Commit a1c32761 authored by Thiago Santos's avatar Thiago Santos

videodecoder: documentation cleanup

Remove some whitespace and break lines longer than 80 columns
parent 30e9c26b
......@@ -25,12 +25,13 @@
/**
* SECTION:gstvideodecoder
* @short_description: Base class for video decoders
* @see_also:
* @see_also:
*
* This base class is for video decoders turning encoded data into raw video
* frames.
*
* The GstVideoDecoder base class and derived subclasses should cooperate as follows:
* The GstVideoDecoder base class and derived subclasses should cooperate as
* follows:
* <orderedlist>
* <listitem>
* <itemizedlist><title>Configuration</title>
......@@ -46,7 +47,8 @@
* parameters require reconfiguration.
* </para></listitem>
* <listitem><para>
* Incoming data buffers are processed as needed, described in Data Processing below.
* Incoming data buffers are processed as needed, described in Data
* Processing below.
* </para></listitem>
* <listitem><para>
* GstVideoDecoder calls @stop at end of all processing.
......@@ -62,15 +64,17 @@
* corresponding to and referred to as 'frames'.
* </para></listitem>
* <listitem><para>
* Each input frame is provided in turn to the subclass' @handle_frame callback.
* Each input frame is provided in turn to the subclass' @handle_frame
* callback.
* The ownership of the frame is given to the @handle_frame callback.
* </para></listitem>
* <listitem><para>
* If codec processing results in decoded data, the subclass should call
* @gst_video_decoder_finish_frame to have decoded data pushed.
* downstream. Otherwise, the subclass must call @gst_video_decoder_drop_frame, to
* allow the base class to do timestamp and offset tracking, and possibly to
* requeue the frame for a later attempt in the case of reverse playback.
* downstream. Otherwise, the subclass must call
* @gst_video_decoder_drop_frame, to allow the base class to do timestamp
* and offset tracking, and possibly to requeue the frame for a later
* attempt in the case of reverse playback.
* </para></listitem>
* </itemizedlist>
* </listitem>
......@@ -87,20 +91,21 @@
* <listitem>
* <itemizedlist><title>Seeking/Flushing</title>
* <listitem><para>
* When the pipeline is seeked or otherwise flushed, the subclass is informed via a call
* to its @reset callback, with the hard parameter set to true. This indicates the
* subclass should drop any internal data queues and timestamps and prepare for a fresh
* set of buffers to arrive for parsing and decoding.
* When the pipeline is seeked or otherwise flushed, the subclass is
* informed via a call to its @reset callback, with the hard parameter
* set to true. This indicates the subclass should drop any internal data
* queues and timestamps and prepare for a fresh set of buffers to arrive
* for parsing and decoding.
* </para></listitem>
* </itemizedlist>
* </listitem>
* <listitem>
* <itemizedlist><title>End Of Stream</title>
* <listitem><para>
* At end-of-stream, the subclass @parse function may be called some final times with the
* at_eos parameter set to true, indicating that the element should not expect any more data
* to be arriving, and it should parse and remaining frames and call
* gst_video_decoder_have_frame() if possible.
* At end-of-stream, the subclass @parse function may be called some final
* times with the at_eos parameter set to true, indicating that the element
* should not expect any more data to be arriving, and it should parse and
* remaining frames and call gst_video_decoder_have_frame() if possible.
* </para></listitem>
* </itemizedlist>
* </listitem>
......@@ -125,26 +130,30 @@
* should rather be left to upstream demuxer, parser or alike. This simple
* approach caters for seeking and duration reporting using estimated input
* bitrates. To enable it, a subclass should call
* @gst_video_decoder_set_estimate_rate to enable handling of incoming byte-streams.
* @gst_video_decoder_set_estimate_rate to enable handling of incoming
* byte-streams.
*
* The base class provides some support for reverse playback, in particular
* in case incoming data is not packetized or upstream does not provide
* fragments on keyframe boundaries. However, the subclass should then be prepared
* for the parsing and frame processing stage to occur separately (in normal
* forward processing, the latter immediately follows the former),
* The subclass also needs to ensure the parsing stage properly marks keyframes,
* unless it knows the upstream elements will do so properly for incoming data.
