[FFmpeg-user] dvdsubs

[Mark Filipak]

On 26/06/2025 13.06, Carl Zwanzig wrote:
> On 6/25/2025 7:01 PM, Mark Filipak wrote:
>> The documentation says that dvdsubs are bit mapped. I don't think so.
> 
> I do think so, as do a lot of other people-
> https://www.loc.gov/preservation/digital/formats//fdd/fdd000571.shtml
> "subtitles are stored as Bitmap images,"

I'm looking at a *.sub in a hex editor. It appears to have been copied, verbatim, from the MPEG2TS. 
I see

                                                     first subtitle
00000000 00 00 01 BA 44 0A 37 F1 C4 01 01 89 C3 F8  pack start & header
0000000E 00 00 01 BD                                private_stream_1 start
00000012 03 D4                                      980 bytes follow
00000014 81 80                                      PES flags
00000016 05                                         extension byte count
00000017 21                                         stream_id
00000018 02 8D FC ...                               payload
000003E8 00 00 01 BE 04 12                          padding start & header
000003EE FF FF FF ...                               padding bytes
00000800                                            next subtitle

All the packets are 2048 bytes (i.e. 0x800).

Looking at the payload, it doesn't look like a bit map, regardless of scope or dimensions. You know 
how regular looking a bit map is in a hex listing, right? A bit map of character shapes, 
line-to-line like a picket fence, is very regular. I've read that the payload is rle, but that was a 
very long time ago. Most of all, it makes sense that it would be rle.

Now, you could very well be correct, Z, and my eyes might be fooling me about the payload, but I'm 
going by what I see, not by the crap on the Internet.

--Mark.