720 x 576 question

[higgins327]

Hi all!

I'm ripping VHS tapes and I get files that measure 720 x 576 pixels. I thought that was 4:3, but it's not, and I'm confused how I should act. This is raw data and I'm re-encoding it anyway. Should I resize the video to 720 x 540 to get the correct aspect ratio?

My goal is to get size efficient .avi files that I can store on my PC. Perhaps I set up a PC as a media centre in the future or get an XviD compatible standalone player to watch the rips.

What should I do with the files?

[hech54]

PAL

Video:
Up to 9.8 Mbps* (9800 kbps*) MPEG2 video
Up to 1.856 Mbps (1856 kbps) MPEG1 video
720 x 576 pixels MPEG2 (Called Full-D1)

[higgins327]

So, the 720 x 576 is the correct aspect ratio despite not being 4:3?

[hech54]

720 x 576 is correct.

[Case]

The dimensions of the 720x576 capture are good; it is the same for DV and DVD.
The frame size is independent of aspect ratio, that is, it will be sized (stretched) to 4:3 on playback.
Broadcast (DVB, DV, DVD, VHS capture) can be considered as having rectangular (non-square) pixels, so that 720x576 becomes 4:3 (or 16:9).

However, AVI does not have good support for such aspect ratio control. Many players will assume a PAR of 1:1 for AVI. Resizing to 720x540 when converting to XviD would guarantee proper 4:3 playback.

Another thing to think about is the interlaced nature of VHS. If you convert and scale to a progressive AVI, then you may get some artefacts from less-than-optimal de-interlacing.

I think MP4 would be more future-proof, as MP4 allows for interlaced content and aspect ratio control at the capture resolution, thus keeping the information that you captured.

[higgins327]

Resizing to 720x540 when converting to XviD would guarantee proper 4:3 playback.

That's what I was thinking. If I view the 720x576 video later, I need to set the aspect ratio to 4:3 via the media player interface.

I've also heard that the reason for this weird ratio is correct because pixels aren't square, but rectangular.

[higgins327]

I think MP4 would be more future-proof, as MP4 allows for interlaced content and aspect ratio control at the capture resolution, thus keeping the information that you captured.

That's a bit technical for me.

You mean that I should convert the file to mp4 instead of avi, or that I should try to capture it in mp4 format?

[Gavino]

Resizing to 720x540 when converting to XviD would guarantee proper 4:3 playback.

Another thing to think about is the interlaced nature of VHS. If you convert and scale to a progressive AVI, then you may get some artefacts from less-than-optimal de-interlacing.

Precisely because of this interlaced nature, resizing to 720x540 is wrong and will give artefacts, as an interlaced source cannot be vertically resized without first deinterlacing (or using some special interlace-aware resizing technique).

If you want to convert to square pixels, you should resize horizontally to 768x576.
(Actually, to be more correct, you should normally crop centrally to 704x576 and resize that to 768x576.)

[higgins327]

(Actually, to be more correct, you should normally crop centrally to 704x576 and resize that to 768x576.)

Why the cropping beforehand? Especially if I don't have the black edges... or if I have the black bar on one side of the screen only (I sometimes do).

[Case]

I think MP4 would be more future-proof, as MP4 allows for interlaced content and aspect ratio control at the capture resolution, thus keeping the information that you captured.

That's a bit technical for me.
You mean that I should convert the file to mp4 instead of avi, or that I should try to capture it in mp4 format?

In my opinion, you should convert to MP4 instead of AVI, if your encoder app allows for interlaced MP4. You would also keep the original resolution 720x576, and set a 4:3 DAR flag (or corresponding PAR flag). That way you don't lose detail from resizing or de-interlacing.

[Gavino]

Why the cropping beforehand? Especially if I don't have the black edges... or if I have the black bar on one side of the screen only (I sometimes do).

