adjusting brightness

[DeusExMachina]

A long standing issue has been the darkening of clips when encoding to MPEG-2 for DVD. Unfortunately the available filters do not seem to operate with the MPEG-2 encoder. Is there any work around to get appropriate brightness levels in the final encode? Since only ffmeg and mpeg2enc are available for conversion to MPEG-2, and neither of these allow brightness adjustment, am I stuck encoding to something else, then reencoding to MPEG-2?

[major]

The newest ffmpegX 0.0.9w r4 should handle filters with DVD mpeg2enc. The darkening may be linked to use of the option "Decode with Quicktime", try to disable it.

[DeusExMachina]

This is what I had understood; however, having checked both ways, I find that both qt and mplayer darken the file, though admitedly qt is worse.
I was hoping to avoid using mpeg2enc, since it seems to do a worse job at lower bitrates than ffmpeg. Is this not the case?

[major]

With mpeg2enc, you may also try to disable both "Decode with Quicktime" and "Decode with mplayer".

[DeusExMachina]

hmm… OK. I have a few questions then
1) what decoder will this default to
2) doesn't ffmpeg provide better quality at sub 4000 kbps
3) I assume you mean that I adjust luminance. What have you found to be a good value to get a result close to the original.

thanks

[major]

1) to ffmpeg decoder, 2) yes, ffmpeg is generally considered to encode at better quality, 3) I didn't experiment values, instead I'll provide an improved QT decoder for future versions of ffmpegX.

[DeusExMachina]

OK, sorry to appear dense!

Are you saying that if I select DVD mpeg2enc in the presets popup, and deselect both QT and mplayer in options, it will use ffmpeg to decode, and mpeg2enc to encode?

2) How will the quality compare to simply selecting the ffmpeg preset at sub 4000kps?

3) If I do this, would setting luminance to around 150 seem appropriate?

[rumplestiltskin]

1) to ffmpeg decoder, 2) yes, ffmpeg is generally considered to encode at better quality, 3) I didn't experiment values, instead I'll provide an improved QT decoder for future versions of ffmpegX.

Major,

Just wondering if this "improved" decoder will also help the H264 encoding (iPod). Just a thought.

Thanks for all you do!

[major]

OK, sorry to appear dense!

Are you saying that if I select DVD mpeg2enc in the presets popup, and deselect both QT and mplayer in options, it will use ffmpeg to decode, and mpeg2enc to encode?

Yes.

2) How will the quality compare to simply selecting the ffmpeg preset at sub 4000kps?

You should determine it perceptually, by encoding a clip in both ways and compare.

3) If I do this, would setting luminance to around 150 seem appropriate?

Sorry, but I didn't test values, as said above.

[major]

1) to ffmpeg decoder, 2) yes, ffmpeg is generally considered to encode at better quality, 3) I didn't experiment values, instead I'll provide an improved QT decoder for future versions of ffmpegX.

Major,

Just wondering if this "improved" decoder will also help the H264 encoding (iPod). Just a thought.

Thanks for all you do!

It will apply to all processes where the option "Decode with Quicktime" is used.

[DeusExMachina]

Hey Major.
Any ETA on that?

[DeusExMachina]

In adjusting luminance and saturation values in the mpeg2enc encoder, all I ended up with is washed out video. Nothing was able to actually increase overall brightness.

[rumplestiltskin]

I, for one, will welcome the improved QT decoder as I usually have video's that do not encode properly without using it. For example: The encoded video will become stark white about 15% through with the audio continuing just fine. Using the QT checkbox seems to prevent this problem.

[major]

Hey Major.
Any ETA on that?

It will be surely part of 1.0.0, maybe will be included before..

[DeusExMachina]

any hope for a beta in the meantime?

[major]

Yes, maybe it will be included before, I can't be more precise for now..

[DeusExMachina]

OK, so upon additional research, I am increasingly of the opinion that this is not a brightness issue at all, but rather one of gamma correction. Files originally encoded on a mac, or with Windows boxes with well calibrated gamma (I think there must be a few somewhere!) should appear just fine, but ones encoded on Windows or Linux boxes without gamma correction will re-encode dark.
First, is this correct?
Second, is there a way, possibly outside of ffmpegX, to adjust gamma of the clip prior to encoding so that the final output file appears correctly? Can I put the file in a quicktime envelope and edit the quicktime atoms, prehaps?

