Category Archives: digital video

Comparing BitTorrent Downloads of Interlaced TV Shows

In my previous blog post, I was comparing how internet video providers like Hulu, Netflix, iTunes, Amazon and Zune handle interlaced material by comparing an episode of Futurama. This time, let’s see how rips from the BitTorrent network compare to these.

I managed to acquire nine different files (I own several licenses for this episode, and I downloaded without uploading). Some of these have non-english audio tracks and some have hard subtitles, but let’s concentrate on the quality of the deinterlacing. The following list is already sorted by overall quality, first by interlacing quality, then by resolution, then by data rate:

# Filename Mbit/sec Encoder Cropping Resolution fps Deinterlacing
1 Futurama – 09 – Hell Is Other Robots.avi (184287232 bytes) 1.1 MPEG-4 yes 384×288 25 lots of blending
2 Futurama – S01E09 – Hell Is Other Robots.avi (175728640 bytes) 1.1 MSMPEG4 yes 576×432 24.03 lots of blending
3 Futurama – 1×09 – El infierno está en los demás robots.avi (181534720 bytes) 1.1 MPEG-4 yes 640×480 25 lots of blending
4 Futurama 1.09 – el infierno robot – xvid -español latino.avi (183535616 bytes) 1.1 MPEG-4 yes 640×480 23.98 detelecine, blend
5 Futurama – 1×09 – Hell Is Other Robots.mp4 (83770003 bytes) 0.5 MPEG-4 yes 320×480 29.97 detelecine with 30fps dups
6 Futurama – S01E09 – Hell Is Other Robots.m4v (77853226 bytes) 0.5 H.264 yes 480×368 24.97 detelecine
7 Futurama.S01E09. SWESUB.DVDRip.XviD-Enectrixx.avi (183445504 bytes) 1.1 MPEG-4 no 544×384 25 detelecine
8 S01E09 – Hell Is Other Robots.avi (183490560 bytes) 1.1 MPEG-4 yes 640×480 25 detelecine
9 Futurama – S01E09 – Hell Is Other Robots [dd].avi (183492608 bytes) 1.1 MPEG-4 yes 640×480 25 detelecine

Files #1, #2 and #3 show heavy blending that goes beyond just blending the two interlaced frames per five frames. It is likely these files were encoded form a PAL source that was improperly converted from NTSC.

File #4 is detelecined (24 fps), but whenever the telecine pattern was not consistently PPPII (“Robot Hell” pan, end credits), the algorithm reverted to blending the two fields. It is likely this source was encoded from the NTSC DVD.

Files #6, #7, #8 and #9 all seem to be encoded from the same PAL source that was already deinterlaced properly, i.e. a detelecine was done to recover the 24 fps video, and then it was sped up by ~4% to get a 25 fps video. The detelecine is almost perfect: In the end credits, the algorithm properly reconstructed all frames without ever having to blend, but the “Robot Hell” pan is missing the six frames that that only existed as one field.

File #5 is interesting: It is 30 fps, so it has a duplicate frame after every fifth frame, but other than that, it was converted by the same high-quality detelecine as #6 through #9. Since I suspect that the #6-#9 detelecine was done professionally for the PAL DVD, it is weird to see the practically the same result (6 missing frames in “Robot Hell”, but perfect end credits etc.) with the NTSC frame rate here. It almost looks like someone took a PAL DVD (or one of the files #6-#9) and duplicated frames to get an NTSC-compatible signal.

Bittorent Summary

A rule of thumb is that an encoding found on BitTorrent is as good as its source. For those that had a blended source (#1-#3), nothing could fix it. For those that had an excellent progressive source (#6-#9), there was little to be done wrong. The one that had the original interlaced US master as a source did an okay job of deinterlacing.

Also: The PAL DVDs seem to be very high quality.

Comparison to properly licensed sources

Now how do these scene rips compare to legit internet video providers? Well, as my previous article stated, the files on Hulu, Netflix and iTunes have the deinterlacing done wrong, leading to visible and unnecessary degradations of the vertical resolution in some (Netflix, iTunes) or all (Hulu) of the video – but this is arguably still better than the blending of BitTorrent files #1-3. Amazon Video on Demand did an okay detelecine job, although inferior to BitTorrent file #4: On complicated scenes, Amazon halved the resolution, while file #4 did blending. The Microsoft Zune store did a perfect detelecine, which is even better than the one in BitTorrent files #4-9, since it did not miss the 6 frames in the “Robot Hell” pan, but otherwise performs as well as the PAL DVD.