* fragments on keyframe boundaries. However, the subclass should then be
* prepared for the parsing and frame processing stage to occur separately
* (in normal forward processing, the latter immediately follows the former),
* The subclass also needs to ensure the parsing stage properly marks
* keyframes, unless it knows the upstream elements will do so properly for
* incoming data.
*
* The bare minimum that a functional subclass needs to implement is:
* <itemizedlist>
* <listitem><para>Provide pad templates</para></listitem>
* <listitem><para>
* Inform the base class of output caps via @gst_video_decoder_set_output_state
* Inform the base class of output caps via
* @gst_video_decoder_set_output_state
* </para></listitem>
* <listitem><para>
* Parse input data, if it is not considered packetized from upstream
* Data will be provided to @parse which should invoke @gst_video_decoder_add_to_frame and
* @gst_video_decoder_have_frame to separate the data belonging to each video frame.
* Data will be provided to @parse which should invoke
* @gst_video_decoder_add_to_frame and @gst_video_decoder_have_frame to
* separate the data belonging to each video frame.
* </para></listitem>
* <listitem><para>
* Accept data in @handle_frame and provide decoded results to
......@@ -177,16 +186,17 @@
* on whether forward or reverse playback is requested.
*
* Forward playback:
* * Incoming buffer -> @parse() -> add_to_frame()/have_frame() -> handle_frame() ->
* push downstream
* * Incoming buffer -> @parse() -> add_to_frame()/have_frame() ->
* handle_frame() -> push downstream
*
* Reverse playback is more complicated, since it involves gathering incoming data regions
* as we loop backwards through the upstream data. The processing concept (using incoming
* buffers as containing one frame each to simplify things) is:
* Reverse playback is more complicated, since it involves gathering incoming
* data regions as we loop backwards through the upstream data. The processing
* concept (using incoming buffers as containing one frame each to simplify
* things) is:
*
* Upstream data we want to play:
* Buffer encoded order: 1 2 3 4 5 6 7 8 9 EOS
* Keyframe flag: K K
* Keyframe flag: K K
* Groupings: AAAAAAA BBBBBBB CCCCCCC
*
* Input:
......@@ -210,19 +220,20 @@
* this:
*
* while (gather)
* take head of queue and prepend to parse queue (this reverses the sequence,
* so parse queue is 7 -> 8 -> 9)
* take head of queue and prepend to parse queue (this reverses the
* sequence, so parse queue is 7 -> 8 -> 9)
*
* Next, we process the parse queue, which now contains all un-parsed packets (including
* any leftover ones from the previous decode section)
* Next, we process the parse queue, which now contains all un-parsed packets
* (including any leftover ones from the previous decode section)
*
* for each buffer now in the parse queue:
* Call the subclass parse function, prepending each resulting frame to
* the parse_gather queue. Buffers which precede the first one that
* produces a parsed frame are retained in the parse queue for re-processing on
* the next cycle of parsing.
* produces a parsed frame are retained in the parse queue for
* re-processing on the next cycle of parsing.
*
* The parse_gather queue now contains frame objects ready for decoding, in reverse order.
* The parse_gather queue now contains frame objects ready for decoding,
* in reverse order.
* parse_gather: 9 -> 8 -> 7
*
* while (parse_gather)
......@@ -233,8 +244,8 @@
* Processing the decode queue results in frames with attached output buffers
* stored in the 'output_queue' ready for outputting in reverse order.
*
* After we flushed the gather queue and parsed it, we add 4 to the (now empty) gather queue.
* We get the following situation:
* After we flushed the gather queue and parsed it, we add 4 to the (now empty)
* gather queue. We get the following situation:
*
* gather queue: 4
* decode queue: 7 8 9
......@@ -262,7 +273,7 @@
* output queue:
*
* gather queue: 4
* decode queue:
* decode queue:
* output queue: 9 8 7 6 5
*
* Now output all the frames in the output queue, picking a frame from the
......@@ -287,7 +298,7 @@
* Decoded output:
*
* gather queue: 1
* decode queue:
* decode queue:
* output queue: 4 3 2
*
* Leftover buffer 1 cannot be decoded and must be discarded.
......
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