[FFmpeg-devel] [PATCH] avcodec: add minimal teletext subtitle decoder
Aman Gupta
aman at tmm1.net
Thu Apr 26 07:18:32 EEST 2018
On Tue, Apr 24, 2018 at 7:08 PM Aman Gupta <ffmpeg at tmm1.net> wrote:
> From: Aman Gupta <aman at tmm1.net>
>
> Based largely on VLC's modules/codec/telx.c.
>
> Processes only teletext pages marked as subtitles, so depending
> on the stream it might not produce any output.
>
> Subtitles are rendered directly to ASS, with support for background
> colors and a best-effort at screen positioning.
This was meant to say foreground (text) colors. Background colors are not
implemented.
The ASS packets
> are emitted in real time (similar to ccaption_dec's real_time
> option), with -1 durations. The decoder expects that the player
> will remove all existing subtitles whenever a new packet arrives.
>
> The teletext clear command is implemented using an empty subtitle,
> which removes existing subtitles but does not render anything new.
> ---
> libavcodec/Makefile | 1 +
> libavcodec/allcodecs.c | 1 +
> libavcodec/teletextsubdec.c | 522
> ++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 524 insertions(+)
> create mode 100644 libavcodec/teletextsubdec.c
>
> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> index 4b8ad121db..83f2eab513 100644
> --- a/libavcodec/Makefile
> +++ b/libavcodec/Makefile
> @@ -593,6 +593,7 @@ OBJS-$(CONFIG_SVQ1_DECODER) += svq1dec.o
> svq1.o svq13.o h263data.o
> OBJS-$(CONFIG_SVQ1_ENCODER) += svq1enc.o svq1.o h263data.o \
> h263.o ituh263enc.o
> OBJS-$(CONFIG_SVQ3_DECODER) += svq3.o svq13.o mpegutils.o
> h264data.o
> +OBJS-$(CONFIG_TELETEXTSUB_DECODER) += teletextsubdec.o ass.o
> OBJS-$(CONFIG_TEXT_DECODER) += textdec.o ass.o
> OBJS-$(CONFIG_TEXT_ENCODER) += srtenc.o ass_split.o
> OBJS-$(CONFIG_TAK_DECODER) += takdec.o tak.o takdsp.o
> diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
> index 4d4ef530e4..f0f23eccef 100644
> --- a/libavcodec/allcodecs.c
> +++ b/libavcodec/allcodecs.c
> @@ -634,6 +634,7 @@ extern AVCodec ff_subrip_encoder;
> extern AVCodec ff_subrip_decoder;
> extern AVCodec ff_subviewer_decoder;
> extern AVCodec ff_subviewer1_decoder;
> +extern AVCodec ff_teletextsub_decoder;
> extern AVCodec ff_text_encoder;
> extern AVCodec ff_text_decoder;
> extern AVCodec ff_vplayer_decoder;
> diff --git a/libavcodec/teletextsubdec.c b/libavcodec/teletextsubdec.c
> new file mode 100644
> index 0000000000..f5f0f935ef
> --- /dev/null
> +++ b/libavcodec/teletextsubdec.c
> @@ -0,0 +1,522 @@
> +/*
> + * Minimal Teletext subtitle decoding for ffmpeg
> + * Copyright (c) 2018 Aman Gupta
> + * Copyright (c) 2013 Marton Balint
> + * Copyright (c) 2005-2010, 2012 Wolfram Gloger
> + * Copyright (c) 2007 Vincent Penne, VLC authors and VideoLAN
> (modules/codec/telx.c)
> + * Copyright (c) 2001-2005 dvb.matt, ProjectX java dvb decoder
> + *
> + * This library 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 of the License, or (at your option) any later version.
