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123 lines
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ReStructuredText
.. Copyright (c) 2008-2023 OpenShot Studios, LLC
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(http://www.openshotstudios.com). This file is part of
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OpenShot Video Editor (http://www.openshot.org), an open-source project
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dedicated to delivering high quality video editing and animation solutions
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to the world.
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.. OpenShot Video Editor is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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.. OpenShot Video Editor is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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.. You should have received a copy of the GNU General Public License
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along with OpenShot Library. If not, see <http://www.gnu.org/licenses/>.
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.. _playback_ref:
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Playback
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========
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The preview window is where video & audio playback takes place in OpenShot Video Editor. The preview window
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utilizes real-time video rendering, caching, re-sampling, and image scaling. This is the primary area for watching
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back (and listening to) your edits, giving you the feedback needed to make adjustments. It is also one of the most
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costly operations to your CPU, and requires a modern computer and some reasonable assumptions and factors (listed below).
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Real-Time Preview
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-----------------
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Many factors affect how smoothly the **real-time video preview** can playback on your computer. This requires a fast, modern
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multi-threaded CPU, lots of RAM (memory), and a modern GPU. We have listed many of the important factors below.
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.. table::
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:widths: 22 80
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================== ============
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Factor Description
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================== ============
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CPU If your CPU is too slow or has too few cores, you will likely experience a slow, choppy preview.
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We recommend installing OpenShot on fairly modern computer. See :ref:`min_system_req_ref` for
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more details on the hardware requirements for OpenShot Video Editor.
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Memory If your available RAM memory is too limited, you will likely see huge drops in real-time
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performance, and your entire system will lag. We recommend installing additional RAM in your
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computer, if possible. See :ref:`min_system_req_ref`.
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Cache Your cache settings in the OpenShot Preferences are very important for determining how many
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frames to processes in advance. A value too low or too high can cause lag during the real-time
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video preview. The cache is also related to the available RAM. The higher the cache values, the more
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RAM and CPU is needed. We recommend experimenting with the Cache Preferences in OpenShot if you are
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experiencing issues with smooth playback. This same caching system also prepares frames ahead of time
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during export, speeding up the final render. See :ref:`preferences_cache_ref`.
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Preview Size The height x width of your preview dock (widget) is very important for smooth real-time previews.
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The larger the window size, the more pixels must be rendered per frame, and the more CPU and RAM
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are required. It is recommended to keep reducing the preview window size until you achieve smooth
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video playback. On a slower computer, the preview window size might need to be very small for
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real-time previews (i.e. 320 x 240).
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Profile Your project profile determines which size (width x height) and frame rate (FPS) are used during both
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playback and exporting. For example, if you are using a FHD 1920x1080 sized profile, you can also choose a
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smaller profile with the same aspect ratio (``16x9`` in this example), to improve the preview speed
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on slower computers. See :ref:`profiles_ref` for more information on available profiles.
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FPS (Frame Rate) The FPS of your project is also very important, and a large factor for smooth video playback. For
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example, a 60 FPS video must render twice the number of frames, compared to a 30 FPS video. If
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you are experiencing slow downs in real-time performance, it can be helpful to reduce your project's
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FPS to a lower value, such as 30 or 24.
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Matching Rates It is very important to match your source assets FPS and Sample Rate with your Project FPS and Project
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sample rate. If either rate does not match exactly, it requires lots of additional CPU and RAM for
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OpenShot to normalize the mismatching rates. This can lead to audio pops, mis-alignments, duplicate frames, and extra
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lag in the real-time video preview. You can right-click a file and choose :guilabel:`File Properties`, to
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inspect the source asset rates, and ensure they match your Project settings (shown at the top of OpenShot).
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See :ref:`file_properties_ref`.
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Source Assets For example, if you are editing 4K 60 FPS source assets, this is likely going to put a strain on your system. A
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common solution is using another tool (such as FFmpeg) to create a copy (or proxy) of all your source assets,
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at a lower resolution (and maybe even a lower FPS). It is recommended to keep these proxy video files
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in their own folder, separate from the original video files. Once you have completed your video editing with
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the proxy files, simply copy/paste your `*.osp` project file back into the original folder, and export
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the higher quality, original files.
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Audio Device If you are still having issues with audio lag or sync, please verify you are using the correct
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:guilabel:`Playback Audio Device` for playback (in the OpenShot Preferences). See :ref:`preferences_preview_ref`. Verify
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your default audio device (on your operating system) is using the same sample rate and all *Audio Enhancements* are disabled. On
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certain operating systems (such as Windows), mismatching sample rates or audio enhancements can cause severe audio
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/ video sync problems. Lastly, try adjusting the :guilabel:`Playback Audio Buffer Size` (lower values
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will playback audio with less delay, higher values will playback audio with a larger delay). OpenShot
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defaults to a buffer size of 512, which is reasonable for most systems, however on some systems you
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might need to lower (or raise) this value for smooth and lag-free audio playback. Be sure to restart
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OpenShot after changing the audio playback settings.
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================== ============
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Audio Troubleshooting
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---------------------
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If you are still experiencing audio related issues, and the above real-time playback factors did not resolve
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your issue, here are some additional troubleshooting steps you can take.
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.. table::
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:widths: 22 80
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================== ============
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Step Description
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================== ============
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Latest Daily Build Verify you are running the latest daily build of OpenShot: https://www.openshot.org/download#daily
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Clean Install See :ref:`preferences_reset_ref` for a clean install
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Audio Device Check that the Playback Audio Device is set correctly for your sound output under Preferences
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in the Preview tab. Restart OpenShot after changing the settings. You can also try a different
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audio device (USB, audio over HDMI from the video card, headphones, etc.) to rule out other audio issues.
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Disable `automatic sound suppression` for voice calls during microphone activity, and disable
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`Audio Enhancements` under the advanced settings tab of your audio device (not all audio devices
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have these settings). See :ref:`preferences_preview_ref`.
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Audio Buffer Size The audio buffer size is the amount of audio samples which must first be buffered in OpenShot before
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audio playback can begin. If this value is too low, you might experience audio break-up / crackle / popping.
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If this value is too high, you might experience delays or lag before audio playback begins. OpenShot
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defaults this value to 512, which is a reasonable default for most systems, which should provide smooth
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audio playback with minimal noticeable lag or delay. However, on some systems this value might need
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to be adjusted up or down, for in-sync and lag-free audio playback. The range is 128 to 4096.
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Sample Rate Ensure that the `Default Audio Sample Rate` and `Default Audio Channels` on the Preview tab of the
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Preferences window match your hardware. You can also check these settings in the operating system
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control panel (i.e. Windows Sound Control Panel). See :ref:`preferences_preview_ref`.
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Volume Ensure that the volume does not exceed 100% on overlapping clips (such as an audio track combined
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with a video track). Lower the volume on individual clips if needed. See :ref:`clip_volume_mixing_ref`.
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Headphones If you're using headphones, plug them in before starting OpenShot. Launching OpenShot with no
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speakers, headphones, or valid audio playback device can cause OpenShot to freeze during playback.
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OS Updates Update your operating system and any pending security updates. Some audio issues, especially
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audio device specific issues, can be resolved with an operating system update.
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================== ============
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