The purpose of buffering is to accumulate enough data in a pipeline so that
playback can occur smoothly and without interruptions. It is typically done
-when reading from a (slow) and non-live network source but can also be used for
+when reading from a (slow) non-live network source but can also be used for
live sources.
We want to be able to implement the following features:
- caching of semi-live streams to a local, on disk, ringbuffer with seeking in
the cached area. This is similar to tivo-like timeshifting.
- progress report about the buffering operations
- - easy (backward compatible) application notification of buffering
- the possibility for the application to do more complex buffering
Some use cases:
the sinks.
- When the high watermark is hit, a BUFFERING message with 100% will be
posted, which instructs the application to continue playback.
- - When during playback, the low watermark is hit, the queue will start posting
+ - When the low watermark is hit during playback, the queue will start posting
BUFFERING messages again, making the application PAUSE the pipeline again
until the high watermark is hit again. This is called the rebuffering
stage.
- - during playback, the queue level will fluctuate between the high and the
- low watermark as a way to compensate for network irregularities.
+ - During playback, the queue level will fluctuate between the high and
+ low watermarks as a way to compensate for network irregularities.
This buffering method is usable when the demuxer operates in push mode.
Seeking in the stream requires the seek to happen in the network source.
- It is mostly desirable when the total duration of the file is not know, such
+ It is mostly desirable when the total duration of the file is not known, such
as in live streaming or when efficient seeking is not possible/required.
* Incremental download
file
In this case, we know the server is streaming a fixed length file to the
- client. The application can choose to download the file on disk. The buffer
+ client. The application can choose to download the file to disk. The buffer
element will provide a push or pull based srcpad to the demuxer to navigate in
the downloaded file.
This mode is only suitable when the client can determine the length of the
file on the server.
- In this case, buffering messages will be emited as usual when the requested
+ In this case, buffering messages will be emitted as usual when the requested
range is not within the downloaded area + buffersize. The buffering message
will also contain an indication that incremental download is being performed.
This flag can be used to let the application control the buffering in a more
This mode is suitable for all live streams.
- As with the incremental download mode, buffering messages are emited along
+ As with the incremental download mode, buffering messages are emitted along
with an indication that timeshifting download is in progress.
the playback elements. This latency can be introduced by a queue (such as a
jitterbuffer) or by other means (in the audiosink).
- Buffering messages can be emited in those live pipelines as well and serve as
+ Buffering messages can be emitted in those live pipelines as well and serve as
an indication to the user of the latency buffering. The application usually
does not react to these buffering messages with a state change.
~~~~~~~~
A GST_MESSAGE_BUFFERING must be posted on the bus when playback temporarily
-stops to buffer and when buffering finishes. When percentage field in the
+stops to buffer and when buffering finishes. When the percentage field in the
BUFFERING message is 100, buffering is done. Values less than 100 mean that
buffering is in progress.
"buffering-mode", GST_TYPE_BUFFERING_MODE,
enum { "stream", "download", "timeshift", "live" }
- - gives the buffering mode in use. See above for an explanation of the
- different modes of buffering. This field can be used to let the
+ - Buffering mode in use. See above for an explanation of the
+ different alternatives. This field can be used to let the
application have more control over the buffering process.
"avg-in-rate", G_TYPE_INT
- - gives the average input buffering speed in bytes/second. -1 is unknown.
+ - Average input buffering speed in bytes/second. -1 is unknown.
This is the average number of bytes per second that is received on the
buffering element input (sink) pads. It is a measurement of the network
speed in most cases.
"avg-out-rate", G_TYPE_INT
- - gives the average consumption speed in bytes/second. -1 is unknown.
+ - Average consumption speed in bytes/second. -1 is unknown.
This is the average number of bytes per second that is consumed by the
downstream element of the buffering element.
"buffering-left", G_TYPE_INT64
- - gives the estimated time that bufferring will take in milliseconds.
- -1 unknown.
