aac in ardour


(Innits) #1

Hey there,
I’ve been importing a mp4 video file from my phone(using filmic pro). I extract the audio from the video and when it imports to the timeline the audio region is always few frames shorter in the end then the video file. The audio is recorded in aac format. I don’t see much syncinc problem because the video is short but I was wondering if I have a long video file then it must start to get well out of sync. is there any problems with Ardour and aac format or could it be the mp4 video format? it seems like the video is converted to .avi
thanks
Stinni


(Robin Gareus) #2

What framerate was the video filmed at?
If you didn’t use one of the SMPTE standard rates, you may need Session > Properties > Sync > Use Video File’s FPS (instead of session timecode).

PS. the .avi is used as internal proxy only (fast seeking, low CPU overhead, small video-timeline)
PPS. Generally there are no known issues even with long videos, but it may well be some specific issue with the given codec or phone. Ardour’s video-timeline was aimed for pro-postproduction.


(Innits) #3

Hey there @x42,
thanks for the response. Yes it asks you to make your session the same FPS as the video when you import it and I double checked and its the same frame rate so that shouldn’t be the problem. This doesn’t seem to be a problem when I import a .mov file (h.264 and PCM) from the canon 5d markii. Maybe it’ll work better if I first import my phone .mp4 file into premier pro and export it with some other file extensions.
I’m also seeing couple of frames blank in the video in ardour. It must be something with the phone or codec. I see glitches also when I import into adobe after effects but not in premier pro, then all is fine.
weird !


(Mikael Hartzell) #4

It’s not unheard of audio being a little bit different length than the video. Audio can even start before or after the video starts. There is a timestamp on both and that way the video player keeps them in sync while playing. Timestamps can get lost during a conversion. I’m not speaking about Ardours video features here, but in general about video files. I think it’s quite common that audio and video on dvds and bluerays aren’t exatly the same length and they don’t need to be because the player just keeps playing video and audio frames according to their time stamps.


(Innits) #5

@mhartzel : thats an interesting thing. I didn’t know that the timestamp could get lost in the conversion. Perhaps thats it because it seems to me that the video and sound (did a test by snapping my fingers) are in sync by listening and watching but not on the timeline. this could be a problem when adding sounds to the movie and trying to visually sync it to the videos original audio file on the timeline. Maybe I’m just blowing up something that wont be a problem. like I say, I’ll try to export the .mp4 file from premier pro tonight and see if it works better in Ardour after that. :


(Chris) #6

if I have a long video file then it must start to get well out of sync

Have you tried a long recording yet? Perhaps there is always just one frame dropped off the end, or something similar that doesn’t scale with the length of the original recording.

also seeing couple of frames blank in the video in ardour

Check whether that is still the case when you zoom in to that section of the timeline. Sometimes the thumbnails don’t look quite right when zoomed out, but as you zoom into that part of the timeline and the video thumbnails are redrawn they look fine.

is there any problems with Ardour and aac format

When importing videos Ardour uses ffmpeg to convert, you could try some experiments just using the standard ffmpeg tools to convert formats, split video and audio to see if the audio is just a little shorter than video for some reason.