
`GstMessage`)
|
|
|
|
- some standard query types are defined below
|
|
|
|
- methods to create and parse the results in the `GstQuery`.
|
|
|
|
- define pad
|
|
method:
|
|
|
|
``` c
|
|
gboolean (*GstPadQueryFunction) (GstPad *pad,
|
|
GstObject *parent,
|
|
GstQuery *query);
|
|
```
|
|
|
|
pad returns result in query structure and TRUE as result or FALSE when query is
|
|
not supported.
|
|
|
|
## Query types
|
|
|
|
**`GST_QUERY_POSITION`**: get info on current position of the stream in `stream_time`.
|
|
|
|
**`GST_QUERY_DURATION`**: get info on the total duration of the stream.
|
|
|
|
**`GST_QUERY_LATENCY`**: get amount of latency introduced in the pipeline. (See [latency](additional/design/latency.md))
|
|
|
|
**`GST_QUERY_RATE`**: get the current playback rate of the pipeline
|
|
|
|
**`GST_QUERY_SEEKING`**: get info on how seeking can be done
|
|
- getrange, with/without offset/size
|
|
- ranges where seeking is efficient (for caching network sources)
|
|
- flags describing seeking behaviour (forward, backward, segments,
|
|
play backwards, ...)
|
|
|
|
**`GST_QUERY_SEGMENT`**: get info about the currently configured playback segment.
|
|
|
|
**`GST_QUERY_CONVERT`**: convert format/value to another format/value pair.
|
|
|
|
**`GST_QUERY_FORMATS`**: return list of supported formats that can be used for `GST_QUERY_CONVERT`.
|
|
|
|
**`GST_QUERY_BUFFERING`**: query available media for efficient seeking (See [buffering](additional/design/buffering.md))
|
|
|
|
**`GST_QUERY_CUSTOM`**: a custom query, the name of the query defines the properties of the query.
|
|
|
|
**`GST_QUERY_URI`**: query the uri of the source or sink element
|
|
|
|
**`GST_QUERY_ALLOCATION`**: the buffer allocation properties (See [bufferpool](additional/design/bufferpool.md))
|
|
|
|
**`GST_QUERY_SCHEDULING`**: the scheduling properties (See [scheduling](additional/design/scheduling.md))
|
|
|
|
**`GST_QUERY_ACCEPT_CAPS`**: check if caps are supported (See [negotiation](additional/design/negotiation.md))
|
|
|
|
**`GST_QUERY_CAPS`**: get the possible caps (See [negotiation](additional/design/negotiation.md))
|