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|ID||Project||Category||View Status||Date Submitted||Last Update|
|0001034||Kdenlive||Rendering||public||2009-07-10 05:41||2010-09-22 17:53|
|Product Version||Recent git|
|Target Version||0.7.6||Fixed in Version||0.7.6|
|Summary||0001034: A/V drifts out of sync in long HD 1080p 23.98Hz projects|
|Description||I've been experiencing a problem where the audio and video drift out of sync in the rendered file where the frame rate is 23.98 Hz. Here's a way to reproduce it:|
(1) Create a new project with the HD 1080p 23.98Hz profile.
(2) Setup the timeline like this:
00:00:00:00 - 00:01:00:00 Video Track: Color clip (black)
00:01:00:00 - 00:01:01:00 Video Track: Color clip (white), Audio Track: 1 sec tone
00:01:01:00 - 01:00:00:00 Video Track: Color clip (black)
01:00:00:00 - 01:00:01:00 Video Track: Color clip (white), Audio Track: 1 sec tone
01:00:01:00 - 01:01:00:00 Video Track: Color clip (black)
This has the effect of creating a movie that's about 1 hour long. One minute into the video, the screen turns white for 1 second and at the same time a tone plays. The same white screen/tone combination plays one hour into the movie.
Here's the file I used for a tone: http://www.mikeadkins.net/kdenlive/Tone.wav [^]
(3) Render the project using MPEG-2.
(4) Play the rendered file in an external player. The tone and white screen are well synchronized at the 1 minute mark, but the tone precedes the white screen by almost two seconds at the 1 hour mark.
Alternatively, you could import the rendered file into a new kdenlive project. Exploring the file with the project monitor show that the white screens appear on exactly the correct frames, but the audio thumbnail clearly shows the audio is too early at the 1 hour mark.
My math tells me that the audio is being rendered at a speed about 0.05% too fast for some reason.
If I perform the same experiment using the HD 1080p 24Hz profile the sync is perfect throughout the file.
|Tags||No tags attached.|
|Build/Install Method||Manual build from SVN|
I now think this is an MLT bug. The function mlt_sample_calculator seems to be trying to compute the number of audio samples in a frame. With this strange frame rate, there is a combination of finite precision floating point arithmetic and integer truncation that causes this calculation to be off by one sample per frame. This error accumulates when rendering a long duration project and causes a noticeable A/V sync issue.
I've posted more details and a proposed patch that seems to work for me on the mlt-devel mailing list.
We'll see what happens!
|Your more comprehensive patch was applied to MLT git commit 33098e.|
|2009-07-10 05:41||madkins||New Issue|
|2009-07-10 05:41||madkins||Build/Install Method||=> Manual build from SVN|
|2009-07-19 23:38||j-b-m||Relationship added||related to 0001033|
|2009-07-26 18:17||madkins||Note Added: 0003733|
|2009-08-08 05:08||ddennedy||Note Added: 0003777|
|2009-08-08 05:08||ddennedy||Status||new => resolved|
|2009-08-08 05:08||ddennedy||Fixed in Version||=> Recent git|
|2009-08-08 05:08||ddennedy||Resolution||open => fixed|
|2009-08-08 05:08||ddennedy||Assigned To||=> ddennedy|
|2009-09-10 01:46||xzhayon||Target Version||=> future version|
|2009-10-08 20:20||j-b-m||Fixed in Version||Recent git => 0.7.6|
|2010-02-02 10:35||j-b-m||Fixed in Version||0.7.6 => 0.7.7|
|2010-02-02 10:37||j-b-m||Fixed in Version||0.7.7 => 0.7.6|
|2010-02-02 10:38||j-b-m||Status||resolved => closed|
|2010-09-22 17:53||Granjow||Target Version||future version => 0.7.6|
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