[FFmpeg-devel] [PATCH] movtextdec: 3GPP TS 26.245 Timed Text Decoder.

Nicolas George nicolas.george at normalesup.org
Sun Jul 8 17:13:34 CEST 2012


L'octidi 18 messidor, an CCXX, Philip Langdale a écrit :
> This change introduces a basic decoder for 3GPP Timed Text subtitles,
> also known as TX3G, Quicktime subtitles, or "movtext" in the existing
> code.
> 
> This initial change doesn't attempt to parse styling information,
> and just reads the plain text of the subtitles. I intend to add
> support for styles eventually, but it's challenging due to a lack
> of existing players that support them.
> 
> Signed-off-by: Philip Langdale <philipl at overt.org>
> ---
>  Changelog                  |    1 +
>  doc/general.texi           |   21 ++++-----
>  libavcodec/Makefile        |    1 +
>  libavcodec/allcodecs.c     |    1 +
>  libavcodec/movtextdec.c    |  106 ++++++++++++++++++++++++++++++++++++++++++++
>  libavcodec/version.h       |    2 +-
>  tests/fate/subtitles.mak   |    3 ++
>  tests/ref/fate/sub-movtext |    1 +
>  8 files changed, 125 insertions(+), 11 deletions(-)
>  create mode 100644 libavcodec/movtextdec.c
>  create mode 100644 tests/ref/fate/sub-movtext
> 
> diff --git a/Changelog b/Changelog
> index b5db610..43a39bb 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -21,6 +21,7 @@ version next:
>  - RealText demuxer and decoder
>  - Heart Of Darkness PAF playback support
>  - iec61883 device
> +- 3GPP Timed Text decoder
>  
>  
>  version 0.11:
> diff --git a/doc/general.texi b/doc/general.texi
> index d1925c0..733ea95 100644
> --- a/doc/general.texi
> +++ b/doc/general.texi
> @@ -864,16 +864,17 @@ performance on systems without hardware floating point support).
>  
>  @multitable @columnfractions .4 .1 .1 .1 .1
>  @item Name @tab Muxing @tab Demuxing @tab Encoding @tab Decoding
> - at item SSA/ASS      @tab X @tab X @tab X @tab X
> - at item DVB          @tab X @tab X @tab X @tab X
> - at item DVD          @tab X @tab X @tab X @tab X
> - at item JACOsub      @tab X @tab X @tab   @tab X
> - at item MicroDVD     @tab X @tab X @tab   @tab X
> - at item PGS          @tab   @tab   @tab   @tab X
> - at item RealText     @tab   @tab X @tab   @tab X
> - at item SAMI         @tab   @tab X @tab   @tab X
> - at item SubRip (SRT) @tab X @tab X @tab X @tab X
> - at item XSUB         @tab   @tab   @tab X @tab X
> + at item SSA/ASS          @tab X @tab X @tab X @tab X
> + at item DVB              @tab X @tab X @tab X @tab X
> + at item DVD              @tab X @tab X @tab X @tab X
> + at item JACOsub          @tab X @tab X @tab   @tab X
> + at item MicroDVD         @tab X @tab X @tab   @tab X
> + at item PGS              @tab   @tab   @tab   @tab X
> + at item RealText         @tab   @tab X @tab   @tab X
> + at item SAMI             @tab   @tab X @tab   @tab X
> + at item SubRip (SRT)     @tab X @tab X @tab X @tab X
> + at item 3GPP Timed Text  @tab   @tab   @tab   @tab X
> + at item XSUB             @tab   @tab   @tab X @tab X
>  @end multitable
>  
>  @code{X} means that the feature is supported.
> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> index d50a40e..2b18234 100644
> --- a/libavcodec/Makefile
> +++ b/libavcodec/Makefile
> @@ -265,6 +265,7 @@ OBJS-$(CONFIG_MJPEGB_DECODER)          += mjpegbdec.o mjpegdec.o mjpeg.o
>  OBJS-$(CONFIG_MLP_DECODER)             += mlpdec.o mlpdsp.o
>  OBJS-$(CONFIG_MMVIDEO_DECODER)         += mmvideo.o
>  OBJS-$(CONFIG_MOTIONPIXELS_DECODER)    += motionpixels.o
> +OBJS-$(CONFIG_MOVTEXT_DECODER)         += movtextdec.o ass.o
>  OBJS-$(CONFIG_MP1_DECODER)             += mpegaudiodec.o mpegaudiodecheader.o \
>                                            mpegaudio.o mpegaudiodata.o
>  OBJS-$(CONFIG_MP1FLOAT_DECODER)        += mpegaudiodec_float.o mpegaudiodecheader.o \
> diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
> index ef75b08..7ac4eb0 100644
> --- a/libavcodec/allcodecs.c
> +++ b/libavcodec/allcodecs.c
> @@ -407,6 +407,7 @@ void avcodec_register_all(void)
>      REGISTER_ENCDEC  (DVDSUB, dvdsub);
>      REGISTER_DECODER (JACOSUB, jacosub);
>      REGISTER_DECODER (MICRODVD, microdvd);
> +    REGISTER_DECODER (MOVTEXT, movtext);
>      REGISTER_DECODER (PGSSUB, pgssub);
>      REGISTER_DECODER (REALTEXT, realtext);
>      REGISTER_DECODER (SAMI, sami);
> diff --git a/libavcodec/movtextdec.c b/libavcodec/movtextdec.c
> new file mode 100644
> index 0000000..2cf072a
> --- /dev/null
> +++ b/libavcodec/movtextdec.c
> @@ -0,0 +1,106 @@
> +/*
> + * 3GPP TS 26.245 Timed Text decoder
> + * Copyright (c) 2012  Philip Langdale <philipl at overt.org>
> + *
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include "avcodec.h"
> +#include "ass.h"
> +#include "libavutil/avstring.h"
> +#include "libavutil/common.h"
> +#include "libavutil/bprint.h"
> +#include "libavutil/intreadwrite.h"
> +
> +static int text_to_ass(AVBPrint *buf, const char *text, const char *text_end)
> +{
> +    while (text < text_end) {
> +        switch (*text) {
> +        case '\r':
> +            break;
> +        case '\n':
> +            av_bprintf(buf, "\\N");
> +            break;
> +        default:
> +            av_bprint_chars(buf, *text, 1);
> +            break;
> +        }
> +        text++;
> +    }
> +
> +    av_bprintf(buf, "\r\n");
> +    return 0;
> +}
> +
> +static int mov_text_init(AVCodecContext *avctx) {
> +    /*
> +     * TODO: Handle the default text style.
> +     * NB: Most players ignore styles completely, with the result that
> +     * it's very common to find files where the default style is broken
> +     * and respecting it results in a worse experience than ignoring it.
> +     */
> +    return ff_ass_subtitle_header_default(avctx);
> +}
> +
> +static int mov_text_decode_frame(AVCodecContext *avctx,
> +                            void *data, int *got_sub_ptr, AVPacket *avpkt)
> +{
> +    AVSubtitle *sub = data;
> +    int ts_start, ts_end;
> +    AVBPrint buf;
> +    const char *ptr = avpkt->data;
> +    const char *end;
> +
> +    if (!ptr || avpkt->size <= 2)
> +        return 0;
> +
> +    /*
> +     * The first two bytes of the packet are the length of the text string
> +     * In complex cases, there are style descriptors appended to the string
> +     * so we can't just assume the packet size is the string size.
> +     */
> +    end = ptr + FFMAX(2 + AV_RB16(ptr), avpkt->size);
> +    ptr += 2;
> +
> +    ts_start = av_rescale_q(avpkt->pts,
> +                            avctx->time_base,
> +                            (AVRational){1,100});
> +    ts_end   = av_rescale_q(avpkt->pts + avpkt->duration,
> +                            avctx->time_base,
> +                            (AVRational){1,100});
> +
> +    // Note that the spec recommends lines be no longer than 2048 characters.
> +    av_bprint_init(&buf, 0, 65536);

