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137 lines
4.2 KiB
Markdown
137 lines
4.2 KiB
Markdown
# Basics (GStreamer command-line cheat sheet)
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## Playing content
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These examples assume that bash variable `SRC` to be set to a video file (e.g. an mp4 file). You can do this by, e.g.
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```
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export SRC=/home/me/videos/test.mp4
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```
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### Play a video (with audio)
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The magical element `playbin` can play anything:
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```
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gst-launch-1.0 playbin uri=file://$SRC
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```
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This works with video, audio, RTMP streams, and so much more.
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The 'bin' in 'playbin' means that under-the-hood, it's a collection of elements. We could split it down into the individual components:
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```
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gst-launch-1.0 filesrc location=$SRC ! \
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qtdemux name=demux demux.audio_0 ! queue ! decodebin ! audioconvert ! audioresample ! \
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autoaudiosink \
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demux.video_0 ! queue ! \
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decodebin ! videoconvert ! videoscale ! autovideosink
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```
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### Play a video (no audio)
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```
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gst-launch-1.0 -v uridecodebin uri="file://$SRC" ! autovideosink
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```
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which could also have been done as:
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```
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gst-launch-1.0 -v filesrc location="$SRC" ! decodebin ! autovideosink
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```
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### Play just the audio from a video
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```
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gst-launch-1.0 -v uridecodebin uri="file://$SRC" ! autoaudiosink
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```
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### Visualise the audio:
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```
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gst-launch-1.0 filesrc location=$SRC ! qtdemux name=demux demux.audio_0 ! queue ! decodebin ! audioconvert ! wavescope ! autovideosink
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```
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(or replace `‘wavescope` with `spectrascope` or `synaescope` or `spacescope`)
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Or even better visualisation:
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```
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gst-launch-1.0 filesrc location=$SRC ! decodebin ! tee name=t ! queue ! audioconvert ! wavescope style=color-lines shade-amount=0x00080402 ! alpha alpha=0.5 ! videomixer name=m background=black ! videoconvert ! vertigotv ! autovideosink t. ! queue ! audioconvert ! spacescope style=color-lines shade-amount=0x00080402 ! alpha alpha=0.5 ! m. t. ! queue ! autoaudiosink
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```
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### Add filters
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Here's the 'vertigo' filter:
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```
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gst-launch-1.0 -v filesrc location="$SRC" ! decodebin ! videoconvert ! vertigotv ! autovideosink
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```
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Try also ‘rippletv’, ‘streaktv’, ‘radioactv’, ‘optv’, ‘quarktv’, ‘revtv’, ‘shagadelictv’, ‘warptv’ (I like), ‘dicetv’, ‘agingtv’ (great), ‘edgetv’ (could be great on real stuff)
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### Add a clock
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```
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gst-launch-1.0 -v filesrc location="$SRC" ! decodebin ! clockoverlay font-desc="Sans, 48" ! videoconvert ! autovideosink
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```
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### Resize video
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```
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gst-launch-1.0 -v filesrc location="$SRC" ! decodebin ! videoconvert ! videoscale ! video/x-raw,width=100 ! autovideosink
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```
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### Change framerate
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Changing framerate is quiet common, as the world does not have a consistent standard. Facebook Live wants 30fps, for example.
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Change framerate:
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```
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gst-launch-1.0 -v filesrc location="$SRC" ! decodebin ! videoconvert ! videorate ! video/x-raw,framerate=5/1 ! autovideosink
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```
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And of course you can resize the video and change the framerate:
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```
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gst-launch-1.0 -v \
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filesrc location="$SRC” ! \
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decodebin ! videoconvert ! videoscale ! video/x-raw,width=100 ! videorate ! video/x-raw,framerate=5/1 ! \
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autovideosink
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```
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Here's a more complete example, that keeps the audio, and changes the size and framerate:
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```
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gst-launch-1.0 filesrc location=$SRC ! \
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qtdemux name=demux demux.audio_0 ! queue ! decodebin ! audioconvert ! audioresample ! \
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autoaudiosink \
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demux.video_0 ! queue ! \
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decodebin ! videoconvert ! videoscale ! videorate ! \
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'video/x-raw, format=(string)I420, width=(int)320, height=(int)240, framerate=(fraction)30/1' ! \
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autovideosink
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```
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### Play an MP3 audio file
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Set the environment variable `$AUDIO_SRC` to be the location of the MP3 file. Then:
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```
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# All three of these do the same thing:
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gst-launch-1.0 playbin uri=file://$AUDIO_SRC
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gst-launch-1.0 -v uridecodebin uri="file://$AUDIO_SRC" ! autoaudiosink
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gst-launch-1.0 -v filesrc location=$AUDIO_SRC ! mpegaudioparse ! decodebin ! autoaudiosink
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```
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### Play files back to back
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See (https://coaxion.net/blog/2014/08/concatenate-multiple-streams-gaplessly-with-gstreamer/)[https://coaxion.net/blog/2014/08/concatenate-multiple-streams-gaplessly-with-gstreamer/]
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### Jumping to a certain point in a video/audio (seek/rewind/restart)
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As far as I know, this isn't possible on the command-line. But it is possible as code. Here is a simple Python example:
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[/python_examples/seeking.py](/python_examples/seeking.py)
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