[FFmpeg-devel] Ffmpeg mailing list-dev.

[Braith]

braithsproducts at gmail.com

Hello

I tried emailing a query to ffmpeg-user-owner at ffmpeg.org  last week, to see
if I ought to enquire via a mailing list or to contact a hire-developers
developer, but as I have not heard back I will try to enquire directly via
a mailing list, I have read the FAQs and think this is the right thing to
do, but please advise me if not. If I have not heard back in another week,
by 20250604 say, I will try a developer's address. Thank you.

I have been fiddling and experimenting for a few weeks and hope you do not
mind my getting in touch. I have tried to work it out myself (and with a
friend).

I would say I am an amatuer video technician, self-taught though, and with
friends who were TV engineers.
I also see the option for hire developers and would consider that too,
though I do not have a clue how much that may cost.

I use Ffmpeg, through being built into OBS, to capture and compress VHS &
similar tapes to MP4 h.264, aiming for a much more efficient manner than
many other people and businesses. This is a hobby-business sized thing, at
the moment. The difficulty doing this may be why other people capture then
process!! I may end up joining them, but I hope my idea is possible.

I believe I can use Ffmpeg to capture as a .cmd programme, which I am happy
to learn to do if req'd.

The problem I have been having, and have only fairly-recently started
trying to capture and process in real time, is that the audio seems to be
drifting, three frames at 50p during capture, cycling near and far from
correct timing every five minutes or so, and the basic sync changes upon
opening and closing of OBS by another two or three frames, backwards and
forwards, but not an exact pattern, between closes and opens of OBS.

OBS is the only software I have found like it, and is ideal, except it is
free, which is nice but also a bit difficult, as it does not have much
support. I am yet to find another piece of software that can do what it
does. Adobe Premier, Blackmagic Design Media Express, etc., do not do this.
I am so close as it is, but OBS say the sync cannot be fixed at their end.
See below.

If I was to contact the developers, my ideal would be:
To capture from a BlackMagic Design Intensity Shuttle, via 720x576 50p
progressive component input;
apply Ffmpeg filters, which I cannot quite do in OBS (option boxes that
look like I can type into them, but nothing happens if I do), chromashift
and atadenoise;
encode with single-pass CRF, I am not sure if two-pass is applicable to
CRF, but if it is, even more ideal, would be to encode with CRF in semi-two
pass like live broadcasts do, with say an eight-frame buffer (I think)
(currently tests with OBS CRF18 & veryfast give the best output I can get
in real-time if that information is of any use);
and preface the capture with a one-second test pattern image and
several-second label (as-typed of what is on the tape label).
Ideally some sort of GUI would be nice, but I am quite happy with typing to
enter fields that pop up in CMD windows (or what their proper name is), as
I have done that with a batch file my friend made for me to add chromashift
later. I do have a time base corrector that can do that, but my setup works
better without it connected, and I have four setups in parallel, and only
one TBC.

I have been told that capture then encode theoretically ought to always be
better, but the process I am designing is aimed at domestic-family tapes of
customers, and not museums, etc., though if it was good enough, I would be
very keen to get into that sort of work too using the same process, and not
having a separate capture then encode setup for those orders.

I have a friend who may be able to work out how to do this if it is
possible, without needing to hire developers, but I would like to know if
the audio drift is an OBS issue or an Ffmpeg issue, if anyone knows, and IF
what I have said above is possible, if you can tell me without having to
work it out yourself, before I ask my friend to work it out for me if he
can?

I am happy to pay developers, depending on how much, for development, or I
can make a donation for someone's time if my question is not complicated
enough to need a developer but too complicated for free advice or for my
friend to work out for me, or if I cannot afford to get development done
and have to compromise with a donation-amount solution with a limited setup
of the desired functions listed above.


Email signature deleted as per mailing list guide preferences. Not sure
about character per line limits in gmail, 78 I think google tells me, I
hope that is alright.

I like the mailing list arrangements/concepts, I have not been part of/in
one before. It sounds very interesting.