It could overflow due to the final "\r\n", and possibly also due to \n ->
\\N, even though, with the \r, this one should be neutral. IMHO, it is best
to go with simply -1.

> +    text_to_ass(&buf, ptr, end);
> +
> +    if (!av_bprint_is_complete(&buf))
> +        av_log(avctx, AV_LOG_WARNING, "Subtitle truncated");
> +

I believe it usually result in "return AVERROR(ENOMEM)" and not just a
warning.

> +    ff_ass_add_rect(sub, buf.str, ts_start, ts_end-ts_start, 0);
> +    *got_sub_ptr = sub->num_rects > 0;
> +    av_bprint_finalize(&buf, NULL);
> +    return avpkt->size;
> +}
> +
> +AVCodec ff_movtext_decoder = {
> +    .name         = "mov_text",
> +    .long_name    = NULL_IF_CONFIG_SMALL("3GPP Timed Text subtitle"),
> +    .type         = AVMEDIA_TYPE_SUBTITLE,
> +    .id           = CODEC_ID_MOV_TEXT,
> +    .init         = mov_text_init,
> +    .decode       = mov_text_decode_frame,
> +};
> diff --git a/libavcodec/version.h b/libavcodec/version.h
> index 64c1dc6..c513607 100644
> --- a/libavcodec/version.h
> +++ b/libavcodec/version.h
> @@ -27,7 +27,7 @@
>   */
>  
>  #define LIBAVCODEC_VERSION_MAJOR 54
> -#define LIBAVCODEC_VERSION_MINOR  33
> +#define LIBAVCODEC_VERSION_MINOR  34
>  #define LIBAVCODEC_VERSION_MICRO 100
>  
>  #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
> diff --git a/tests/fate/subtitles.mak b/tests/fate/subtitles.mak
> index f2a68e1..92322da 100644
> --- a/tests/fate/subtitles.mak
> +++ b/tests/fate/subtitles.mak
> @@ -13,5 +13,8 @@ fate-sub-srt: CMD = md5 -i $(SAMPLES)/sub/SubRip_capability_tester.srt -f ass
>  FATE_SUBTITLES += fate-sub-realtext
>  fate-sub-realtext: CMD = md5 -i $(SAMPLES)/sub/RealText_capability_tester.rt -f ass
>  
> +FATE_SUBTITLES += fate-sub-movtext
> +fate-sub-movtext: CMD = md5 -i $(SAMPLES)/sub/MovText_capability_tester.mp4 -f ass
> +
>  FATE_SAMPLES_FFMPEG += $(FATE_SUBTITLES)
>  fate-subtitles: $(FATE_SUBTITLES)
> diff --git a/tests/ref/fate/sub-movtext b/tests/ref/fate/sub-movtext
> new file mode 100644
> index 0000000..d91c243
> --- /dev/null
> +++ b/tests/ref/fate/sub-movtext
> @@ -0,0 +1 @@
> +21453e8ddbbe35d1368a99fe563c969d

No other remarks from me, and the remarks above were really minor.

Regards,

-- 
  Nicolas George
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