Transcoding without changing image quality?

[Blatherscribe 5]

Sorry to trouble you again, but I'm still having subtitle problems. I know that at heart it's a Roku issue, since Roku doesn't support DVD/Blu-Ray subtitles, but I'm hoping there's a way to work with Emby's side of things.

 

The problem I'm having is that if I turn on transcoding, I always lose image quality. I have the option to extract subtitles on the fly checked, but the Emby server still seems to reduce the image quality, I guess to save bandwidth. I have plenty of bandwidth on my LAN. Is there a way to turn off that aspect of transcoding? *ONLY* extract subtitles, without changing anything? I've tried, and I can't seem to find a setting that does the trick. Many of my files are from DVDs, or Blu-Rays of older shows, so even a slight decrease in quality is noticeable.

 

I've used Open Subtitles, and those work, but they're sometimes inaccurate and always seem to be out of sync with what's on the screen. I'm using a couple of programs to extract the subtitle tracks and then OCR them, but that is the work of ages, since I have to shepherd each OCR edit.

 

Any suggestions? Thanks!

 

[Luke 42079]

Hi there, can we please look at an example? Please attach the information requested in how to report a media playback issue. thanks !

[Blatherscribe 5]

Sure, I've just gone and briefly played an episode. Log attached here. Thanks!

 

Also, I almost forgot to ask: if I extract the subtitle tracks, is there a way to get Emby to use the .sub files without having to OCR them into text?

embyserver.txt

Edited October 23, 2019 by Blatherscribe

[ebr 16184]

Hi.  Was there also an ffmpeg log?

[Blatherscribe 5]

Sure, here's one. Thanks for looking into this.

 

Also, if I may ask, how does Emby handle these subtitles? Is it just much, MUCH better OCR than the subtitle editor I have? I ask because these subtitles don't have the appearance I set up under my profile, and they're not riddled with minor inaccuracies. Definitely preferable, if I can get them extracted without changing the image quality.

[ebr 16184]

Hi.  Did you forget to attach the file?

[Blatherscribe 5]

I'm sorry, I was certain I'd pushed all the buttons. Must not have. Here it is for real (I think).

ffmpeg-transcode-0a0c9b70-bb9a-47ff-b05a-82bbe1f75deb_1.txt

[ebr 16184]

Hi.  It is not extracting subtitles, it is burning them in because they are graphic subs (PGS) that the Roku cannot display.  This shouldn't involve much quality loss but I guess that really depends on a lot of factors.

 

The best thing to do would be to use our subtitle download capability to obtain text based subs that won't require burning in.

 

Please let us know if this helps.

 

Thanks.

[Luke 42079]

How much worse do you feel it is?

[Blatherscribe 5]

It seems to depend on the show. I've tried it with a few shows so far. With movies, I don't notice a difference, but strangely with Star Trek: Enterprise I do. Live-action shots seem about the same, but fast action and CGI looks slightly fuzzy, which goes away with direct streaming.

 

When burning in the subtitle image, does Emby change the image quality? If you say it doesn't, I'm willing to accept that my perceptions are what's flawed. I do my best to be objective, but since I have no way to do a double-blind test, it's always possible the problem is between the chair and the computer, or in this case the TV.

[Luke 42079]

When burning in the subtitle image, does Emby change the image quality? If you say it doesn't, I'm willing to accept that my perceptions are what's flawed. I do my best to be objective, but since I have no way to do a double-blind test, it's always possible the problem is between the chair and the computer, or in this case the TV.

 

No, we don't change the quality, however that doesn't necessarily mean the transcoder will produce an identical result, but it shouldn't be worlds apart though either.

[Blatherscribe 5]

Would the hardware acceleration one can enable with a premiere membership bring the result closer to the original? (Last question, I promise.)

[Happy2Play 9780]

The log above show a maxbitrate equal to the original media (6519672) set in the ffmpeg commandline but would appear the media never achieved more then 1424.3kbits/s.

 

 