> + *
> + * This library 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 this library; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street
> <https://maps.google.com/?q=51+Franklin+Street&entry=gmail&source=g>,
> Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include <stdbool.h>
> +#include "avcodec.h"
> +#include "libavcodec/ass.h"
> +#include "libavcodec/dvbtxt.h"
> +#include "libavutil/opt.h"
> +#include "libavutil/bprint.h"
> +#include "libavutil/internal.h"
> +#include "libavutil/intreadwrite.h"
> +#include "libavutil/log.h"
> +#include "libavutil/reverse.h"
> +
> +#define NUM_ROWS 24
> +#define ROW_SIZE 40
> +#define NUM_MAGAZINES 9
> +
> +typedef struct TeletextContext
> +{
> + AVClass *class;
> + int64_t pts;
> + AVBPrint buffer;
> + int readorder;
> +
> + uint8_t rows[NUM_ROWS][ROW_SIZE];
> + bool active[NUM_MAGAZINES];
> + int charset;
> +} TeletextContext;
> +
> +/*
> + * My doc only mentions 13 national characters, but experiments show there
> + * are more, in france for example I already found two more (0x9 and 0xb).
> + *
> + * Conversion is in this order :
> + *
> + * 0x23 0x24 0x40 0x5b 0x5c 0x5d 0x5e 0x5f 0x60 0x7b 0x7c 0x7d 0x7e
> + * (these are the standard ones)
> + * 0x08 0x09 0x0a 0x0b 0x0c 0x0d (apparently a control character) 0x0e
> 0x0f
> + */
> +static const uint16_t national_charsets[][20] = {
> + { 0x00a3, 0x0024, 0x0040, 0x00ab, 0x00bd, 0x00bb, 0x005e, 0x0023,
> + 0x002d, 0x00bc, 0x00a6, 0x00be, 0x00f7 }, /* english ,000 */
> +
> + { 0x00e9, 0x00ef, 0x00e0, 0x00eb, 0x00ea, 0x00f9, 0x00ee, 0x0023,
> + 0x00e8, 0x00e2, 0x00f4, 0x00fb, 0x00e7, 0, 0x00eb, 0, 0x00ef }, /*
> french ,001 */
> +
> + { 0x0023, 0x00a4, 0x00c9, 0x00c4, 0x00d6, 0x00c5, 0x00dc, 0x005f,
> + 0x00e9, 0x00e4, 0x00f6, 0x00e5, 0x00fc }, /*
> swedish,finnish,hungarian ,010 */
> +
> + { 0x0023, 0x016f, 0x010d, 0x0165, 0x017e, 0x00fd, 0x00ed, 0x0159,
> + 0x00e9, 0x00e1, 0x011b, 0x00fa, 0x0161 }, /* czech,slovak ,011 */
> +
> + { 0x0023, 0x0024, 0x00a7, 0x00c4, 0x00d6, 0x00dc, 0x005e, 0x005f,
> + 0x00b0, 0x00e4, 0x00f6, 0x00fc, 0x00df }, /* german ,100 */
> +
> + { 0x00e7, 0x0024, 0x00a1, 0x00e1, 0x00e9, 0x00ed, 0x00f3, 0x00fa,
> + 0x00bf, 0x00fc, 0x00f1, 0x00e8, 0x00e0 }, /* portuguese,spanish
> ,101 */
> +
> + { 0x00a3, 0x0024, 0x00e9, 0x00b0, 0x00e7, 0x00bb, 0x005e, 0x0023,
> + 0x00f9, 0x00e0, 0x00f2, 0x00e8, 0x00ec }, /* italian ,110 */
> +
> + { 0x0023, 0x00a4, 0x0162, 0x00c2, 0x015e, 0x0102, 0x00ce, 0x0131,
> + 0x0163, 0x00e2, 0x015f, 0x0103, 0x00ee }, /* rumanian ,111 */
> +
> + /* I have these tables too, but I don't know how they can be
> triggered */
> + { 0x0023, 0x0024, 0x0160, 0x0117, 0x0119, 0x017d, 0x010d, 0x016b,
> + 0x0161, 0x0105, 0x0173, 0x017e, 0x012f }, /* lettish,lithuanian
> ,1000 */
> +
> + { 0x0023, 0x0144, 0x0105, 0x005a, 0x015a, 0x0141, 0x0107, 0x00f3,
> + 0x0119, 0x017c, 0x015b, 0x0142, 0x017a }, /* polish, 1001 */