The 4:3 ratio is defined by the standards to apply to the 704 pixels of 'active width'.
Usually with VHS you find you only have 704 useful pixels anyway, although they are not always central to the image, eg you might need to crop 4 off one side and 12 off the other, instead of 8 on each side. (Certainly, any cropping should always be in even numbers.)

[higgins327]

I use Pinnacle PCI-700 card (and Studio 9) for capturing and then re-encode (and cut the commercials) using VirtualDub. Neither supports mp4. Also, XviD is supported by most standalone players. Are there any devices except iPods that support the mp4?

Edit: So, basically what you're saying is that if I convert to MP4 instead of AVI, I don't need to worry about reconverting to the actual aspect ratio -- I can just open the file in some editor and set the correct aspect ratio without re-encoding anything? That sounds pretty sweet.

[hech54]

Another "bombarding the newbie/rookie" thread.

[higgins327]

I want to try that new format out. What's the VirtualDub equivalent for editing MP4 files?

[yoda313]

I want to try that new format out. What's the VirtualDub equivalent for editing MP4 files?

You should be able to open the mp4 in virtualdub. Use directshowsource avisynth filter to open it (its in a little drop down window in the open file dialog box).

Otherwise use avidemux and you should be ok.

edit

Virtually anything plays mp4 these days - so long as its h264 or divx/xvid inside the mp4. And most portable players need smaller resolutions like 320x240 in order to play it back.

And it needs to be unencrypted - it can't be a store bought video - those can only be directly played back on the authorized players that particular online service supports.

[higgins327]

Since the thread is pretty much mixed anyway... how can I change the mp4 aspect ratio flag in avidemux?

[lordsmurf]

I think MP4 would be more future-proof.

No.
MPEG-4 wrapper is generally used for long GOP high compression formats -- not captures.
MPEG-4's future is uncertain in the face of wrappers like MXF, and HTML5.

MPEG-4 is not a "format".

[edDV]

Hi all!

I'm ripping VHS tapes and I get files that measure 720 x 576 pixels. I thought that was 4:3, but it's not, and I'm confused how I should act. This is raw data and I'm re-encoding it anyway. Should I resize the video to 720 x 540 to get the correct aspect ratio?

My goal is to get size efficient .avi files that I can store on my PC. Perhaps I set up a PC as a media centre in the future or get an XviD compatible standalone player to watch the rips.

What should I do with the files?

Lets start over.

1. How does one "rip" analog VHS tapes? Analog PAL tapes have 625 total horizontal lines but only 576 are in the active video frame..

2. If you want to A/D capture 4:3 square pixels, you would purchase a capture card capable of 768x576. Those are uncommon. Most consumer capture cards follow DVD resolution (ITU-Rec601) 720x576* with non-square (rectangular) pixels.

3. Digital broadcast SD video is just like DVD, that is 720x576 but you are capping VHS tapes so ignore that for now.

4. "AVI" files is unhelpful. AVI is a container spec and has nothing to do with resolution. "Xvid" or "Divx" are codecs that some convert to after 720x576 capture. There are several ways to convert 720x576 to square pixels. The way DVD players or digital TV sets do this is apply a horizontal scale to 768x576 for 4:3 or 1024x768 for 16:9. This preserves interlace. Interlace is fine for DVD or DVB MPeg2. Also AVC or VC1.

5. Unfortunately, your choice of the Xvid codec is both DVD and interlace unfriendly. Xvid is more a hacker computer nerd format. Computer nerds are interlace phobic and don't even begin to comprehend rectangular pixels. Their reaction to 720x576i capture files is like a little girl seeing a mouse. They cry Eeekkkh! Then they insist on destructive deinterlace, then squish the hulk into square pixels. Some like 720x540 for 4:3 aspect ratio, some like 720x405 for 16:9. But digital video fights back unless resize divides into 16x16 blocks. Fellow geeks laugh at newbies for choosing 720x540 or 720x405.

I'll stop for questions.


* most consumer capture cards capture 720x576 but active PAL video line length is only 702 pixels wide when sampled at 13.5 Ms/s. As a result 720x576 capture will pick up 9 pixels of black blanking left and right.