C:\Users\kdl\AppData\Roaming\Emby-Server\system\ffmpeg.exe -ss 01:34:54.000  -f matroska -i file:"D:\Videos\Movies\The Mummy (1999).mkv" -threads 0 -map 0:0 -map 0:1 -c:v:0 libx264 -copyts -filter_complex "[0:2]scale=1920:816:force_original_aspect_ratio=decrease_{;[0:0]overlay=(W-w)/2:(H-h),scale=trunc(min(max(iw\,ih*dar)\,min(1920\,1080*dar))/2)*2:trunc(min(max(iw/dar\,ih)\,min(1920/dar\,1080))/2)*2" -pix_fmt yuv420p  -maxrate 6519672 -bufsize 13039344 -preset veryfast -profile:v:0 high -level:v:0 4.1 -crf 18 -x264opts:0 subme=0:me_range=4:rc_lookahead=10:me=dia:no_chroma_me:8x8dct=0:partitions=none -g:v:0 72 -keyint_min:v:0 72 -sc_threshold:v:0 0  -vsync -1 -codec:a:0 copy -metadata:s:a:0 language=eng -disposition:a:0 default -f segment -max_delay 5000000 -avoid_negative_ts disabled -map_metadata -1 -map_chapters -1 -start_at_zero -segment_time 3  -individual_header_trailer 0 -segment_format mpegts -segment_write_temp 1 -segment_list_type m3u8 -segment_start_number 1898 -segment_list "D:\Videos\Temp\transcoding-temp\139e208471c9c2350cce72746a5aba0c.m3u8" -y "D:\Videos\Temp\transcoding-temp\139e208471c9c2350cce72746a5aba0c%d.ts"}

elapsed=00:02:23.18 frame=43138 fps=301 q=-1.0 Lsize= 1302815kB time=02:04:53.22 bitrate=1424.3kbits/s dup=0 drop=1 throttle=off speed=52.3x

[Blatherscribe 5]

Would hardware acceleration help with that? Or is it impossible to reach the original bitrate? I know transcoding from the original DVD rips took slightly longer than the runtime of the video.

[Luke 42079]

No, you can try lowering the server transcoding setting called CRF, as well as changing the h264 preset. Keep in mind though, we really suggest using the defaults as they are optimized for streaming. But you can try changing those values.

[Blatherscribe 5]

OK, I've reset the CRF to the default. I had it on 18, which is what I used when transcoding from the originals. I'll see if this helps.

 

Thanks again! I really appreciate you taking the time to go through all of this.

[ebr 16184]

OK, I've reset the CRF to the default. I had it on 18, which is what I used when transcoding from the originals. I'll see if this helps.

 

Thanks again! I really appreciate you taking the time to go through all of this.

 

Okay, so you had changed this from the default.  Please report back if the default setting works better for you.

 

Thanks.

[Blatherscribe 5]

It didn't. It seems about the same, possibly a touch worse. I think the problem isn't with Emby, it's with the Roku device. Asking Emby Server to transcode on the fly and produce the same quality I have saved on my hard drive isn't reasonable. It took about 150% of runtime to transcode these in the first place, so I can't imagine getting the same quality fast enough to do it as the film plays.

 

I think the solution will be to buy an Amazon Fire TV stick the next time they're on sale -- assuming what I read online is correct, that they can display DVD and Blu-Ray graphical subtitles. Then I can stream at full quality and make my wonky eyes happy.

 

Thanks again for helping!

[Luke 42079]

A lower crf means higher quality so the default should be worse than what you had before.

[ebr 16184]

It didn't. It seems about the same, possibly a touch worse. I think the problem isn't with Emby, it's with the Roku device. Asking Emby Server to transcode on the fly and produce the same quality I have saved on my hard drive isn't reasonable. It took about 150% of runtime to transcode these in the first place, so I can't imagine getting the same quality fast enough to do it as the film plays.

 

I think the solution will be to buy an Amazon Fire TV stick the next time they're on sale -- assuming what I read online is correct, that they can display DVD and Blu-Ray graphical subtitles. Then I can stream at full quality and make my wonky eyes happy.

 

Thanks again for helping!

 

Simply obtaining text based subs can solve your problem too.  Emby can even help you find them.

 

Automatic Subtitle Downloads

Manual Subtitle Downloads

[Blatherscribe 5]

Thanks, I appreciate the suggestion, and I did that using Open Subtitles. The problem is that they're always slightly out of sync with the dialogue. And it isn't consistent: in the same show, subtitles will precede dialogue in some parts, follow it in others. The official subtitles don't do this, which is why I'm searching for solutions that will make them work.

[Luke 42079]

There are tools out there that can extract them and try to convert them to plain text.

[Blatherscribe 5]

Thanks, I do appreciate the advice. I already have that, but the problem is the OCR is unreliable, and it would be the work of ages to run every single video I have through that process, scanning everything for errors. That's why I was hoping there was a solution that would do the job without lowering the image quality. But I understand better now how that process works, and there's no way to keep precisely the same image quality when transcoding.

[Luke 42079]

Yes It's a trade-off. Thanks for the feedback.

[Blatherscribe 5]

In case it sounded in any way like a complaint, my feedback is that your program is excellent, you and the rest of your team are incredibly helpful, and this is down to Roku not having been designed for this purpose.