frame rate & aspect ratio

[hgurol]

I have been converting videos for many years with same very minimal and basic knowledge. Not as a pro but just here and there where needed. Now, Im gonna start working for a project and I will be converting 25-30 video files a week to be streamed on the internet. I thought this is the time that I need to improve my basic knowledge.

Aspect Ratio:
When Im encoding video I never change the aspect ratio, I just leave as what the original source is. Even sometimes the source comes with a weird, non-standard aspect ratio and even if I intend to change it to a standard value I just dont because Im scared that it will have a negative effect on the file size, encoding time and picture quality. What is the real relation of Aspect Ratio on these things? Is what I seem to know the truth or just a myth? If I really do not get a penalty for changing the aspect ratio I would love to change it to some well known standard values.

Frame Rate:
The same goes for the frame rate as well. I never change it and keep the original file's frame rate intact. Sometimes I think that I would have an advantage on the file size if I convert a 30fps source to 23fps, but then again for the same reasons above, not to increase the processing time and lower the picture quality, I never change this value as well.

I have no idea how accurate my knowledge on this issues. I will be very happy if you can shed some light on these topics.

Thank you...

[BaaGGHo]

How much frame's rate?
me looking for nice expensive frames for family 8"×12" pics.

[hgurol]

How much frame's rate?
me looking for nice expensive frames for family 8"×12" pics.

Free for you.

[BaaGGHo]

how many you have?
me need around 15, will pay postage.

[Cornucopia]

Do the LEAST HARM! So that means don't re-encode unless you have to, etc.

That said, it is much better to stick to STANDARDS. This applies to frame sizes (resolution), framerates, colorspaces and codecs.

Sounds to me like you've got a number of downloaded crap from wherever (from people who probably don't really know what they're doing or why).
For compatibility-sake, IIWY, I'd do a single re-encode to standard settings. This actual setting will depend on what you output your stuff to (media player, etc) and/or plan on for the future. A good baseline is 720p or 1080p h.264 video in MP4 container with decent bitrate for your material.

If you live in PAL-lands, you should have 24fps (film-based) or 25fps (video-based) material. If you live in NTSC-lands, you should have 24/23.976 fps (film-based) or 29.97 fps (video based) material.

If it ends up 720p or 1080p, AR is then easy, because it should be 16:9 DAR (use letterboxing if necessary) and 1:1 PAR.

Scott

[PuzZLeR]

Some of my suggestions: Only re-encode when necessary, as mentioned, such as to fit a profile/standard or clean something up with cropping or filtering.

Aspect Ratio: Keep in mind the difference between Display Aspect Ratio (DAR) and Pixel Aspect Ratio (PAR). You can manipulate the aspect ratio if you understand what is happening with the PAR as to not distort the picture. You can keep an eye for black banding, crop, or even add it if you want to fill a standard or profile. It all depends on your Source.

Frame Rate: You really have to know what you're doing here. The most typical cases I run into are indeed taking 29.97fps content that is if, and only if, it is film source and converting it to 23.976fps to save file size. Or when I speed up 24fps to a 25fps PAL profile, or similarly in reverse for NTSC, etc (but taking care to watch interlacing and adjusting accompanying audio speeds as well). Each is a lecture or mini-guide on its own, so you will have to do a little research on these.

I do have the same belief as Cornucopia in what people may be giving you. I personally do video work for others - for a price - for an audio firm's clients, and from experience you will find (frustratingly so) that many people have no clue about video and have HUGE expectations. They will throw dirty water at you and expect you to turn it into wine, since you're the "expert".

I've even had people give me VHS tapes of 30 year old EP analog cable recordings and expect it on blu-ray. Of course this is possible, but they have expectations that it will look as good as any 2012 movie production. Really!

Good luck.

[hello_hello]

Personally, unless I'm converting video specifically to create a complaint DVD or Bluray video disc, I don't worry about standard aspect ratios.
If the video in question has a display aspect ratio of something other than 4:3 or 16:9, it's probably been re-encoded while cropping any black bars. Standard DVD/Bluray 16:9 and 4:3 display aspect ratios include any black bars. If they're removed when encoding, what's left (the actual picture area) will of course have a different display aspect ratio (maybe around 2.35:1 or 2.40:1 etc).

If you're converting to a file type such as MP4, MKV or AVI etc, and your player is capable of playing the converted video, it'll do so whether the black bars have been removed when encoding or not. If they've been removed, the player will add them back on playback. If you're converting to a DVD or Bluray video format using software designed for that specific task, then chances are if the display aspect ratio is something other than 16:9 or 4:3, the conversion software will simply add them back while it's encoding to produce complaint 16:9 or 4:3 DVD/Bluray video. Generally if encoding software offers an aspect ratio after you've opened a video, it's showing you the display aspect ratio of the source video. You generally don't won't to touch it unless the encoding software gets it wrong (which should hardly ever happen) and the encoded video looks distorted, or you know the aspect ratio of the source video is incorrect and want to fix it while re-encoding.
Also when converting to create complaint DVD/Bluray discs, the video may need to be resized to standard DVD/Bluray video dimensions, but any decent DVD/Bluray encoding software should take care of that for you without distorting the picture.