Thank you very much,
Braith



Here is what I asked OBS in a forum, and some answers, if they are of any
interest.




https://discord.com/channels/348973006581923840/768389015484760106/1374608722839601225?fingerprint=1257144696208228423&attemptId=b2da9ab6-717b-4126-a12b-d08feb9def77
Hello

If there is an email address I would be happy to enquire there.

I am having audio sync & drift issues. The sync does not stay the same
between recording starts, and between closing and opening of OBS. I am a
video technician. The audio drifts in MP4 recordings by a few frames at
50p. Setting "enable buffering" under the capture device reduces the
drifting by about half from six frames to three altogether (one ahead, two
behind, not three either way), but does not completely remove it.
Separating the audio from the video device and using it as a separate audio
input capture device does not work, as it delays the audio so it is behind
the video, this cannot be fixed by a negative audio offset. If anyone may
be able to assist or direct me elsewhere that would be appreciated. I have
been testing it with a universal counting leader (like at the start of a
film) for accurate testing. Originally I thought audio sync offset would be
all I needed, but upon testing I discovered it is wandering/drifting/moving
during a recording, not just out by a fixed amount. I have also tried
several OBS versions, including the latest (a week ago or thereabouts).

I am using CRF encoding, but I tried CBR also, and have had the same
issues. I have not tried anything other than MP4 h.264 though.

I have tried this on several computers. The one with the (we think) best
processor seemed to drift one frame less than another computer, whether
this is relevant, I do not know.

If there is a commercial help facility, for business use, please let me
know, but I seem unable to find it.

Here is a log from one computer, but not the one I did most of the testing
on, and only of course showing one set of parameters/settings in this log.

   -
   - Thank you very much,

Braith








Chiyo* — *14:44
@Braith By 50p, do you mean 50 FPS? There shouldn't be any A/V drift at any
frame rate with any container, but due to quirks of how audio encoders and
decoders work, yes, there may be some inconsistency in A/V sync between
multiple recordings. No real fix for this, but I imagine PCM would be the
least affected.
Braith* — *15:22
Hello Chiyo
50p as in progressive, yes, 50FPS, sorry.
Very odd about the drift then, as there definitely is drift.
Interesting about PCM, I will see if that is an option with my device, but
I have not seen it.
@Chiyo
I see the @Braith so think perhaps I need to use that to reply to @Chiyo Thank
you for your help.
There was up to six frames of drift at one point.
Chiyo* — *15:31
!vlc @Braith Most people are able to record for several hours at a time
without any noticeable desync or drift. Are you recording something that
requires perfect A/V sync? If yes, you might need something other than
obs-studio, obs-studio doesn't guarantee consistent A/V sync (and neither
does your video player, operating system, etc). For some audio codecs, even
video player restarts can alter A/V sync. Try PCM as the audio codec and
VLC as the video player.
OBS BotAPP* — *15:31
@Braith
If you are having problems with playing content created by OBS Studio in
Movies & TV or QuickTime Player, this is because the media player does not
have proper format support. This causes missing video, audio, or for the
file to not open at all. We recommend VLC Media Player
<https://www.videolan.org/vlc/> for better, accurate format support. Like
OBS Studio, VLC Media Player is a free and open source project.
Braith* — *15:49
Hello @Chiyo I find this happens over 5 to 8 minute cycles, from between
say three frames ahead to three behind over that time.
I would not say I need perfect sync, but within a couple of frames, and
something that does not have the additional variation caused by startup
changes.
I have considered other software, but have not found anything else like OBS
that can encode as MP4 like I would like it to.
I have been reviewing in Adobe Premiere frame-by-frame.
If you can suggest anything else, paid, or opensource free, I would be
interested, but so far have not found anything myself.
I use it to digitize VHS & other-format video tapes as a hobby-business,
but with near-museum/archive quality. I have been trying to find a way of
recording without needing to capture then process afterwards as most other
good-quality methods require.
I have been fiddling with this system for five years, and the audio sync is
the last (as far as I can see, though I have said it before!) issue.
I have considered contacting Ffmpeg as well?