On Mon, Jan 27, 2025 at 7:03 PM Soft Works <softwo...@hotmail.com> wrote: > > > From: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> On Behalf Of > > Kieran Kunhya via ffmpeg-devel > > Sent: Monday, January 27, 2025 10:40 AM > > > While this is a very valid concern for some kinds of frame side > > data, it > > > does not apply to CC data. It's either in every frame or none. If a > > > provider generally broadcasts CC, then it's always present in every > > frame, > > > even during programs for which no CC is available - it's always > > there. Like > > > I mentioned at the top, we're using the properties field from the > > codec > > > (via codec_par) and there hasn’t been a single case reported where > > the CC > > > detection this way would have been incorrect. > > > > > > > This isn't true, CC data is sparse. > > I have no opinions about the rest of the text. > > > > Kieran > > Hi Kieran, > > I found it 😊 > > It's in EIA-708-A from 1999 as well as in the latest successor spec > ANSI/CTA-708-E S-2023 > > from chapter 4.1 (1999): > > "for DTV and DTVCC specific (Le., ATSC A/53) caption encoding, the DTV > Closed-Captioning channel is a continuous 9600 bps stream allocated from the > DTV signal capacity" > (the latest version adds more variations) > > and chapter 4.2 (1999): "Pre-Allocated Bandwidth" > > "The DTVCC Transport Channel is a fixed, pre-allocated stream which exists in > all DTV-system bit streams, even though captions may not be present. This > ever-present bandwidth (which includes NTSC and DTVCC caption data) allows > encoders to easily insert caption data into the DTV bit-stream at the point > of origin and at multiple down-stream encoding points without having to > perform complex picture data processing and bandwidth reallocation"
Not everyone follows this. Kieran _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
