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design: stream-selection: missing markup and formatting fixes

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Reynaldo H. Verdejo Pinochet 2017-06-02 14:57:45 -07:00
parent 8084a45563
commit b3b501e183
1 changed files with 23 additions and 20 deletions
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43
markdown/design/stream-selection.md
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@ -99,13 +99,14 @@ Stream selection in GStreamer is implemented in several parts:
## GstStream objects
```
API:
```
GstStream
gst_stream_new(..)
gst_stream_get_\*(...)
gst_stream_set_\*()
gst_stream_new(...)
gst_stream_get_*(...)
gst_stream_set_*(...)
gst_event_set_stream(...)
gst_event_parse_stream(...)
```
@ -130,16 +131,17 @@ The various properties of a `GstStream` object are:
elements already using the notion of stream (which is common for
example in demuxers).
Elements that create GstStream should also set it on the
Elements that create `GstStream` should also set it on the
`GST_EVENT_STREAM_START` event of the relevant pad. This helps
downstream elements to have all information in one location.
## Exposing collections of streams
```
API:
```
GstStreamCollection
gst_stream_collection_new(...)
gst_stream_collection_add_stream(...)
gst_stream_collection_get_size(...)
@ -154,7 +156,7 @@ gst_event_parse_stream_collection(...)
Elements that create new streams (such as demuxers) or can create
new streams (like the HLS/DASH alternative streams) can list the
streams they can make available with the GstStreamCollection object.
streams they can make available with the `GstStreamCollection` object.
Other elements that might generate `GstStreamCollections` are the
DVD-VM, which handles internal switching of tracks, or parsebin and
@ -202,11 +204,11 @@ referencing problems.
### Usage from elements
When a demuxer knows the list of streams it can expose, it
creates a new GstStream for each stream it can provide with the
creates a new `GstStream` for each stream it can provide with the
appropriate information (stream id, flag, tags, caps, ...).
The demuxer then creates a GstStreamCollection object in which it
will put the list of GstStream it can expose. That collection is
The demuxer then creates a `GstStreamCollection` object in which it
will put the list of `GstStream` it can expose. That collection is
then both posted on the bus (via a `GST_MESSAGE_COLLECTION`) and on
each pad (via a `GST_EVENT_STREAM_COLLECTION`).
@ -244,9 +246,10 @@ element even if it doesn't implement the `GstStreamCollection` usage.
## Stream selection event
```
API:
```
GST_EVENT_SELECT_STREAMS
gst_event_new_select_streams(...)
gst_event_parse_select_streams(...)
@ -315,7 +318,7 @@ pre-roll before a pipeline is completely linked down to sinks.
This is an example of how decodebin3 works by using the
above-mentioned objects/events/messages.
For clarity/completeness, we will consider a mpeg-ts stream that has
For clarity/completeness, we will consider a MPEG-TS stream that has
multiple audio streams. Furthermore that stream might have changes
at some point (switching video codec, or adding/removing audio
streams).
@ -462,10 +465,10 @@ through the same pad as the previous video stream in a gapless fashion.
##### HLS alternates
There is a main (multi-bitrate or not) stream with audio and
video interleaved in mpeg-ts. The manifest also indicates the
video interleaved in MPEG-TS. The manifest also indicates the
presence of alternate language audio-only streams.
HLS would expose one collection containing:
1) The main A+V CONTAINER stream (mpeg-ts), initially active,
1) The main A+V CONTAINER stream (MPEG-TS), initially active,
downloaded and exposed as a pad
2) The alternate A-only streams, initially inactive and not exposed as pads
the tsdemux element connected to the first stream will also expose
@ -504,7 +507,7 @@ default english one.
#### multi-program MPEG-TS
Assuming the case of a mpeg-ts stream which contains multiple
Assuming the case of a MPEG-TS stream which contains multiple
programs.
There would be three "levels" of collection:
1) The collection of programs presents in the stream
@ -570,17 +573,17 @@ another or not.
### OPEN QUESTIONS
- Is a `FLUSHING` flag for stream-selection required or not ? This would
- Is a `FLUSHING` flag for stream-selection required or not? This would
make the handler of the `SELECT_STREAMS` event send `FLUSH START/STOP`
before switching to the other streams. This is tricky when dealing
where situations where we keep some streams and only switch some
others. Do we flush all streams ? Do we only flush the new streams,
potentially resulting in delay to fully switch ? Furthermore, due to
others. Do we flush all streams? Do we only flush the new streams,
potentially resulting in delay to fully switch? Furthermore, due to
efficient buffering in decodebin3, the switching time has been
minimized extensively, to the point where flushing might not bring a
noticeable improvement.
- Store the stream collection in bins/pipelines ? A Bin/Pipeline could
- Store the stream collection in bins/pipelines? A Bin/Pipeline could
store all active collection internally, so that it could be queried
later on. This could be useful to then get, on any pipeline, at any
point in time, the full list of collections available without having
@ -591,4 +594,4 @@ fixing the "is a collection a replacement or not" issue first.
to *map* corresponding streams from the old to new PMT - that is,
try and stick to the *english* language audio track, for example?
Alternatively, rely on the app to do such smarts with stream-select
messages ?
messages?