Although they have similar bitrates, HD streaming is vastly superior to SD DVD except a slight advantage in audio to DVD. There are many reasons for this.
- SD DVD format was developed in the early 90s to work with analog tube TVs which made up 99% of the TVs at the time.
- The dominant TV format at the time was NTSC for the US and PAL for Europe. DVD format had to closely mimic their specs for full comparability of all displays.
- NTSC format is 480 vertical lines of resolution but in reality only half of them could be visible at a time due to ‘about’ 7 MHz analog bandwidth on the broadcast. (VHS tapes had half this bandwidth hence the recorded tapes looked worse than the original broadcast).
- NTSC format used interlacing to split the 480 line images which is showing the odd lines first then the even lines. They called these half frames ’fields’. Hence where the name 480 interlaced or 480i comes from.
- So in essence it is 60 fields per second as the refresh rate, not 60 frame as commonly known. When odd and even lines are combined, it is 30 frames per second.
-There is a fundamental problem with this frame number. Films are shot in 24 frames and there isn’t an integer to multiply it with to convert it to 30 frames (or 60 frames). They had to develop a telecine method called 2:3 pulldown (again 3:2 pulldown is incorrectly used in most places) which means the first frame is repeated twice and the second frame is repeated 3 times and so on. This way 24 frames could be converted to 30 frames.
-Modern displays can display full 480 lines at once without an issue. They can combine the odd and even fields to reconstruct the original 480 line frames. This process is known as de-interlacing or progressing scan. Reconstructed 480 line frames are also called 480 progressive or 480p.
-They use the inverse of 2:3 pulldown which is called 2:3 pull up to reconstruct the original 24 frames as well.
-For PAL in Europe, the resolution is 576 vertical lines and the refresh rate is 50 fields (or 25 frames). Interlacing works the same way as NTSC. To convert 24 frame films to 25 frames, the film is sped up by 4%. This causes a slight pitch in audio and corrected with EQ in mastering. Some poorly authored PAL DVDs will miss this and have distorted audio.
-The telecine method 2:3 pull down and interlacing works fine for the most part. The inverse operation can reconstruct original frame resolutions and rates in ideal situation as well. However, there are many cuts and edits that make up a complete movie. The DVD mastering engineer must pay extreme attention to cadence breaks where edits and cuts are made in the movie.
-A cadence break (end or begin) might not always occur right after the last 24th frame of that scene. For example if the cut/edit is a 20.3 second scene, there are only 7 frames at the end (the last 0.3 seconds). When reversing this telecine, the display may ‘incorrectly’ do a 2:3 to pull up on that 7 frames (fractional second) which will result jitter in the image.
-Continuing the above example, the de-interlacing algorithm expect an equal number of even and odd fields from that scene. If the fractional second isn’t carefully handled in mastering, it may result in 1 extra even or odd fields than there should be. This extra field doesn’t have it’s matching field to combine to a full frame. The de-interlacer may ‘incorrectly’ combine it with the first field from the next scene and result in a mismatched image.
-These were only a handful of scenarios things can go wrong but there are many more. In short, combining interlaced fields to form progressive frames and reconstructing the native 24 frame per second rate is a complicated process and often has many de-interlacing and 2:3 pull up artifacts.
-DVDs are digital but they match the above mentioned (analog) NTSC specifications for compatibility with analog tube TVs. Digital processing at the time wasn’t great either. The digital decoders in the early DVD players couldn’t handle 480 progressive images anyway. Hence all these compromises were necessities in a way.
-DVDs are encoded in Mpeg-2 compression which is not very efficient by today’s standards. DVD format allows up to 10 mbps bandwidth but 5 to 7mbps average bitrates are a lot more common. Some poorly authored discs will have less than 4 mbps average bitrates because they want to fit longer runtimes on a single disc. A single layer DVD could hold 4.7GB and a dual layer is 8.5GB. At close to 10 mbps bitrates a dual layer DVD can hold about 2 hours of video. Some early DVD releases with longer than 2 hour run times such as Dances with Wolves were split onto 2 discs to keep bitrates high but later re-releases compressed it (half the bitrates) to fit the entire film onto a single disc.
-Also keep in mind the extras and many audio tracks will steal away room precious space reducing available size to video. Sony released some movies under “Superbit DVD” in the late 90s and the early 00s. These had zero extras on the disc and utilized the entire dual layer for the video and a single audio track (typically DTS). Some of these releases came with a second separate disc for the extras.
-So far I only mentioned the technical limitations. Another major issue with SD DVDs were where the masters came from. Often times, studios used the same masters made for the NTSC broadcast or the VHS release (for home video). These masters were not optimized for digital compression hence they produced digital artifacts such as banding, mosquito noise (pixelation around objects), block noise (mpeg compression blocks don’t merge in correctly). Later DVD re-releases addressed this issue. You will see digitally remastered on some DVD releases.
