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Main Concept H.264 Issues with 23.976

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Andrew Saliga
Main Concept H.264 Issues with 23.976
on Mar 5, 2010 at 8:07:53 pm

Trying to encode some H.264s with the Main Concept encoder using Sorenson 6 on a PC and a Mac.

The source is ProRes422HQ, 23.976fps, 1280x720. Framerate settings on the encoder are 1:1, and I've also tried forcing 24fps. Either way it's coming out at 23.952.

I searched Sorenson's forums (which aren't that great) and didn't find any solutions. Has anyone else had this issue?

It seems to be a MC issue since when I encoded the same file in Sorenson using Apple's H.264 encoder it came out at 23.976 as it should. To add to the situation, when I encode 1 second of the 30 second spot it with MC it comes out correctly, but if I do the whole :30 it's back to 23.952fps.

-Andrew Saliga

Steelehouse Productions
http://www.steelehouse.com (undergoing a much-needed redesign)
http://www.vimeo.com/steelehouse


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Daniel Low
Re: Main Concept H.264 Issues with 23.976
on Mar 5, 2010 at 8:22:35 pm

What are you using to report the frame rate?

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Andrew Saliga
Re: Main Concept H.264 Issues with 23.976
on Mar 5, 2010 at 8:25:09 pm

MediaInfo

QT7 Pro says 23.952 as well.

-Andrew Saliga

Steelehouse Productions
http://www.steelehouse.com (undergoing a much-needed redesign)
http://www.vimeo.com/steelehouse


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Daniel Low
Re: Main Concept H.264 Issues with 23.976
on Mar 5, 2010 at 8:48:46 pm

[Andrew Saliga] "It seems to be a MC issue since when I encoded the same file in Sorenson using Apple's H.264 encoder it came out at 23.976 as it should"

I hear what you're saying, however I'd have to say it's more than likely the Squeeze implementation of the MC SDK that's the problem, as there are other transcoders and encoders (Carbon Coder, Anystream etc) than use the MC SDK that don't suffer from this problem. AFAIK.



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Andrew Saliga
Re: Main Concept H.264 Issues with 23.976
on Mar 5, 2010 at 8:57:51 pm

Hmmm. Good to know Daniel.

I'll take it up with Sorenson in that case, and post back if any progress is made.

-Andrew Saliga

Steelehouse Productions
http://www.steelehouse.com (undergoing a much-needed redesign)
http://www.vimeo.com/steelehouse


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Andrew Saliga
Re: Main Concept H.264 Issues with 23.976
on Mar 11, 2010 at 5:44:54 pm

Still working with Sorenson on this, but here is the latest info I sent them. Maybe this will let someone else know that there is an issue or maybe someone has a solution.


"All source video is exported from After Effects and has the following specs:

* ProRes 422 (HQ)
* 1280x720
* 23.976fps
* 2 of the 4 had audio at MP3, 48KHz, Stereo

The two with audio came out at 23.976 as they should, but the two without audio came out at 23.95. Thinking that it may be an audio-related issue, I re-encoded the file that was initially causing problems. It also is ProRes 422 (HQ) file from AE. 1280x720, 23.976fps. It comes out at 23.952fps.
"

-Andrew Saliga

Steelehouse Productions
http://www.steelehouse.com (undergoing a much-needed redesign)
http://www.vimeo.com/steelehouse


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Andrew Saliga
Re: Main Concept H.264 Issues with 23.976
on Mar 17, 2010 at 3:23:12 pm

Squeeze support was working back and forth with me though email, but hasn't said anything in 5 days.

If anyone has any insight or jabs in the dark it would be appreciated.

-Andrew Saliga

Steelehouse Productions
http://www.steelehouse.com (undergoing a much-needed redesign)
http://www.vimeo.com/steelehouse


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Larry Little
Re: Main Concept H.264 Issues with 23.976
on Apr 10, 2010 at 11:59:40 pm

Did you even find out anything further on this?

Just to make sure I understand, it's playing "normally," just at a slightly slower framerate, correct? (i.e. it's not actually dropping frames or showing any sort of visible playback issue, correct?)

Out of curiosity, did you try any other framerates just as a troubleshooting step to see if OTHER encoded framerates are effected by a similar bug, or if it's just the ones around 24fps? It may help point to a where the glitch is actually happening.