> +
> + { 0x0023, 0x00cb, 0x010c, 0x0106, 0x017d, 0x0110, 0x0160, 0x00eb,
> + 0x010d, 0x0107, 0x017e, 0x0111, 0x0161 }, /*
> serbian,croatian,slovenian, 1010 */
> +
> + { 0x0023, 0x00f5, 0x0160, 0x00c4, 0x00d6, 0x017e, 0x00dc, 0x00d5,
> + 0x0161, 0x00e4, 0x00f6, 0x017e, 0x00fc }, /* estonian ,1011 */
> +
> + { 0x0054, 0x011f, 0x0130, 0x015e, 0x00d6, 0x00c7, 0x00dc, 0x011e,
> + 0x0131, 0x015f, 0x00f6, 0x00e7, 0x00fc }, /* turkish ,1100 */
> +};
> +
> +static const char *color_mappings[8] = {
> + "{\\c&H000000&}", // black
> + "{\\c&H0000FF&}", // red
> + "{\\c&H00FF00&}", // green
> + "{\\c&H00FFFF&}", // yellow
> + "{\\c&HFF0000&}", // blue
> + "{\\c&HFF00FF&}", // magenta
> + "{\\c&HFFFF00&}", // cyan
> + "{\\c&HFFFFFF&}" // white
> +};
> +
> +static int hamming(int a)
> +{
> + switch (a) {
> + case 0xA8: return 0;
> + case 0x0B: return 1;
> + case 0x26: return 2;
> + case 0x85: return 3;
> + case 0x92: return 4;
> + case 0x31: return 5;
> + case 0x1C: return 6;
> + case 0xBF: return 7;
> + case 0x40: return 8;
> + case 0xE3: return 9;
> + case 0xCE: return 10;
> + case 0x6D: return 11;
> + case 0x7A: return 12;
> + case 0xD9: return 13;
> + case 0xF4: return 14;
> + case 0x57: return 15;
> + default: return -1; // decoding error , not yet corrected
> + }
> +}
> +
> +// ucs-2 --> utf-8
> +// this is not a general function, but it's enough for what we do here
> +// the result buffer need to be at least 4 bytes long
> +static void to_utf8(char *res, uint16_t ch)
> +{
> + if (ch >= 0x80) {
> + if (ch >= 0x800) {
> + res[0] = (ch >> 12) | 0xE0;
> + res[1] = ((ch >> 6) & 0x3F) | 0x80;
> + res[2] = (ch & 0x3F) | 0x80;
> + res[3] = 0;
> + } else {
> + res[0] = (ch >> 6) | 0xC0;
> + res[1] = (ch & 0x3F) | 0x80;
> + res[2] = 0;
> + }
> + } else {
> + res[0] = ch;
> + res[1] = 0;
> + }
> +}
> +
> +static void decode_string(AVCodecContext *avctx, AVBPrint *buf,
> + const uint8_t *packet, int *leading, int *olen)
> +{
> + TeletextContext *ctx = avctx->priv_data;
> + int i, len = 0;
> + int end_box = 0;
> + bool char_seen = false;
> + char utf8[7];
> + const uint16_t *charset = national_charsets[ctx->charset];
> + av_bprint_clear(buf);
> + *leading = 0;
> +
> + for (i = 0; i < ROW_SIZE; i++) {
> + int in = ff_reverse[packet[i]] & 0x7f;
> + uint16_t out = 32;
> +
> + switch (in) {
> + /* special national characters */
> + case 0x23: out = charset[0]; break;
> + case 0x24: out = charset[1]; break;
> + case 0x40: out = charset[2]; break;
> + case 0x5b: out = charset[3]; break;
> + case 0x5c: out = charset[4]; break;
> + case 0x5d: out = charset[5]; break;
> + case 0x5e: out = charset[6]; break;
> + case 0x5f: out = charset[7]; break;
> + case 0x60: out = charset[8]; break;
> + case 0x7b: out = charset[9]; break;
> + case 0x7c: out = charset[10]; break;
> + case 0x7d: out = charset[11]; break;
> + case 0x7e: out = charset[12]; break;
> +