Basically..... as long as the shape of objects in the encoded video look identical to the original video, then the "picture" aspect ratio hasn't been changed, which is what you want.

As high def and standard def video use a slightly different colorometry it's generally wise to convert the colors when converting from HD to SD (or from SD to HD) however I'm not sure if converting software does so automatically as a rule. Software designed for creating DVD complaint video might (I'm not sure) but none of the standard Xvid/x264 encoder GUIs I've used do. The color difference isn't huge but as I do a lot of encoding it's enough to annoy me, so I use encoder GUIs which at least let me add color conversion manually if need be.

Frame rate: If the video is 29.970 "NTSC" then it's interlaced and while it can be de-interlaced it'll always be 29.970. If the video is really 23.976 "Film" it'll use repeated fields to change the frame rate from 23.976 to 29.970 and can be (and probably should be) converted back to 23.976 when encoding. Some video can be a combination of the two. Decent conversion software will analyze the video and automatically apply de-interlacing or inverse telecine etc, although they don't always get hybrid video 100% right 100% of the time. I'm not anything close to being an NTSC expert as I live in Pal-land and PAL video is much easier. It's either progressive 25fps or interlaced 25fps.

[hgurol]

I'm gonna start converting 25-30 video files per week. Yes, they are crap downloaded from internet and the bad news is, some of them are prepared by people who knows even less than I know about video conversion. And I would say I'm a beginner as well. I have no control about finding, choosing or selecting the video files myself. They will be provided to me. I will be converting them and upload them to a website for streaming. I have already choose to use H.264 & AAC as my codecs. I'm not expected to bring a standard for the files, nor to change the aspect ratio or the frame rate. I'm expected to find a good balance between the file size and the picture quality. I'm not expected directly but of course the time I spend with each conversion process is also important for me.

However, since some of these files are really crap, no standards are followed, I would feel like I wont be doing my job properly If I don't fix some of them. I have a 28fps video file, never heard of a 28fps before. And some aspect ratios which is not standard or some very rarely used ones.

Part of myself says; I should come up with 3-4 different standards of my own, of course which would match with the well known standards of the video industry. Maybe 2 for all different variations of wide screen sources to lock them to 16:9 and 2 for the all non-wide screen variation sources to lock them to 4:3. And a frame rate of 24 or 25 for all of them (up or down). And when I'm converting the files I should choose one profile of my own pre-defined ones.

Well, the other part of myself says; do not touch the frame rate and aspect ratio If you don't want any trouble.

From what you have said; I understand that changing the frame rate is not as easy as it sounds. I should take into account of syncing the audio and such. As for the aspect ratio, I should take the PAR into account to avoid distortion and stretches. But as goes my original question, I would not get any penalty on the file size and the picture quality If I do these changes properly. Right ?

As for the conversion time, I believe the process will take a lot longer, maybe will double, when I change the AR and FR compared to when I don't touch them. Is that right?

I'm not asked for all these standardizing but I really wanna do this thing properly, only If it doesn't brings me too much headache

Thanks

[hello_hello]

If you're converting video for a web site, while I don't know if it's mandatory, I guess sticking to a few standard resolutions (720p, 480p etc, using a predetermined width for each resolution), and all with a nice 16:9 (or 4:3) aspect ratio, would at least be a better "look".

You'd probably want to convert any video using non-square pixels to square pixels, add any black bars or letterboxing back if necessary to keep nice 16:9 or 4:3 aspect ratios.

Using a decent encoding program should make resizing fairly easy. Mostly you'd to pick a new video width yourself, then let the program work out the appropriate height for you. From there it's just a matter of adding back the black bars if need be, which is not something I've ever done myself, but shouldn't be too hard.

Changing the aspect ratio or resizing shouldn't effect the encoding time very much, and if you're resizing down considerably it'd probably speed it up as there's less video to encode. Changing the frame rate isn't something I do much, but there's a few ways to do it.... from simply speeding it up or slowing it down to various methods of changing it without changing the video duration. AviSynth has a detailed explanation on the methods it uses for frame rate conversion here http://avisynth.org/mediawiki/AssumeFPS, which might help explain the various ways of doing it.
I don't think you'd necessarily increase encoding time too much, but unless you've got a specific need to change the frame rate.... well if people are generally going to be viewing the video on a PC, then I wouldn't bother.

Aside from my armchair opinioning, there's a forum here dedicated to video streaming. If that's your goal, you might be better off trying there for tips and trick on encoding video for streaming. I don't spend any time there myself, but hopefully you'll find knowledgeable people on the subject. https://forum.videohelp.com/forums/48-Video-Streaming