[higgins327]

Thanks for a through reply!

1. How does one "rip" analog VHS tapes? Analog PAL tapes have 625 total horizontal lines but only 576 are in the active video frame..

I use Pinnacle PCI-700 card (and Pinnacle Studio 9) for capturing and then re-encode (and cut the commercials) using VirtualDub.

3. Digital broadcast SD video is just like DVD, that is 720x576 but you are capping VHS tapes so ignore that for now.

Let's not ignore it. I have digital broadcast recordings also. My receiver records PVR files which I rename to TS and then convert to AVI (XviD;mp3) using FormatFactory (the only way I know to do it, easy to use for batch converting). Then I use VirtualDub to cut out commercials. I have no idea whether that breaks interlacing or not. I read the wiki article on interlacing, but frankly, I'm still confused what that exactly means -- except that broadcasters like it for technical reasons and it produces the combing effect.

2. If you want to A/D capture 4:3 square pixels, you would purchase a capture card capable of 768x576. Those are uncommon. Most consumer capture cards follow DVD resolution (ITU-Rec601) 720x576 with non-square (rectangular) pixels.

Point is, I don't know what I want. That's essentially what I'm asking here.

4. "AVI" files is unhelpful. AVI is a container spec and has nothing to do with resolution. "Xvid" or "Divx" are codecs that some convert to after 720x576 capture. There are several ways to convert 720x576 to square pixels. The way DVD players or digital TV sets do this is apply a horizontal scale to 768x576 for 4:3 or 1024x768 for 16:9. This preserves interlace. Interlace is fine for DVD or DVB MPeg2. Also AVC or VC1.

So, if I want to watch this file on a television set or a DVD player (I'm assuming you mean standalone player with XviD support, not converting to straight DVD), then I should keep the 720x576, but if I want to view the files on the PC, I should change it to 768x576?

5. Unfortunately, your choice of the Xvid codec is both DVD and interlace unfriendly. Xvid is more a hacker computer nerd format.

I've chosen XviD because:
- I have no intention of producing full blown DVDs. I don't find "one movie per disc" size efficient (especially considering the VHS-rip or digital non-HD capture quality) and DVDs are completely unreliable in my experience (I have several Verbatim discs that are unreadable after just a few years).
- XviD is supported by standalone DVD players (should I ever get a better one than I currently have). I have no intention of buying PSP or Xbox.
- XviD is the only codec I've managed to get working properly (though that may be VirtualDub issue -- and I'm considering on moving to Avidemux, especially if MP4 container makes it possible to set aspect ratio flags without re-encoding the whole file).

Computer nerds are interlace phobic and don't even begin to comprehend rectangular pixels. Their reaction to 720x576i capture files is like a little girl seeing a mouse. They cry Eeekkkh! Then they insist on destructive deinterlace, then squish the hulk into square pixels. Some like 720x540 for 4:3 aspect ratio, some like 720x405 for 16:9. But digital video fights back unless resize divides into 16x16 blocks. Fellow geeks laugh at newbies for choosing 720x540 or 720x405.

I did a quick survey and most my videos are 720x576. I didn't notice the aspect ratio difference until recently -- now I do, and I need to set the aspect ratio to 4:3 via VLC interface every time I watch something and it's cumbersome -- if switching to MP4 makes that aspect ratio switch automatic and preserves the superior 720x576 quality as opposed to the 768x576, I'm all for it.

And yes, to get 16:9, I have indeed re-encoded whole videos, but 720x404, not 720x405. It... kind of... made sense to me.

[edDV]

Thanks for a through reply!

1. How does one "rip" analog VHS tapes? Analog PAL tapes have 625 total horizontal lines but only 576 are in the active video frame..

I use Pinnacle PCI-700 card (and Pinnacle Studio 9) for capturing and then re-encode (and cut the commercials) using VirtualDub.

