[FFmpeg-devel] mpeg12dec fix up DVD caption handling

[Michael Niedermayer]

On Mon, Sep 12, 2016 at 03:28:24PM -0700, Jonathan Campbell wrote:
> These patches fix up the DVD caption handling in mpeg12dec.c to better handle odd cases.
> It's based on code I've written elsewhere to handle captions.
> While it's common for these packets to contain 15 frames worth and start on the odd field there are also DVDs that start on even field or even encode extra fields and switch starting fields.
> Part of the patch is to document comprehensively the format of the DVD caption packet.
> 
> Jonathan Campbell

>  mpeg12dec.c |   27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> a839a0d0e9000ab140f6aef9dee9577f242462bf  0001-add-comments-documenting-the-format-of-the-DVD-CC-us.patch
> From 9213012c7d8ceef2af43fe3c218b1b50728e8f80 Mon Sep 17 00:00:00 2001
> From: Jonathan Campbell <jonathan at castus.tv>
> Date: Mon, 12 Sep 2016 12:34:48 -0700
> Subject: [PATCH 1/2] add comments documenting the format of the DVD CC
>  user-data packet. this is to aid development and maintenance of that code.
> 
> ---
>  libavcodec/mpeg12dec.c | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/mpeg12dec.c b/libavcodec/mpeg12dec.c
> index 204a578..522621a 100644
> --- a/libavcodec/mpeg12dec.c
> +++ b/libavcodec/mpeg12dec.c
> @@ -2262,7 +2262,32 @@ static int mpeg_decode_a53_cc(AVCodecContext *avctx,
>          return 1;
>      } else if (buf_size >= 11 &&
>                 p[0] == 'C' && p[1] == 'C' && p[2] == 0x01 && p[3] == 0xf8) {
> -        /* extract DVD CC data */
> +        /* extract DVD CC data

> +         * for more information see: [https://en.wikipedia.org/wiki/EIA-608#DVD_GOP_User_Data_Insertion]

wikipedia is not a good reference, in fact its not even a
constant reference without a revission. wikipedia can massivly change
and may at times, especially with niche areas be just wrong, the link
itself also wont always work possibly

Please use the specifications itself, H.262 is public, its the 4th
link when searching for H.262 with google for example (wikipedia
refers to H.262 IIUC)

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In fact, the RIAA has been known to suggest that students drop out
of college or go to community college in order to be able to afford
settlements. -- The RIAA
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