[rumplestiltskin]

You may adjust brightness and contrast with MPEG Streamclip.

[DeusExMachina]

Yes, but the problem is that you either have to re-encode, or only export to a file format other than mpeg2, since MPEG Streamclip is based on the Quicktime codecs, and Quicktime does NOT support MPEG2 encoding, and only does decoding grudgingly (like if you pay Apple to get their MPEG2 decoder, which I have.) Instead, Apple relies on Compressor (which I also have) which is so slow as to be useless, and which does NOT do a particularly good job at low bit rates.

[rumplestiltskin]

What is the format of the source video?

[DeusExMachina]

Sometime avi (DiVX mostly), sometimes ogm (containing whatever) a variety really.
It is not just me; it is a common complaint about encoding to MPEG-2. And since none of the open source codecs appear to allow gamma adjustment (or brightness) there is little to be done about it.
While the paid compression engines, such as Compressor (which I do have), can adjust values, they are terrifically slow and burdensome on system resources.
Still it would be interesting to know if I am correct in my suspicions about it being a gamma problem, since a fix would only involve tweaking the decode side.

[rumplestiltskin]

Sometime avi (DiVX mostly), sometimes ogm (containing whatever) a variety really...<snip>

You might try MPEG Streamcip to do an intermediate transcoding from AVI to AVI and adjust the brightness/contrast to taste. After that, do whatever you do to get to mpeg2. Can't help you with that as I abandoned mpeg2 and DVD (except for occasional iDVD use) and now stick with H264 for most everything. Of course, your needs are different than mine.

[DeusExMachina]

The low bitrates of my original files really preclude this, since the extra step in encoding will degrade video quality too much.

Gamma correction, anyone?

[DeusExMachina]

So after yet more research, it appears the issue IS the gamma setting. In particular, the codec supplied by Apple assumes a gamma of 1.8, which is fine, and how it should be, except that most DV codecs decode in a gamma=2.2 space. Although this is technically incorrect for RGB monitors, things are the way they are. Apple, being Apple, has chosen to ignore that, and seems to refuse to write the codec so that it even looks at the gamma value, instead just assuming playback on an Apple monitor, and ignoring any indication to the contrary. Any work-arounds would be greatly appreciated.

[rumplestiltskin]

Major is probably reading all of this so maybe the gamma issue (1.8 vs 2.2) will be addressed in the next release of ffmpegX. Frankly, I'd love to see it fixed, as well, because it would go that last step toward improving my H264/iPod transcodes.

[soholounge]

it amazes me that this mac/pc issue is still ongoing.
how did mac video people ever get by for all these years? (since the vast majority of end users are viewing on PC)
it just boggles my mind.

i use Cleaner, and the gamma correction works ok on that, but it still doesn't look "right" on PC's, looks a little bit washed out.

most of my source files are DV that i shot myself, so i just try to capture things brighter than i normally would...

with all the other issues, especially for mpeg-2, this dark/gamma issue is the least of my worries...

[rumplestiltskin]

I ripped one of my DVDs to HD then tried something different. I used MPEG Streamclip to export the VOBs (all at one time) to MJPEG-B and AIFF but bumped the brightness by 20% and the saturation by 30%. I then took the resulting file and used ffmpegX to transcode it to H264 for iPod (with my usual +30% video kbps and a Qmin/max or 3/28 - which is probably excessive but it provides exceptional results). The resulting H264 file looks great, almost exactly like the original DVD. I'll have to try this with some of the AVIs I get to see if this process (yes, it's longer and a PITA) works for them, as well. I'll advise.

[DeusExMachina]

This is not really a mac vs. pc issue. If the workflow is kept entirely on the mac, there is no problem, since the mac (correctly) sets the gamma value at 1.8. The problem arises on the PC where video that is captured or encoded has a gamma which is set at a value above 2, which the mac (for whatever reason) ignores.