So here are the final rankings of the different sources/files/enodings for the episode “Hell Is Other Robots” of Futurama:

0. NTSC DVD: original broadcast master, 720×480, interlaced, but with the full potential to be perfectly deinterlaced! ;-)

1. Microsoft Zune: perfect detelecine
2. PAL DVD: almost perfect detelecine
3. BitTorrent files #6-#9: almost perfect detelecine, like PAL DVD
4. BitTorrent file #4: okay detelecine
5. Amazon Video on Demand: okay detelecine, judder
6. iTunes, Netflix: buggy deinterlacing, judder
7. BitTorrent files #1-3: horrible blending
8. Hulu: Consistenly halved vertical resolution

So unless you want to do the deinterlacing yourself, the Zune version is the best choice. Which is, unless you actually want to play the video on the devices you care about, in which case you should get the effectively not copy-protected PAL DVDs.

Comparing Digital Video Downloads of Interlaced TV Shows

In the days of CRT monitors, TV shows used to be broadcast in interlaced mode, which is unsupported by modern flat-panel displays. All online streaming services and video stores provide progressive video, so they must deinterlace the data first. This article compares the deinterlacing strategies of Apple iTunes, Netflix, Microsoft Zune, Amazon VoD and Hulu by comparing their respective encodings of a Futurama episode.

If you have dealt with video formats before, you probably know about interlacing, a 1930s trick to achieve both high spatial and temporal resolution at half the (analog) data rate: In NTSC countries, there are 60 fields per second (PAL: 50), and every field is half the vertical resolution of a full frame. When film footage at 24 frames per second has to be played at 30 fps (NTSC), every frame has to be shown 1.25 times – in other words, every fourth frame has to be shown twice. This introduces jerky motion (judder), but it can be improved by using the 60 Hz temporal resolution: Frame A gets shown for 2 fields, frame B for 3 fields, frame C for 2 fields, and so on. This way, every source frame gets shown for 2.5 fields, i.e. 1.25 frames – this method is called a telecine 2:3 pulldown.

A lot of TV material is produced at 24 fps and telecined, for several reasons: Standard movie cameras can be used instead of TV cameras, 24 fps can be converted to 25 fps PAL more easily than 30 fps NTSC, and for cartoons, this means that only 24 (or 12) frames have to be drawn for every second.

Unfortunately, interlacing only works with ancient CRT TVs – modern LCD screens can only show progressive video. And while DVDs are specified to encode interlaced video, more modern formats like MPEG-4/H.264 and VC-1 usually carry progressive data. So when playing DVDs, the DVD player or the TV have to deal with the interlacing problem, and in case of modern file formats, it’s the job of the converter/encoder.

The naive way of converting an interlaced source to progressive is to combine every two fields into a frame. This works great if the original source material was 30 fps progressive (which is rare for NTSC but common for PAL), but for telecined video, since two out of every six frames are combined from two different fields, this leads to ugly combing effects.

If the source material was 24 fps, an inverse telecine can be done, recovering the original 24 frames per second. Unfortunately, it is not always this easy, since interlaced video may switch between methods, and sometimes use different methods at the same time, e.g. overlaying 30 fps interlaced captions on top of a 24 fps telecined picture, or compositing two telecined streams with a different phase. “Star Trek: The Next Generation” is a famous offender in this category – just single-step through the title…

In the following paragraphs, let us look at an episode of Futurama and how the deinterlacing was done by the different providers of the show. Futurama was produced in 24 fps and telecined. Some of the editing seems to have been done on the resulting interlaced video, so the telecine pattern is not 100% consistent.

NTSC DVD

The NTSC DVD is basically just an MPEG-2-compressed version of the US CCIR 601 broadcast master. It encodes 720×480 anamorphic pixels (which can be displayed as 640×480 or 720×540) and has all the original interlacing intact. This is a frame at 640×480 and properly inverse telecined:

DVD

Hulu

Hulu

Hulu (480p version) took the original image without doing any cropping on the sides. You can clearly see this picture is only half the vertical resolution, meaning one of the fields got discarded. It seems this was Hulu’s deinterlacing strategy, since throughout the complete video, everything is half the vertical resolution, whether there is motion or not. This also keeps the video at 30 fps, and effectively shows every fourth frame twice, introducing stronger judder.

iTunes

iTunes

iTunes crops the picture to get rid of the black pixels in the overscan area and scales it to 640×480. They run a full-blown 60 Hz deinterlace filter on the video. Such a filter is meant to take a live television signal as an input, with a temporal resolution of 60 Hz. While this looks fine on frames with no or little motion, vertical resolution is halved as soon as there is motion. Basically, it is the wrong filter. Like Hulu, iTunes preserves the 30 fps, introducing a stronger judder. (The video encoding is H.264 at 1500 kbit/sec.)