> + /* control codes */
> + case 0xd:
> + i++;
> + in = ff_reverse[packet[i]] & 0x7f;
> + if (in == 0xb)
> + in = 7;
> + if (in >= 0 && in < 8) {
> + av_bprintf(buf, "%s", color_mappings[in]);
> + }
> + continue;
> +
> + case 0xa:
> + end_box++;
> + if (end_box == 1)
> + continue;
> + break;
> +
> + case 0xb:
> + continue;
> +
> + /* color codes */
> + case 0x0:
> + case 0x1:
> + case 0x2:
> + case 0x3:
> + case 0x4:
> + case 0x5:
> + case 0x6:
> + case 0x7:
> + av_bprintf(buf, "%s", color_mappings[in]);
> + break;
> +
> + default:
> + /* non documented national range 0x08 - 0x0f */
> + if (in >= 0x08 && in <= 0x0f) {
> + out = charset[13 + in - 8];
> + break;
> + }
> +
> + /* normal ascii */
> + if (in >= 32 && in < 0x7f)
> + out = in;
> + }
> +
> + if (end_box == 2)
> + break;
> +
> + /* handle undefined national characters */
> + if (out == 0)
> + out = 32;
> +
> + if (out == 32 && !char_seen)
> + (*leading)++;
> + else if (out != 32)
> + char_seen = true;
> +
> + /* convert to utf-8 */
> + to_utf8(utf8, out);
> + av_bprintf(buf, "%s", utf8);
> +
> + if (char_seen || out != 32)
> + len += strlen(utf8);
> + }
> +
> + /* remove trailing spaces */
> + for (i = buf->len-1; i >= 0 && buf->str[i] == 32; i--)
> + ;
> + buf->str[i+1] = 0;
> + buf->len = i;
> +
> + *olen = len;
> +}
> +
> +static int teletext_init_decoder(AVCodecContext *avctx)
> +{
> + TeletextContext *ctx = avctx->priv_data;
> + av_bprint_init(&ctx->buffer, 0, AV_BPRINT_SIZE_UNLIMITED);
> + ctx->pts = AV_NOPTS_VALUE;
> + return ff_ass_subtitle_header(avctx,
> + "Monospace",
> + ASS_DEFAULT_FONT_SIZE,
> + ASS_DEFAULT_COLOR,
> + ASS_DEFAULT_BACK_COLOR,
> + ASS_DEFAULT_BOLD,
> + ASS_DEFAULT_ITALIC,
> + ASS_DEFAULT_UNDERLINE,
> + 3,
> + ASS_DEFAULT_ALIGNMENT);
> +}
> +
> +static int teletext_close_decoder(AVCodecContext *avctx)
> +{
> + TeletextContext *ctx = avctx->priv_data;
> + ctx->pts = AV_NOPTS_VALUE;
> + av_bprint_finalize(&ctx->buffer, NULL);
> + return 0;
> +}
> +
> +static void teletext_flush(AVCodecContext *avctx)
> +{
> + TeletextContext *ctx = avctx->priv_data;
> + int i;
> + ctx->pts = AV_NOPTS_VALUE;
> + if (!(avctx->flags2 & AV_CODEC_FLAG2_RO_FLUSH_NOOP))
> + ctx->readorder = 0;
> + for (i = 0; i < NUM_ROWS; i++)
> + ctx->rows[i][0] = 0;
> + av_bprint_clear(&ctx->buffer);
> +}
> +
> +static int capture_screen(AVCodecContext *avctx)
> +{
> + TeletextContext *ctx = avctx->priv_data;
> + int i, j;
> + int tab = 0;
> + int num_rows = 0;
> + bool align_center = false, align_right = false;
> + bool maybe_center = false;
> + char prev_line[128] = {0};
> + AVBPrint line;
> + av_bprint_init(&line, 0, AV_BPRINT_SIZE_UNLIMITED);
> + av_bprint_clear(&ctx->buffer);
> +
> + for (i = 0; i < NUM_ROWS; i++) {
> + int leading, len;
> + int spaces = 0;
> + const uint8_t *row = ctx->rows[i];
> + if (row[0] == 0)
> + continue;
> + num_rows++;
> +
> + av_bprint_clear(&line);
