Hello.

Recently I recorded some event, and because I knew the sound was going to be bad from the camera mic, I also recorded separately the sound using a MP3 player. Now I'm trying to sync video and audio, and something strange occurs. I sync them at the start of the video, and when I play it, it starts to drift away. At 1 minute on the video the difference can be heard, and it goes bad from here on. The video lags behind the audio. I've tried to reencode the original video with ffmpeg and with kdenlive without luck.
I'm using Slackware 14, Kdenlive 0.9.6, MLT 0.8.8 and ffmpeg 1.1.2. The packages where downloaded from slacky.eu, and I used the dependencies that slacky told me I needed. In fact, the configuration assistant ends with a 100% correct.

Thanks.

It's probably worthwhile lining the tracks up in Audacity or another audio program as well, just to check the problem is not with Kdenlive.
I imagine the drift is due to recording at different sample rates - say, 48Hz on the camera and 44.1Hz on the MP3 recorder.

You can try opening the 44.1Hz file in audacity, changing the project to 48Hz, and exporting to FLAC or WAV file. Then import this new file and it should line up.
if not, as a last resort you can apply a 'speed' effect to the audio with a value of 99.5 or 100.5 or something very subtle. There's probably a mathematical way to work it out, but trial and error also works! I would recommend working in Audacity rather than Kdenlive for this.

To avoid this problem in the future make sure you always record in the same sample rate on each device, and make sure you record audio on camera as well as externally - even if it's not usable for the edit it helps for checking sync.

sammuirhead wrote:It's probably worthwhile lining the tracks up in Audacity or another audio program as well, just to check the problem is not with Kdenlive.
I imagine the drift is due to recording at different sample rates - say, 48Hz on the camera and 44.1Hz on the MP3 recorder.

THAT.
The audio tracks lose sync in audacity, but I've tried to convert the MP3 recorder one to the video sample rate and didn't worked, so I'll keep trying. At least now I have a good starting point. BTW the MP3 recorder is 24000 mono and the video is 48000 stereo.

To avoid this problem in the future make sure you always record in the same sample rate on each device, and make sure you record audio on camera as well as externally - even if it's not usable for the edit it helps for checking sync.

The devices I used weren't even mine, and I think the MP3 didn't even had a configuration option for voice recordings. I have the audio from the camera, so I'll work with it in trying to solve the sync problem.

I'll try to tweak the audio duration in audacity until they sync, and then use that audio in kdenlive. Thanks a lot for the help.