decodebin

Documentation

Overview

This example demonstrates the use of the decodebin element.

The decodebin element tries to automatically detect the incoming format and to autoplug the appropriate demuxers / decoders to handle it. and decode it to raw audio, video or subtitles. Before the pipeline hasn't been prerolled, the decodebin can't possibly know what format it gets as its input. So at first, the pipeline looks like this:

{filesrc} - {decodebin}

As soon as the decodebin has detected the stream format, it will try to decode every contained stream to its raw format. The application connects a signal-handler to decodebin's pad-added signal, which tells us whenever the decodebin provided us with another contained (raw) stream from the input file.

This application supports audio and video streams. Video streams are displayed using an autovideosink, and audiostreams are played back using autoaudiosink. So for a file that contains one audio and one video stream, the pipeline looks like the following:

                       /-[audio]-{audioconvert}-{audioresample}-{autoaudiosink}
{filesrc}-{decodebin}-|
                       \-[video]-{videoconvert}-{videoscale}-{autovideosink}

Both auto-sinks at the end automatically select the best available (actual) sink. Since the selection of available actual sinks is platform specific (like using pulseaudio for audio output on linux, e.g.), we need to add the audioconvert and audioresample elements before handing the stream to the autoaudiosink, because we need to make sure, that the stream is always supported by the actual sink. Especially Windows APIs tend to be quite picky about samplerate and sample-format. The same applies to videostreams.