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IDProjectCategoryView StatusDate SubmittedLast Update
0001738KdenliveRenderingpublic2010-08-10 02:402010-08-27 12:15
Assigned To 
PlatformIntel 64bit (Core i7)OSLinuxOS Version2.6.34
Product VersionRecent git 
Target VersionFixed in Version 
Summary0001738: Rendering produces audio artifacts
DescriptionWhe I render my projects, the generated audio is wrong, with some artifacts.
Steps To Reproduce1) Load the attached sound-issue.mp4 file and put in the project
2) Click Render
3) select H264 and for example 6000kpbs 1pass

4) the result file will contain some audio artifacts (4 to 5 seconds and in the last second of the video: 7s)
TagsNo tags attached.
Build/Install MethodManual build from SVN
Attached Files? file icon sound-issue.mp4 [^] (2,579,605 bytes) 2010-08-10 02:40
? file icon sound-result-final-render-artifacts.mp4 [^] (6,485,640 bytes) 2010-08-10 02:43
? file icon sample.mp4 [^] (1,441,451 bytes) 2010-08-10 20:10
? file icon kdenlive-artifacts.mp4 [^] (3,809,131 bytes) 2010-08-10 20:11
? file icon artifacts.kdenlive [^] (6,141 bytes) 2010-08-10 20:11

- Relationships

-  Notes
dfraga (reporter)
2010-08-10 02:41

I use the 720p 30fps profile.
dfraga (reporter)
2010-08-10 02:44

The sound-result-final-artifacts.mp4 is the generated rendered file with sound artifacts.
tidris769 (reporter)
2010-08-10 05:56

I listened to both files several times and they sound identical to me.
LeHomard (developer)
2010-08-10 11:27

I thought I heard some sort of a sound artifact, but after listening several times it might actually be my imagination.

Can you hear any sound distortion when rendering in a lossless format ? Have you tried exporting audio only ?
dfraga (reporter)
2010-08-10 16:49

tidris769 in the sound-result-final-render-artifacts.mp4 you can hear a small artifact in the end (7s) on the right channel. It's very subtle. And between 4 and 5s. Maybe I] should record some other kind of sound?

LeHomard I rendered in RAW DV format and there's no artifacts, perfect audio. Could if be H264's fault?

I also exported to mpeg2 and the audio is fine. It only happens with H264. Thanks.
tidris769 (reporter)
2010-08-10 17:11
edited on: 2010-08-10 17:17

Maybe this is something that depends on the kind of speakers used and/or the version of the audio codec used for playback. I listen through the speakers on my LCD monitor, and use a very recent version of ffmpeg (which contains the audio codec). Also my ears have 50 years of listening experience and I don't speak Portuguese.

dfraga (reporter)
2010-08-10 20:12

Ok tidris769. I use the Edifier E3100 speakers which are very good and has a high fidelity. I recorded something more obvious... I sent the following:

sample.mp4 -> original file
kdenlive-artifacts.mp4 -> output with audio artifacts
artifacts.kdenlive -> project file using sample.mp4 (you can try there)

I said 5 "a". You can notice artifacts on the first 4 "a", mainly in the fourth one (right channel). Listen to it closely and you will notice it. It's like the audio is distorted or saturated.

I hope it helps you to debug it. Thanks!

Ps: the profile I use is the same as 720p 30 fps but with "threads=4" option. Using the original 720p 30fps profile gives me the same artifacts.
tidris769 (reporter)
2010-08-10 21:38
edited on: 2010-08-10 23:04

I still can't hear a difference through the small speakers in my LCD monitor, but that doesn't mean there isn't one.

You are using a rendering profile with the lossy audio codec AAC. That means the output audio will always be lower quality than the input audio. The degradation depends on the audio bit rate specified by the profile. Higher bit rate means less degradation. If your speakers and amplifier are good enough you might very well be able to hear the difference.

If you want higher fidelity audio you can try increasing the audio codec bit rate, or use a lossless audio codec. However be aware that when you upload the video to YouTube it will be transcoded by them and you will have no control over the audio codec and bit rate they use, so your audio will end up being degraded anyways.

LeHomard (developer)
2010-08-10 22:57

The h264 profiles use libfaac for audio encoding, and even at 6000k the audio is only 128k. So the audio won't be super quality anyway, and there might be issues with the AAC encoding (or decoding...).

Try using mp3 or vorbis.
dfraga (reporter)
2010-08-12 07:31

Ok thank you both. I'll stick with mp3.
ddennedy (developer)
2010-08-15 08:02

In a brief review of the comments here, it does seems like a AAC encoding problem. Even if the render profile says "libfaac" sometimes it might use the much less mature native AAC encoder of FFmpeg depending upon versions and build configurations (see list of codecs in Kdenlive Settings > Run Config Wizard.

Did anyone conclude that mp3 does not reproduce the problem?

- Issue History
Date Modified Username Field Change
2010-08-10 02:40 dfraga New Issue
2010-08-10 02:40 dfraga File Added: sound-issue.mp4
2010-08-10 02:41 dfraga Note Added: 0005502
2010-08-10 02:43 dfraga File Added: sound-result-final-render-artifacts.mp4
2010-08-10 02:44 dfraga Note Added: 0005503
2010-08-10 05:56 tidris769 Note Added: 0005504
2010-08-10 11:27 LeHomard Note Added: 0005505
2010-08-10 11:27 LeHomard Assigned To => LeHomard
2010-08-10 11:27 LeHomard Status new => feedback
2010-08-10 16:49 dfraga Note Added: 0005506
2010-08-10 16:49 dfraga Status feedback => assigned
2010-08-10 17:11 tidris769 Note Added: 0005507
2010-08-10 17:17 tidris769 Note Edited: 0005507 View Revisions
2010-08-10 20:10 dfraga File Added: sample.mp4
2010-08-10 20:11 dfraga File Added: kdenlive-artifacts.mp4
2010-08-10 20:11 dfraga File Added: artifacts.kdenlive
2010-08-10 20:12 dfraga Note Added: 0005509
2010-08-10 21:38 tidris769 Note Added: 0005510
2010-08-10 21:41 tidris769 Note Edited: 0005510 View Revisions
2010-08-10 22:57 LeHomard Note Added: 0005511
2010-08-10 22:58 LeHomard Status assigned => feedback
2010-08-10 23:04 tidris769 Note Edited: 0005510 View Revisions
2010-08-12 07:31 dfraga Note Added: 0005576
2010-08-12 07:31 dfraga Status feedback => assigned
2010-08-15 08:02 ddennedy Note Added: 0005629
2010-08-27 12:15 LeHomard Assigned To LeHomard =>
2010-08-27 12:15 LeHomard Status assigned => feedback

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