Bug 464558

Summary:	When speeding up playback, audio is severely distorted
Product:	[Applications] kdenlive	Reporter:	Adam Jones <domdomegg+kde>
Component:	Monitors & Playback	Assignee:	Jean-Baptiste Mardelle <jb>
Status:	REPORTED ---
Severity:	normal	CC:	fritzibaby, ruro.report
Priority:	NOR
Version First Reported In:	22.04.3
Target Milestone:	---
Platform:	Ubuntu
OS:	Linux
URL:	https://youtu.be/09h__B7XhpU
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Adam Jones 2023-01-20 15:53:12 UTC

SUMMARY
When speeding up playback (for example with the >> icon underneath the Project Monitor, or hitting the 'L' key), audio is severely distorted. It seems to have a static noise and tiny skips.

STEPS TO REPRODUCE
1. Start playing a video in the timeline
2. Increase the speed to 2x using the 'L' key
3. Listen to the audio

OBSERVED RESULT
Audio plays back with static and skips. It seems particularly bad with voices speaking.

EXPECTED RESULT
Audio plays back correctly.

IMPACT
This makes editing long videos more difficult, because it's hard to watch them back quickly to either find the most important parts or identify parts that need editing.

SOFTWARE/OS VERSIONS
Kdenlive: Kdenlive Version 22.04.3, using MLT version 7.8.0
OS: Ubuntu 20.04.5 LTS

ADDITIONAL INFORMATION
- This has been noticed by others since 2018, but I couldn't find a formal bug report: https://forum.kde.org/viewtopic.php?f=279&t=151473
- This has also been recorded in other bugs, e.g. https://bugs.kde.org/show_bug.cgi?id=455563 (which you can hear the static in when it is at 2x speed)
- It's clear Kdenlive can play back videos at a faster rate without this static effect: using the 'Change Speed' dialogue with Pitch Compression gives the desired result.
- Demonstration here: https://youtu.be/09h__B7XhpU