Netflix

Netflix

Netflix seems to do the same as iTunes – maybe they even got the data from iTunes? The image is cropped and scaled to 640×480, they run a deinterlace-filter and retain the 30 fps, leading to halved resolution when there is motion, and stronger judder.

Amazon Video on Demand

Amazon Video on Demand

Amazon Video on Demand with its horribly inconvenient Unbox Player (Windows only, requires 1 GB of extra downloads and two reboots) did a better job. Like Netflix and iTunes, they cropped the picture and scaled it to 640×480, but they actually did a real inverse telecine. In some segments (like the end credits), the algorithm failed because of inconsistencies of the original telecine, so it reverted to half the vertical resolution. And like the others, Amazon also encodes at 30 fps, i.e. judder. (The video encoding is VC-1 at 2600 kbit/sec.)

Zune

Zune

Microsoft’s Zune Store provides a cropped video at 640×480 at the original 24 fps and with a bitrate of 1500 kbit/sec (VC-1). Looking through it frame by frame reveals that they used a brilliant detelecine/deinterlace algorithm. On the DVD, the panning at the beginning of the “Robot Hell” song is very tricky: It breaks the standard telecine pattern (PPPIIPPPII becomes PPPIPPPI), it seems every fifth frame was removed.




The pan consists of a pattern of three progressive frames, and then one interlaced frame, which is composed of the previous frame and the current frame. Consequently, every fourth frame has half its resolution wasted by the repeated lines of the previous frame, i.e. every fourth frame only exists at half resolution in the DVD master material.

Hulu discards half the vertical resolution for every frame anyway, and the deinterlacing algorithms of iTunes and Netflix discard half the resolution whenever there is motion. The Amazon algorithm does a good job when the telecine pattern is correct, but in this case, it gets confused and encodes all frames of the pan in half resolution. The Zune algorithm does a brilliant job here: The progressive frames stay at full resolution, and it extracts the half-resolution picture out of every fourth frame:




This is the fourth picture at full size – you can see half the vertical resolution is missing (it was never there in the first place!), but the algorithm did a very good interpolation job:

Robot Hell (Zune)

The Zune video is almost perfect. It recombines all fields correctly and recovers all single fields, scaling them up so that it’s hardly visible there is information missing. If you ignore the 720 vs. 640 horizontal pixels, the resulting 24 fps video contains all information of the DVD version, but with all interlacing removed, and with zero judder. Too bad it’s not H.264, but DRMed and only plays on Windows (XP+), Zune and Windows Phone 7.

Summary

Provider Cropping Resolution Deinterlacing fps Encoder Bitrate (kbits/sec)
NTSC DVD no 720×480 none 30 MPEG-2 6500
Hulu no 640×480 discard 30 H.264? ?
iTunes yes 640×480 30 Hz deinterlace 30 H.264 1500
Netflix yes 640×480 30 Hz deinterlace 30 H.264/VC-1 ?
Amazon VoD yes 640×480 detelecine+decomb 30 VC-1 2600
Zune yes 640×480 fuzzy detelecine 24 VC-1 1500

Note: H.264 and VC-1 compress significantly better than MPEG-2; a rule of thumb is to divide the MPEG-2 bitrate by 2.3 to get a comparable H.264/VC-1 bitrate. So the Amazon bitrate is fine and the video is about the same quality (sharp picture, no compression artefacts) as the DVD, but the iTunes and Zune versions are not (artifacts can be seen on single frames).

It is scary how little effort seems to be going into video conversion/encoding at major players like iTunes, Netflix and Hulu. Amazon did a kind of okay job converting the source material properly, and only Microsoft did an excellent job. The NTSC DVDs still give you the maximum quality – but of course, if you watch them on an LCD, the burden of deinterlacing is on your side. Handbrake with “detelecine” (for the bulk of it) and “decomb” (for exceptions) turned on, and with a target framerate of “same as source” will generate a rather good MP4 video similar to Amazon’s, but without the judder.

Are there any stores I missed? Can someone check the PAL DVD as well as digital PAL and NTSC broadcasts? What is the magical detelecine/deinterlace program Microsoft uses?

See also: Comparing Bittorrent Files of Interlaced TV Shows