-In the audio department, DVD format supported 2ch PCM in up to 24 bit/ 96 KHz but this was rarely used except some music/concert releases. Nearly all movies had Dolby Surround AC-3 (Advance Codec 3rd generation) audio soundtracks, later renamed to be Dolby Digital. Dolby Digital supported up to 5.1 channels of discreet audio in 16 bits/48KHz. The bitrate can be up to 640kbps but I am not aware of any DVD to have this. Nearly all DVDs had Dolby Digital 5.1 in 448kbps or Dolby Digital 2.0 in 192kbps. There are some very few odd releases with Dolby Digital 4.0 (3 fronts and a single mono rear) And Dolby Digital 3.0 (Stereo fronts and a single mono rear). These bitrates may seem very little compared to Dolby TrueHD and DTS HD-MA but professional movie theater had Dolby Stereo AC-3 in only 320kbps on 35mm film reels. Dolby Stereo name was used for the professional cinemas where as Dolby Surround name for home video. Essentially they are the same thing except the bitrates. Later they were both renamed to be Dolby Digital.
-For Star Wars Episode 1 The Phantom Menace, Dolby developed a new format called Dolby Digital EX which has 5.1 discreet channels but the rear channels included an additional audio channel matrixed in. The Dolby Digital EX decoder can unfold this channel for 6.1 (3 fronts, 2 discreet rears and a single matrixed rear center). There were a handful other releases in this format later.
-DVD format had a minor revision into its second year and included DTS as an optional soundtrack. DTS was also up to 5.1 channels and a lossy format like Dolby Digital but supported up to 1.5mbps bitrates. There is about 30 films encoded with full 1.5mbps bitrate DTS but all other releases used a reduced rate encoding at 755kbps. This is still a marked improvement compared to Dolby Digital at 448kbps.
-DTS soundtracks in professional movie theaters were printed on red-book CDs and played in sync with the 35mm film. Because of this they had the red-book standard 1.4mbps bitrate. They also had to reduce the 48KHz sampling rate to 44.1kHz.
-DTS followed up with DTS EX right after Dolby Digital EX. It also has a matrixed in rear mono center.
-DTS later released another revision and called it DTS ES which has 6.1 discreet channels. Unfortunately, all DTS ES encoded DVDs were in 755kbps bitrate. All full 1.5mbps full bitrate DTS DVDs were 5.1 only.
-Ok, now let’s talk about streaming. For some reason SD streaming (and Kaleidescape downloads) are also loyal to the specifications adopted for the SD DVD which were derived from the analog NTSC format. So the SD streaming also has the interlacing and telecine issues.
-Streaming platforms adopted mpeg-4 and other more efficient compression algorithms to reduce their bandwidth. For example, mpeg-4 is up to 4 times more efficient than mpeg-2 compression. So the streaming version could be at 3 or 4 mbps and still look better than the SD DVD with 7 mbps bitrate.
-Streaming in HD is almost always in progressive and the native 24 frame rate hence immune from deinterlacing and reverse telecine artifacts. This alone makes HD streaming a marked improvement over SD DVDs.
-HD streaming bitrates can be much higher, sometimes well above 10 mbps on average. With the much higher efficiency codecs, this results in much clearer picture and a lot less digital artifacts compared to SD DVD and SD streaming.
-Streaming services cut the most corners on audio soundtracks. They use a later revision of Dolby Digital, called Dolby Digital Plus with much lower bitrates but higher number of discreet speaker channels. Dolby Digital Plus is often in 220kbps range for streaming and can have 7.1 channels. Dolby Atmos can be folded in (metadata) in Dolby Digital Plus so the channel count can be much higher but the bitrates are still under 400kbps. Dolby claims Dolby Digital Plus compression is higher efficiency than Dolby Digital. They also claim Dolby Digital Plus with 220kbps will surpass Dolby Digital with 448kbps but my ears disagree with this.
-I know it’s a long read but this is nearly the entire story and it should make it clear why SD video should be avoided unless it is the only option.
Too long, didn’t want to read version of the above in a short summary is, HD streaming is vastly superior in video but DVDs with full bitrate DTS soundtracks will blow any streaming (including 4K streaming) out of the water. In most cases reduced bitrate DTS DVDs will sound better than any streaming. Dolby Digital DVDs will sound better than SD and HD streaming in general.
There is another non-audio video related benefit of SD DVD which is availability of different version which are unavailable in HD . Some films released on DVD had different cuts, different extras and different commentary tracks. In some cases HD and 4K releases were not approved for director’s cuts, special editions, special TV cuts. The rights change hands and the new label doesn’t own the commentary tracks or the special extras. For instance Scream (1996) was released unrated from Dimension Films. Dimension Films were later acquired by Disney which doesn’t do unrated films. Some scenes were cut to make the film rated R. So if you want the unrated Director’s Cut of the film, you need to hunt down the VHS, Laserdisc or early DVD release of this film from Dimension Films before Disney acquisition. Ironically there are more such examples for VHS and Laserdiscs releases predating DVDs because home video licensing was not as complicated as now. For instance, if you want to watch Star Wars the original trilogy in their theatrical versions without any CGI and enhancements added in the later DVD, Blu-ray and 4K releases, you need the VHS and Laserdiscs prior to 1993. CBS/Fox handled these releases and put out home video releases in VHS and Laserdisc which are nearly identical to what people saw in theaters back in 1977 to 1983. George Lucas later changed over 100 scenes from each film and released his ’Special Editions’ in 1997. He later made a ton of more changes and released them again in 2011 on Blu-rays then made even more changes in 2020 for the 4K UHD Blu-rays. Fans have been asking for the unaltered versions on home video for decades but Lucas and Disney have been ignoring them. You can see some of the changes in the YouTube video link below.
Star Wars 1977 vs 2011 versions
