[FFmpeg-devel] [PATCH 2/2] Adding closed caption decoder
Anshul
anshul.ffmpeg at gmail.com
Tue Dec 30 15:16:29 CET 2014
On 12/12/2014 04:23 PM, Anshul wrote:
> On 12/06/2014 04:24 PM, Anshul wrote:
>> On 12/06/2014 04:22 PM, Anshul wrote:
>>> On 12/05/2014 07:56 PM, Nicolas George wrote:
>>>> Hi. I had time to look at the code with some more details. Comments are
>>>> below.
>>>>
>>>>> >From 31f69ccfb45247a7cc203084a931b8523284aa13 Mon Sep 17 00:00:00 2001
>>>>> From: Anshul Maheshwari <anshul.ffmpeg at gmail.com>
>>>>> Date: Wed, 3 Dec 2014 23:37:22 +0530
>>>>> Subject: [PATCH 2/2] Adding Closed caption Decoder
>>>>>
>>>>> ---
>>>>> libavcodec/Makefile | 1 +
>>>>> libavcodec/allcodecs.c | 1 +
>>>>> libavcodec/ccaption_dec.c | 318 ++++++++++++++++++++++++++++++++++++++++++++++
>>>>> 3 files changed, 320 insertions(+)
>>>>> create mode 100644 libavcodec/ccaption_dec.c
>>>>>
>>>>> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
>>>>> index fa0f53d..bbc516d 100644
>>>>> --- a/libavcodec/Makefile
>>>>> +++ b/libavcodec/Makefile
>>>>> @@ -173,6 +173,7 @@ OBJS-$(CONFIG_BRENDER_PIX_DECODER) += brenderpix.o
>>>>> OBJS-$(CONFIG_C93_DECODER) += c93.o
>>>>> OBJS-$(CONFIG_CAVS_DECODER) += cavs.o cavsdec.o cavsdsp.o \
>>>>> cavsdata.o mpeg12data.o
>>>>> +OBJS-$(CONFIG_CCAPTION_DECODER) += ccaption_dec.o
>>>>> OBJS-$(CONFIG_CDGRAPHICS_DECODER) += cdgraphics.o
>>>>> OBJS-$(CONFIG_CDXL_DECODER) += cdxl.o
>>>>> OBJS-$(CONFIG_CINEPAK_DECODER) += cinepak.o
>>>>> diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
>>>>> index 0d39d33..8c07388 100644
>>>>> --- a/libavcodec/allcodecs.c
>>>>> +++ b/libavcodec/allcodecs.c
>>>>> @@ -480,6 +480,7 @@ void avcodec_register_all(void)
>>>>> /* subtitles */
>>>>> REGISTER_ENCDEC (SSA, ssa);
>>>>> REGISTER_ENCDEC (ASS, ass);
>>>>> + REGISTER_DECODER(CCAPTION, ccaption);
>>>>> REGISTER_ENCDEC (DVBSUB, dvbsub);
>>>>> REGISTER_ENCDEC (DVDSUB, dvdsub);
>>>>> REGISTER_DECODER(JACOSUB, jacosub);
>>>>> diff --git a/libavcodec/ccaption_dec.c b/libavcodec/ccaption_dec.c
>>>>> new file mode 100644
>>>>> index 0000000..0a7dfd8
>>>>> --- /dev/null
>>>>> +++ b/libavcodec/ccaption_dec.c
>>>>> @@ -0,0 +1,318 @@
>>>>> +/*
>>>>> + * Closed Caption Decoding
>>>>> + * Copyright (c) 2014 Anshul Maheshwari
>>>>> + *
>>>>> + * 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"
>>>>> +
>>>>> +#define SCREEN_ROWS 15
>>>>> +#define SCREEN_COLUMNS 32
>>>>> +
>>>>> +#define SET_FLAG(var, val) ( var |= ( 1 << (val) ) )
>>>>> +#define UNSET_FLAG(var, val) ( var &= ~( 1 << (val)) )
>>>>> +#define CHECK_FLAG(var, val) ( (var) & (1 << (val) ) )
>>>>> +
>>>>> +enum cc_mode {
>>>>> + CCMODE_POPON,
>>>>> + CCMODE_PAINTON,
>>>>> + CCMODE_ROLLUP_2,
>>>>> + CCMODE_ROLLUP_3,
>>>>> + CCMODE_ROLLUP_4,
>>>>> + CCMODE_TEXT,
>>>>> +};
>>>>> +
>>>>> +struct Screen {
>>>>> + uint8_t characters[SCREEN_ROWS][SCREEN_COLUMNS+1];
>>>> Maybe add a comment about the +1?