3. Digital broadcast SD video is just like DVD, that is 720x576 but you are capping VHS tapes so ignore that for now.

Let's not ignore it. I have digital broadcast recordings also. My receiver records PVR files which I rename to TS and then convert to AVI (XviD;mp3) using FormatFactory (the only way I know to do it, easy to use for batch converting). Then I use VirtualDub to cut out commercials. I have no idea whether that breaks interlacing or not. I read the wiki article on interlacing, but frankly, I'm still confused what that exactly means -- except that broadcasters like it for technical reasons and it produces the combing effect.

2. If you want to A/D capture 4:3 square pixels, you would purchase a capture card capable of 768x576. Those are uncommon. Most consumer capture cards follow DVD resolution (ITU-Rec601) 720x576 with non-square (rectangular) pixels.

Point is, I don't know what I want. That's essentially what I'm asking here.

4. "AVI" files is unhelpful. AVI is a container spec and has nothing to do with resolution. "Xvid" or "Divx" are codecs that some convert to after 720x576 capture. There are several ways to convert 720x576 to square pixels. The way DVD players or digital TV sets do this is apply a horizontal scale to 768x576 for 4:3 or 1024x768 for 16:9. This preserves interlace. Interlace is fine for DVD or DVB MPeg2. Also AVC or VC1.

So, if I want to watch this file on a television set or a DVD player (I'm assuming you mean standalone player with XviD support, not converting to straight DVD), then I should keep the 720x576, but if I want to view the files on the PC, I should change it to 768x576?

Sorry for the mocking tone toward computer nerds but the worlds of Rec-601 non-square pixels and computer oriented square pixels evolved separately. Other video parameters differ as well

Rec-601 SD video uses Y,Cb,Cr color space, is mostly interlace and is optimized for analog to digital conversion plus efficient use of transmission bandwidth. A key issue is support of both 704x480i 29.97 fps ("NTSC") and 704x576i 25 fps ("PAL") using the same 13.5 MHz sample rate. Rec-601 supports 4:3 or 16:9 aspect ratios by altering pixel aspect ratio. This means all world standards can be handled in a single transmission channel at the same bit rate. Formats derived from Rec-601 include DV, DVD, DVB, ATSC, AVC and VC-1.

Computer square pixel video is generally RGB, progressive, has a more linear gamma and is based on a 4:3 aspect ratio, 640x480 frame at nominal 60Hz display rate. Computer display cards include "full screen" scaling.

The two worlds are bridged by capture hardware, display cards with video overlay buffers and specialized software players. Essentially, analog or digital video must be converted to square pixel, RGB for computer display.

Divx and Xvid commonly use square pixels and have limited support for Rec-601 resolution. In the PAL case, 704x576 is usually deinterlaced, then converted to 704x528 or other multiple of 16 on both axies. Other aspect ratios are accommodated with square pixels such as 2.35 to 1 movies to 720x306 again sized to 16x16 pixel blocks. Often slight side crops or aspect ratio distortions are needed to fit the 16 rule.

These aspect ratios are not strictly legal for DVD without conversion back to 704x576 or 720x576. Divx the company scored a major coup by convincing some DVD player manufacturers to include square pixel divx/xvid codec support with auto scaling into a 720x576 frame. This feature has also been included in many digital TV sets.

So, one can stay in strict Rec-601 resolution and MPeg2 for DVD authoring, or can go rouge with square pixel divx/xvid codecs. All DVD players must play a formal DVD. Results using divx/xvid codecs may vary since this is outside the DVD standard. Screen scaling, levels and gamma may be off when divx/xvid is used. The main quality killers can be artifacts from deinterlace or from over-compression.

[edDV]

5. Unfortunately, your choice of the Xvid codec is both DVD and interlace unfriendly. Xvid is more a hacker computer nerd format.

