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VOB files are slabs of MPEG-2 program stream lifted straight off a DVD. Convertessa passes them to FFmpeg, which unpicks the multiplex, re-encodes the ageing MPEG-2 picture to H.264 and the AC-3 or LPCM sound to AAC, and writes an MP4 a phone, browser or Apple TV will actually play. Choose a quality value, queue the whole folder, and it all runs locally.
Open a DVD's VIDEO_TS folder and you will find VTS_01_1.VOB, VTS_01_2.VOB, VTS_01_3.VOB and so on. Those are not three features. They are one feature cut into pieces, because the DVD-Video specification caps a single VOB file at one gigabyte. Convert just one of them and you get roughly twenty minutes of film that begins and ends mid-scene. Join them in order first, then convert the joined file:
cat VTS_01_*.VOB > movie.vob
Inside, a VOB is an MPEG-2 program stream: MPEG-2 video, audio as AC-3, DTS, MP2 or uncompressed LPCM, plus subpicture and navigation packets all multiplexed together. FFmpeg pulls that apart, re-encodes the picture to H.264 and the sound to AAC, and writes an MP4. Because MPEG-2 is an old and inefficient codec, a four-gigabyte title routinely lands well under a gigabyte with no visible difference. This is one of the rare conversions where the output shrinks dramatically even at a generous quality value.
IFO files sitting next to the VOBs, not in the VOB itself, so a conversion that reads only the VOB has no way to know where they were.Two more things worth knowing before you judge the result. DVD video uses non-square pixels, 720 by 480 for NTSC and 720 by 576 for PAL, with a flag stating whether to display the picture as 4:3 or 16:9; that flag travels into the MP4, so a player that honours it shows the right shape and one that ignores it shows a squashed one. And most discs are interlaced, stored as two fields per frame, which is why motion can comb on a progressive screen. Neither effect is introduced by the conversion. Both were pressed onto the disc.
A DVD title is cut at one-gigabyte boundaries. In Terminal, run cat VTS_01_*.VOB > movie.vob inside the VIDEO_TS folder so the feature converts as one film rather than twenty-minute fragments.
Add the joined file to the queue and choose MP4. FFmpeg demultiplexes the program stream, re-encodes MPEG-2 video to H.264 and the AC-3 or LPCM audio to AAC in the same pass.
MPEG-2 wastes a great deal of space, so even a generous quality value usually yields a file a quarter of the disc's size. Expect a feature-length title to take several minutes to finish.
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Because you converted one fragment. The DVD-Video spec limits each VOB to one gigabyte, so a feature is split across VTS_01_1.VOB, VTS_01_2.VOB and however many more it needs. Join them in numerical order before converting:
cat VTS_01_*.VOB > movie.vob && convertessa movie.vob --to mp4 --quality 85 -o ~/Movies
The shell expands the wildcard in sorted order, which is exactly the play order on the disc.
They were never text. DVD subtitles are a subpicture stream of compressed bitmap images overlaid on the video, one small picture per subtitle. MP4's subtitle tracks store characters, so there is no way to carry a bitmap subtitle across as a subtitle. If you need them, the usual route is a separate tool that reads the subpicture stream and produces a subtitle file you can pair with the MP4 yourself.
Only if they are readable as ordinary files. Most retail discs are scrambled with CSS, so the VOBs copied off them are encrypted and decode to noise. Convertessa converts files that already sit readable on your disk and does not decrypt anything. Home-burned discs, camcorder DVDs, corporate and training discs and anything authored without copy protection are unencrypted and convert directly.
DVD stores non-square pixels. A widescreen NTSC feature is 720 by 480 samples on the disc with a flag saying to display it at 16:9, and a 4:3 title uses the same sample count with a different flag. That flag is carried into the MP4, but a player or web component that ignores it will draw the raw sample grid and everyone will look too tall or too wide. Try the file in a second player before assuming the conversion went wrong.
Interlacing. Standard-definition DVD holds two fields per frame captured a fiftieth or sixtieth of a second apart, which a tube television drew alternately and never showed as a whole frame. On a progressive display, horizontal motion tears into a comb pattern. The disc was authored that way, so it is present in the source rather than introduced by the conversion. Film-sourced discs suffer less than material shot on video.
The one the demultiplexer maps by default, which is normally the first audio stream in the program stream and usually the disc's primary language. A director's commentary or a second dub sitting later in the multiplex is not guaranteed to be carried across. Play the first minute of your converted file before running the rest of the disc, and if the wrong track came out, check whether the title has a separate VOB set for that language.
Yes, and it is the right move when a disc holds several separate titles, such as an episode collection:
convertessa ~/Rips/VIDEO_TS/*.VOB --to mp4 --quality 85 -o ~/Movies
Be aware of what that produces: one MP4 per VOB file, which means one MP4 per fragment. For a single feature split across four VOBs, join them first. For a disc where each VOB really is a separate short, the batch is exactly what you want.
Far smaller than the disc. A dual-layer DVD holds up to 8.5 GB and a single-layer one 4.7 GB, nearly all of it spent on MPEG-2 video that H.264 encodes far more efficiently. A feature film typically lands between 700 MB and 1.5 GB at a generous quality value, and looks the same on any modern screen. Standard definition simply does not need much space once a modern codec is doing the work.