Hi,
I've experimented A/V sync issues when I transcode HDV .m2t (1440x1080) created with my Canon HV10 to DNxHD. Whenever I try to transcode a .m2t clip to DNxHD (I use 185 Mb/50i profile) I get audio out of sync with video. Anyone experimented the same issues? Should I have to try 120 Mb/50i? A ffmpeg command? Any suggestions?
Thank you,
Ignazio

Could you maybe upload a sample (source and transcoded)?

Hi, thank you for your reply and interest. I have the feeling that the more the clip is long, the longer is the delay between audio and video so I think I should upload a very big clip (especially the DNxHD one!!!!). I'll shoot an example clip of me speaking and I will try to upload them at the beginning of next week from work. I cannot do it at home because I have limited acces to the internet. Can you suggest me some free file hosting websites?
I forgot to mention that I've experimented another issue in the transcoded files, at least when dragged to the kdenlive timeline: there are often (if not always) some black frames at the end of each clip...
Thanks a lot again,
Ignazio

You can upload it to my webspace. Please don't upload more than 8 GB :)
I'll send you the login.

Thank you so much, I appreciate.

transcode just calls ffmpeg with the options configured in the Kdenlive transcode profile, but why are you convering HDV to DNxHD? HDV should work fine directly.

You're right, but If I edit HDV without transcoding I see RAM usage increasing. I guess It has to do with "long GOP thing" real time editing. If I edit HDV directly I get bad rendered transitions, maybe my PC is not powerful enough (AMD Athlon XP 64x2 6000+ with 2GB ram and 500GB 7200rpm). Furthermore, correct me if I'm wrong, I can work easier on single frames and I should mantain a good video quality during all the edit process, not to mention colour correction... Why don't try to use this great (they say) open source codec if it should bring advantages? The problem is that I exprienced drawbacks too... I didn't have much time this week but I'll try to do some more tests, not only transcoding, but also shooting and capturing... I did a quick test last week capturing a short clip (realtime via firewire with dvgrab and no tape) with me speaking and the .mt2 file had A/V sync issues itself...
Thanks Dan and greetings from me and a hot (like hell) italian summer.

(You're aware of the fact that DNxHD is lossy? Just a hint. FFV1 is not.)

I'm aware of the quality loss (which I can't see) of DNxHD. But it should be a small quality loss and only at the beginning of my workflow, right? Because "upsampling" should help to keep quality during all the editing process (this is what I read on the net). Do you suggest me to use FFV1? Is it included in the "batch transcode" function in Kdenlive (I'm at work under Win now)? Is the bitrate very high (difficult to handle)?
For my last two "works" I exported audio, re-imported in Kdenlive, dragged in the timeline and "hand-synced" with video clip by clip, but it's a pain in the neck...
I like Kdenlive, it's enough for my need (sure MORE than enough) and I want to continue to use it!
Ignazio

render with time codes in it. the code isn't that much of the screen. Its the only way I can get it to work.

@lordofthestrings, you do not get the A/V sync issues when using HDV directly, only when transcoding to DNxHD? Is this correct?
Yes, FFV1 has a higher bitrate and is not so fast for decoding. But from what I read it is quite cool (very low bitrate for a lossless codec eg). I've recently used it because recordmydesktop recorded .ogv you can't work with.
The option to convert to ffv1 isn't in the transcode menu, but you can use
$ ffmpeg -i file.m2t -f avi -vcodec ffv1 -acodec flac -ar 48000 -ab 1024k outfile.avi
on the command line to give it a try.

Correct. Only when trascoding to DNxHD. Thank you very much for the command, I'll give it a try tonight and I hope my cpu will handle it!

Thank you. Please, can you explain me better? I heard about timecodes many times but I don't know how to use them... How do I get time codes in my video clips? (dvgrab options?) Ho do I see them in Kdenlive? I guess I need them to easily correct A/V sync in post...

Allright. Even though I couldn't upload anything I'll tell you about some tests I did, wich brought just more confusion into my mind.
I transcoded a .m2t file to FFV1 with the command you suggest me but the file is unplayable in Kdenlive. The file had almost the same bitrate the DNxHD profile I used had, about 183 Mbps. Are you sure there is no loss? Is the bitrate in your command fixed? If yes, at what value?
Then I recorded a small clip of me saying "this is a test, a test" and the .m2t file sounded perfectly synced. Then I transcoded it to DNxHD 185 Mb/s 50i and played the file with smplayer with VDPAU. Result: audio out of sync. So I dragged the same file in Kdenlive and pressed play. A/V sync was OK. VLC couldn't play the audio stream...
I dragged another (longer) DNxHD clip in Kdenlive. This was recoded three weeks ago. Audio was out of sync.
I think that the sync issues may have to do with the lenght of the footage...
If I edit HDV directly I have very often freezing clips (in the beginning) after cuts/transitions, during the editing process and also in the rendered file :-(
One question: If I render back in HDV do you think 2 pass render make some difference in quality?

When trying out the FFV1 transcode I notice it contrast expands my DSLR source material, so where I had blacks at around 12 they are now crushed to 0 and whites that were no higher than 250 stretched up to 255 and clipping a fair amount. Wouldn't call it lossless. :-) But interesting to try out different codecs.

**EDIT** Strike that, it may be expanding. :-)More tests.