I've chosen XviD because:
- I have no intention of producing full blown DVDs. I don't find "one movie per disc" size efficient (especially considering the VHS-rip or digital non-HD capture quality) and DVDs are completely unreliable in my experience (I have several Verbatim discs that are unreadable after just a few years).
- XviD is supported by standalone DVD players (should I ever get a better one than I currently have). I have no intention of buying PSP or Xbox.
- XviD is the only codec I've managed to get working properly (though that may be VirtualDub issue -- and I'm considering on moving to Avidemux, especially if MP4 container makes it possible to set aspect ratio flags without re-encoding the whole file).

Computer nerds are interlace phobic and don't even begin to comprehend rectangular pixels. Their reaction to 720x576i capture files is like a little girl seeing a mouse. They cry Eeekkkh! Then they insist on destructive deinterlace, then squish the hulk into square pixels. Some like 720x540 for 4:3 aspect ratio, some like 720x405 for 16:9. But digital video fights back unless resize divides into 16x16 blocks. Fellow geeks laugh at newbies for choosing 720x540 or 720x405.

I did a quick survey and most my videos are 720x576. I didn't notice the aspect ratio difference until recently -- now I do, and I need to set the aspect ratio to 4:3 via VLC interface every time I watch something and it's cumbersome -- if switching to MP4 makes that aspect ratio switch automatic and preserves the superior 720x576 quality as opposed to the 768x576, I'm all for it.

And yes, to get 16:9, I have indeed re-encoded whole videos, but 720x404, not 720x405. It... kind of... made sense to me.

Those are all valid reasons one would choose xvid. One trades some quality by going off standard. Results may be player dependent.

The main alternative to xvid these days is the h.264 codec in various containers. The h.264 codec can be used within strict DVB or Blu-Ray standards or can be used with square pixels like xvid. Players may or may not support all containers or features.

[jagabo]

I did a quick survey and most my videos are 720x576. I didn't notice the aspect ratio difference until recently -- now I do, and I need to set the aspect ratio to 4:3 via VLC interface every time I watch something and it's cumbersome

Run your Xvid AVI files through Mpeg4Modifier and change the aspect ratio flags.

[higgins327]

Run your Xvid AVI files through Mpeg4Modifier and change the aspect ratio flags.

This is excellent! Thank you very much!

Also, many thanks for the technical explanation to edDV!

To summarise:
- I should not re-encode 720x576 to something else
- I should change the aspect ratio flag instead (using Mpeg4Modifier for example)
- Since I can change the AVI aspect ratio flag with Mpeg4Modifier, MP4 container provides no real benefits for me (as that was its main selling point)
- Cropping is the only situation where breaking 720x576 is okay, and even then I should keep the dimensions a multiple of 16

The main alternative to xvid these days is the h.264 codec in various containers. The h.264 codec can be used within strict DVB or Blu-Ray standards or can be used with square pixels like xvid. Players may or may not support all containers or features.

I tried out h.264. The file size is a bit smaller with the same bitrate, but Avidemux gives me only two choices when trying to edit h.264 file -- either the program crashes or I will lose frame accuracy. That's not very promising.

[jagabo]

- Cropping is the only situation where breaking 720x576 is okay, and even then I should keep the dimensions a multiple of 16

Xvid supports as low as mod 2 for progressive material. But it's safer to stick to mod 4 and above (some decoders have problems with mod 2). Efficiency is better at mod 8, best at mod 16.

[lordsmurf]

5. Unfortunately, your choice of the Xvid codec is both DVD and interlace unfriendly. Xvid is more a hacker computer nerd format. Computer nerds are interlace phobic and don't even begin to comprehend rectangular pixels. Their reaction to 720x576i capture files is like a little girl seeing a mouse. They cry Eeekkkh! Then they insist on destructive deinterlace, then squish the hulk into square pixels. Some like 720x540 for 4:3 aspect ratio, some like 720x405 for 16:9. But digital video fights back unless resize divides into 16x16 blocks. Fellow geeks laugh at newbies for choosing 720x540 or 720x405.

I'll stop for questions..

Nice.