+ - Estimated time that buffering will take in milliseconds. -1 is unknown.
This is measured based on the avg-in-rate and the filled level of the
queue. The application can use this hint to update the GUI about the
estimated remaining time that buffering will take.
Application
~~~~~~~~~~~
-While data is buffered, the pipeline should remain in the PAUSED state. It is
+While data is buffered the pipeline should remain in the PAUSED state. It is
also possible that more data should be buffered while the pipeline is PLAYING,
-in which case the pipeline should be PAUSED until the buffering finished.
+in which case the pipeline should be PAUSED until the buffering finishes.
BUFFERING messages can be posted while the pipeline is prerolling. The
application should not set the pipeline to PLAYING before a BUFFERING message
-with 100 percent value is received, which might only happen after the pipeline
-prerolled.
+with a 100 percent value is received, which might only happen after the pipeline
+prerolls.
An exception is made for live pipelines. The application may not change
the state of a live pipeline when a buffering message is received. Usually these
buffering messages contain the "buffering-mode" = "live".
-The buffering message can also instruct the application to switch to a periodical
-BUFFERING query instead to more precisely control the buffering process. The
-application can, for example, choose to not act on the BUFFERING message with
-100 percent fill level to resume playback but instead use the estimated download
-time to resume playback to get uninterrupted playback.
+The buffering message can also instruct the application to switch to a
+periodical BUFFERING query instead, so it can more precisely control the
+buffering process. The application can, for example, choose not to act on the
+BUFFERING complete message (buffer-percent = 100) to resume playback but use
+the estimated download time instead, resuming playback when it has determined
+that it should be able to provide uninterrupted playback.
Buffering Query
~~~~~~~~~~~~~~~
-In addition to the BUFFERING messages posted by the buffering elements we want
+In addition to the BUFFERING messages posted by the buffering elements, we want
to be able to query the same information from the application. We also want to
be able to present the user with information about the downloaded range in the
file so that the GUI can react on it.
In addition to all the fields present in the buffering message, the BUFFERING
-query contains the following field, which indicate the available downloaded
+query contains the following field, which indicates the available downloaded
range in a specific format and the estimated time to complete:
"busy", G_TYPE_BOOLEAN
- the format of the "start" and "stop" values below
"start", G_TYPE_INT64, -1 unknown
- - the start position of the available data
+ - the start position of the available data. If there are multiple ranges,
+ this field contains the start position of the currently downloading
+ range.
"stop", G_TYPE_INT64, -1 unknown
- - the stop position of the available data
+ - the stop position of the available data. If there are multiple ranges,
+ this field contains the stop position of the currently downloading
+ range.
"estimated-total", G_TYPE_INT64
- gives the estimated download time in milliseconds. -1 unknown.
When the size of the downloaded file is known, this value will contain
- the latest estimate of the remaining download time. This value is usualy
- only filled for the "download" buffering mode. The application can use
- this information to estimate the amount of remaining time to download the
- complete file.
+ the latest estimate of the remaining download time of the currently
+ downloading range. This value is usually only filled for the "download"
+ buffering mode. The application can use this information to estimate the
+ amount of remaining time to download till the end of the file.
+
+ "buffering-ranges", G_TYPE_ARRAY of GstQueryBufferingRange
+ - contains optionally the downloaded areas in the format given above. One
+ of the ranges contains the same start/stop position as above.
+
+ typedef struct
+ {
+ gint64 start;
+ gint64 stop;
+ } GstQueryBufferingRange;
+
For the "download" and "timeshift" buffering-modes, the start and stop positions
specify the ranges where efficient seeking in the downloaded media is possible.
"start" = 0
"stop" = the total filesize
"estimated-total" = 0
+ "buffering-ranges" = NULL
A GstBaseSrc in push mode replies to the BUFFERING query with:
"start" = current position
"stop" = current position
"estimated-total" = -1
+ "buffering-ranges" = NULL
Buffering strategies
projects / platform / upstream / gstreamer.git / blobdiff