[FFmpeg-devel] [PATCH] libx264: copy A53 closed captions from source

[Anshul]

On 09/26/2015 05:46 AM, DeHackEd wrote:
> Assumes 'GA94' format (ATSC standard)
>
> Signed-off-by: DHE <git at dehacked.net>
> ---
>   doc/encoders.texi    |  5 +++++
>   libavcodec/libx264.c | 37 +++++++++++++++++++++++++++++++++++++
>   2 files changed, 42 insertions(+)
>
> diff --git a/doc/encoders.texi b/doc/encoders.texi
> index 3550bcc..bb16dea 100644
> --- a/doc/encoders.texi
> +++ b/doc/encoders.texi
> @@ -2069,6 +2069,11 @@ For example to specify libx264 encoding options with @command{ffmpeg}:
>   ffmpeg -i foo.mpg -vcodec libx264 -x264opts keyint=123:min-keyint=20 -an out.mkv
>   @end example
>
> + at item a53cc
> +Import closed captions (which must be ATSC compatible format) into output.
> +Only the mpeg2 and h264 decoders provide these. Default is 0 (off).
> +
> +
>   @item x264-params (N.A.)
>   Override the x264 configuration using a :-separated list of key=value
>   parameters.
> diff --git a/libavcodec/libx264.c b/libavcodec/libx264.c
> index 58fcfb0..4227bcc 100644
> --- a/libavcodec/libx264.c
> +++ b/libavcodec/libx264.c
> @@ -83,6 +83,7 @@ typedef struct X264Context {
>       int avcintra_class;
>       int motion_est;
>       int forced_idr;
> +    int a53_cc;
>       char *x264_params;
>   } X264Context;
>
> @@ -256,6 +257,7 @@ static int X264_frame(AVCodecContext *ctx, AVPacket *pkt, const AVFrame *frame,
>       int nnal, i, ret;
>       x264_picture_t pic_out = {0};
>       int pict_type;
> +    AVFrameSideData *side_data;
>
>       x264_picture_init( &x4->pic );
>       x4->pic.img.i_csp   = x4->params.i_csp;
> @@ -278,6 +280,40 @@ static int X264_frame(AVCodecContext *ctx, AVPacket *pkt, const AVFrame *frame,
>                                               X264_TYPE_AUTO;
>
>           reconfig_encoder(ctx, frame);
> +
> +        if (x4->a53_cc) {
> +            side_data = av_frame_get_side_data(frame, AV_FRAME_DATA_A53_CC);
> +            if (side_data) {
> +                x4->pic.extra_sei.num_payloads = 1;
> +                x4->pic.extra_sei.payloads = av_mallocz(sizeof(x4->pic.extra_sei.payloads[0]));
> +                x4->pic.extra_sei.sei_free = av_free;
> +
> +                x4->pic.extra_sei.payloads[0].payload_size = side_data->size + 11;
> +                x4->pic.extra_sei.payloads[0].payload = av_mallocz(x4->pic.extra_sei.payloads[0].payload_size);
> +                x4->pic.extra_sei.payloads[0].payload_type = 4;
> +                memcpy(x4->pic.extra_sei.payloads[0].payload + 10, side_data->data, side_data->size);
> +                x4->pic.extra_sei.payloads[0].payload[0] = 181;
> +                x4->pic.extra_sei.payloads[0].payload[1] = 0;
> +                x4->pic.extra_sei.payloads[0].payload[2] = 49;
> +
> +                /**
> +                 * 'GA94' is standard in North America for ATSC, but hard coding
> +                 * this style may not be the right thing to do -- other formats
> +                 * do exist. This information is not available in the side_data
> +                 * so we are going with this right now.
> +                 */
I think GA94 is correct for this situation, since in our x264 decoder we 
don't consider any other standard
for extracting closed caption.

I don't know if we have any logic which differentiate between ATSC, ISDB 
or DVB we parse all transport stream
in same manner. if someone know where we differentiate atsc and dvb in 
FFmpeg please point me there.

Note: This logic will also fail when x264 is muxed in formats like gxf 
where closed caption are kept in vbi instead
of GA94.

Overall  LGTM.

I don't know how to apply encrypted mails using git, and when I save 
your email in Thunderbird, git am is unable to apply.
if you can send the same patch as attachment or command to convert 
encrypted .eml file to normal patch I would test this too.

-Anshul