> + decode_string(avctx, &line, row, &leading, &len);
> +
> + // av_log(avctx, AV_LOG_DEBUG, "line[%d]: '%s' [leading=%d,
> len=%d]\n",
> + // i, line.str, leading, len);
> +
> + for (j = 0; j < line.len; j++) {
> + if (line.str[j] == ' ')
> + spaces++;
> + else
> + break;
> + }
> +
> + if (!tab || spaces < tab)
> + tab = spaces;
> +
> + if (leading > 0 && leading + len > 35)
> + align_right = true;
> + else if (leading > 0 && leading*2 + len <= 36)
> + align_center = true;
> + else if (leading == 0 && len == 34)
> + maybe_center = true;
> + }
> +
> + if (num_rows == 1 && maybe_center)
> + align_center = true;
> +
> + for (i = 0; i < NUM_ROWS; i++) {
> + int leading, len;
> + int x, y, alignment = 7;
> + const uint8_t *row = ctx->rows[i];
> + bool char_seen = false;
> + if (row[0] == 0)
> + continue;
> +
> + av_bprint_clear(&line);
> + decode_string(avctx, &line, row, &leading, &len);
> +
> + len = FFMIN(sizeof(prev_line), line.len+1);
> + if (strncmp(prev_line, line.str, len) == 0)
> + continue;
> + strncpy(prev_line, line.str, len);
> +
> + /* skip leading space */
> + j = 0;
> + while (line.str[j] == ' ' && j < tab)
> + j++;
> +
> + x = ASS_DEFAULT_PLAYRESX * (0.1 + (0.80 / 34) * j);
> + y = ASS_DEFAULT_PLAYRESY * (0.1 + (0.80 / 25) * i);
> +
> + if (align_center) {
> + x = ASS_DEFAULT_PLAYRESX * 0.5;
> + alignment = 8;
> + } else if (align_right) {
> + x = ASS_DEFAULT_PLAYRESX * 0.9;
> + alignment = 9;
> + }
> +
> + av_bprintf(&ctx->buffer, "{\\an%d}{\\pos(%d,%d)}", alignment, x,
> y);
> + for (; j <= line.len; j++) {
> + if (line.str[j] == 32 && !char_seen && !align_center &&
> !align_right)
> + av_bprintf(&ctx->buffer, "\\h");
> + else {
> + av_bprintf(&ctx->buffer, "%c", line.str[j]);
> + char_seen = true;
> + }
> + }
> + av_bprintf(&ctx->buffer, "\\N");
> + }
> +
> + av_bprint_finalize(&line, NULL);
> + if (!av_bprint_is_complete(&ctx->buffer))
> + return AVERROR(ENOMEM);
> + return 0;
> +}
> +
> +static int teletext_decode_frame(AVCodecContext *avctx, void *data, int
> *got_sub, AVPacket *pkt)
> +{
> + TeletextContext *ctx = avctx->priv_data;
> + AVSubtitle *sub = data;
> + int ret = 0;
> + int offset = 0;
> + bool updated = false, erased = false;
> +
> + if (avctx->pkt_timebase.num && pkt->pts != AV_NOPTS_VALUE)
> + ctx->pts = av_rescale_q(pkt->pts, avctx->pkt_timebase,
> AV_TIME_BASE_Q);
> +
> + if (pkt->size) {
> + const int full_pes_size = pkt->size + 45; /* PES header is 45
> bytes */
> +
> + // We allow unreasonably big packets, even if the standard only
> allows a max size of 1472
> + if (full_pes_size < 184 || full_pes_size > 65504 || full_pes_size
> % 184 != 0)
> + return AVERROR_INVALIDDATA;
> +
> + if (!ff_data_identifier_is_teletext(*pkt->data))
> + return pkt->size;
> +
> + for (offset = 1; offset + 46 <= pkt->size; offset += 46) {
> + int mpag, row, magazine;
> + uint8_t *packet = pkt->data + offset;
> + if (packet[0] == 0xFF)
> + continue;