When I'm faced with this sort of issue, I start trying other settings just to see if I can isolate the issue. For example, you might want to try an encode without audio, or perhaps with audio set to 44.1 instead of 48 just to see what happens. Sometimes a seemingly disconnected setting can end up being the culprit.

Larry



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Andrew Saliga
Re: Main Concept H.264 Issues with 23.976
on Apr 12, 2010 at 2:55:28 pm

I wouldn't call it dropping frames since it's not doing so out of error or in order to playback smoothly. The framerate is lower than what it should be though, and it shows in playback. I doubt they untrained eye would notice, but the our motion graphics buy and myself noticed it.

I've isolated every possible culprit one at a time and have been working with Sorenson support for a few weeks. Turns out there is a software bug in Squeeze when you add b-frames to a 24fps video it has problems outputting the correct framerate. The addition of b-frames is what causes the glitch. The tech support guy I spoke with said he's submitted it to the engineers and an update will be released.`

-Andrew Saliga

Steelehouse Productions
http://www.steelehouse.com (undergoing a much-needed redesign)
http://www.vimeo.com/steelehouse


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Larry Little
Re: Main Concept H.264 Issues with 23.976
on Apr 12, 2010 at 9:35:50 pm

Glad you got it solved (or are at least on the right path.)

I'm NOT downplaying the importance of getting this issue fixed, but I'm curious -- can you REALLY "see" the difference in speed, which is only .1%? It's only a .024fps difference, which is exactly the same fps difference as 24fps vs 23.976fps, which most people consider utterly undetectable. That's only a single frame slow after 41.7 seconds. Again, I fully agree that this needs to be fixed -- I'm simply astonished that anyone could actually SEE the difference visually.

By the way, it may be significant that the difference you're seeing IS exactly the same as 24 to 23.976 (i.e. a .024fps difference.) I thought that this might help point to the issue -- i.e. maybe Squeeze is automatically applying some sort .024fps "correction" thinking that this is needed to create a 23.976fps output instead of 24fps. It just seemed interesting that the fps difference was exactly the same as 24 vs 23.976.

Larry



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Andrew Saliga
Re: Main Concept H.264 Issues with 23.976
on Apr 15, 2010 at 8:01:04 pm

I appreciate the logic Larry.

I agree that this difference shouldn't be noticeable, but there is something about the way that Sorenson is removing frames that adds a slight jitter to the video.

I know it's not just me because I was showing a compression to one of our motion design guys to show him the amount of color I was able to retain with one H.264 encoder over another. He has no idea that there was a framerate issue, and that was the first thing that he noticed. It's subtle, but, as I said, it seems to be more than just less frames, it's the way those frames are removed.

That is an interesting note on the fps difference. Sounds like it has to be the issue.

-Andrew Saliga

Steelehouse Productions
http://www.steelehouse.com (undergoing a much-needed redesign)
http://www.vimeo.com/steelehouse


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Larry Little
Re: Main Concept H.264 Issues with 23.976
on Apr 16, 2010 at 12:19:58 am

I agree that this difference shouldn't be noticeable, but there is something about the way that Sorenson is removing frames that adds a slight jitter to the video.


Ah -- now THAT I can understand seeing! I totally misunderstood what you were saying. I thought you were saying that it's simply playing the same number of frames at a slightly slower speed -- i.e. that the entire movie takes just a tad longer to complete. You're saying, however, that it's actually DROPPING frames in order to "convert" the original framerate to 23.952fps.

Yes -- that's definitely something you could see since missing frames can be quite noticeable.

If Sorenson needs a better test to demonstrate what's happening, just give them something with timecode burn-in, or perhaps some sort of leader with even movement in it, so they can actually see the number sequence skipping over frames.

Please keep us posted on what happens,

Larry



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Andrew Saliga
Re: Main Concept H.264 Issues with 23.976
on May 5, 2010 at 6:19:46 pm

Sorry, this has kind of been lingering. It came to my mind again today when I encountered this issue again.

Six different 30 second commercials, all 1080p, 29.97, ProResHQ. Without rhyme or reason, 3 of the 6 defaulted to various odd framerates. I had thought at time it was when using the MC H.264 encoder on content with audio and encoding with B-frames, but it seems that it's not so predictable.

The latest I've from Sorenson is a major update coming out in June or July.





-Andrew Saliga

Steelehouse Productions
http://www.steelehouse.com (undergoing a much-needed redesign)
http://www.vimeo.com/steelehouse


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