> +
> + mpag = (hamming(packet[4]) << 4) | hamming(packet[5]);
> + if (mpag < 0)
> + continue;
> +
> + row = 0xFF & ff_reverse[mpag];
> + magazine = 7 & row;
> + if (magazine == 0)
> + magazine = 8;
> + row >>= 3;
> +
> + if (row == 0) { // row 0: flags and header line
> + int flag = 0;
> + int i, page, f_charset;
> + bool f_erase, f_subtitle, f_inhibit, f_suppress,
> f_update, f_news;
> +
> + for (i = 0; i < 6; i++)
> + flag |= (0xF & (ff_reverse[hamming(packet[8+i])] >>
> 4)) << (4*i);
> +
> + page = (0xF0 & ff_reverse[hamming(packet[7])] ) |
> + (0x0F & (ff_reverse[hamming(packet[6])] >> 4));
> +
> + f_erase = 1 & (flag>>7);
> + f_news = 1 & (flag>>15);
> + f_subtitle = 1 & (flag>>15);
> + f_suppress = 1 & (flag>>16);
> + f_update = 1 & (flag>>17);
> + f_inhibit = 1 & (flag>>19);
> + f_charset = 7 & (flag>>21);
> +
> + ctx->active[magazine] = f_subtitle;
> + if (!ctx->active[magazine])
> + continue;
> +
> + ctx->charset = f_charset;
> +
> + // av_log(avctx, AV_LOG_DEBUG, "magazine=%d page=%d
> erase=%d subtitle=%d news=%d charset=%d inhibit=%d suppress=%d update=%d\n",
> + // magazine, page, f_erase, f_subtitle, f_news,
> f_charset, f_inhibit, f_suppress, f_update);
> +
> + if (f_erase) {
> + for (i = 0; i < NUM_ROWS; i++)
> + ctx->rows[i][0] = 0;
> + erased = true;
> + continue;
> + }
> +
> + } else if (row < 24) { // row 1-23: normal lines
> + if (!ctx->active[magazine])
> + continue;
> + if (memcmp(ctx->rows[row], packet+6, ROW_SIZE) != 0) {
> + updated |= true;
> + memcpy(ctx->rows[row], packet+6, ROW_SIZE);
> + }
> +
> + // int j;
> + // av_log(avctx, AV_LOG_DEBUG, "row[%d]: ", row);
> + // for (j = 0; j < ROW_SIZE; j++) {
> + // int in = ff_reverse[ctx->rows[row][j]] & 0x7f;
> + // av_log(avctx, AV_LOG_DEBUG, "0x%x ", in);
> + // }
> + // av_log(avctx, AV_LOG_DEBUG, "\n");
> + }
> + }
> + }
> +
> + if (updated || (erased && ctx->buffer.len)) {
> + ret = capture_screen(avctx);
> + if (ret < 0)
> + return ret;
> + ret = ff_ass_add_rect(sub, ctx->buffer.str, ctx->readorder++, 0,
> NULL, NULL);
> + if (ret < 0)
> + return ret;
> + sub->end_display_time = -1;
> + }
> +
> + *got_sub = sub->num_rects > 0;
> + return offset;
> +}
> +
> +static const AVClass teletext_class = {
> + .class_name = "teletextsub",
> + .item_name = av_default_item_name,
> + .version = LIBAVUTIL_VERSION_INT,
> +};
> +
> +AVCodec ff_teletextsub_decoder = {
> + .name = "teletext_subtitle",
> + .long_name = NULL_IF_CONFIG_SMALL("Minimal DVB teletext subtitle
> decoder"),
> + .type = AVMEDIA_TYPE_SUBTITLE,
> + .id = AV_CODEC_ID_DVB_TELETEXT,
> + .priv_data_size = sizeof(TeletextContext),
> + .init = teletext_init_decoder,
> + .close = teletext_close_decoder,
> + .decode = teletext_decode_frame,
> + .capabilities = AV_CODEC_CAP_DELAY,
> + .flush = teletext_flush,
> + .priv_class= &teletext_class,
> +};
> --
> 2.14.2
>
>
More information about the ffmpeg-devel
mailing list