>>> done
>>>>> + /*
>>>>> + * row used flag will be 0 when none in use other wise it will have its
>>>>> + * corrosponding bit high.
>>>> Language nit. I suggest: "Bitmask of used rows; if a bit is not set, the
>>>> corresponding row is not used."
>>> done
>>>>> + * for setting row 1 use row | (1 >> 1)
>>>>> + * for setting row 15 use row | (1 >> 15)
>>>> Are you sure that is ">>" and not "<<"? And is it a good idea to number
>>>> starting from 1?
>>> It was just commented in wrong way, corrected comment.
>>>>> + */
>>>>> + int16_t row_used;
>>>>> +};
>>>>> +
>>>>> +
>>>>> +typedef struct CCaptionSubContext {
>>>>> + int parity_table[256];
>>>>> + int row_cnt;
>>>>> + struct Screen screen[2];
>>>>> + int active_screen;
>>>>> + int cursor_row;
>>>>> + int cursor_column;
>>>>> + AVBPrint buffer;
>>>>> + /* erase display memory */
>>>>> + int edm;
>>>> It is used only a handful of times: I suggest a more meaningful name instead
>>>> of a comment: "erase_disp_mem" for example.
>>> done
>>>>> + int rollup;
>>>>> + enum cc_mode mode;
>>>>> + int64_t start_time;
>>>>> + /* visible screen time */
>>>>> + int64_t startv_time;
>>>> Is the v a typo?
>>> no it was written to express v = visible, (visible screen start time)
>>>>> + int64_t end_time;
>>>>> + char prev_cmd[2];
>>>> The code uses various types for these values: char, unsigned char, uint8_t.
>>>> I suggest to stick with uint8_t if it works.
>>> changed unsigned char to uint8_t
>>>>> +}CCaptionSubContext;
>>>>> +
>>>>> +static void build_parity_table(int *parity_table)
>>>>> +{
>>>>> + unsigned int byte;
>>>> Inconsistent indentation.
>>> corrected
>>>>> + int parity_v;
>>>>> + for (byte = 0; byte <= 127; byte++) {
>>>>> + parity_v = av_popcount(byte & 0x7f) & 1;
>>>> The & 0x7f is redundant.
>>> removed
>>>>> + parity_table[byte] = parity_v;
>>>>> + parity_table[byte | 0x80] = !parity_v;
>>>>> + }
>>>>> +}
>>>>> +
>>>>> +static av_cold int init_decoder(AVCodecContext *avctx)
>>>>> +{
>>>>> +
>>>>> + CCaptionSubContext *ctx = avctx->priv_data;
>>>>> +
>>>>> + build_parity_table(ctx->parity_table);
>>>>> + ctx->row_cnt = 0;
>>>>> + av_bprint_init(&ctx->buffer, 0, AV_BPRINT_SIZE_UNLIMITED);
>>>>> + ctx->edm = 0;
>>>>> + /* taking by default roll up to 2 */
>>>>> + ctx->rollup = 2;
>>>>> + /* set active screen as 0 */
>>>>> + ctx->active_screen = 0;
>>>>> + memset(ctx->prev_cmd,0,2);
>>>>> + ff_ass_subtitle_header_default(avctx);
>>>> All the "= 0" and the memset are unnecessary.
>>> removed
>>>>> + return 0;
>>>>> +}
>>>>> +
>>>>> +static av_cold int close_decoder(AVCodecContext *avctx)
>>>>> +{
>>>>> + CCaptionSubContext *ctx = avctx->priv_data;
>>>>> + av_bprint_finalize( &ctx->buffer, NULL);
>>>>> + return 0;
>>>>> +}
>>>>> +
>>>>> +/**
>>>>> + * This function after validating parity bit, also remove it from data pair.
>>>>> + */
>>>>> +static int validate_cc_data_pair (unsigned char *cc_data_pair, int *parity_table)
>>>>> +{
>>>>> + unsigned char cc_valid = (*cc_data_pair & 4) >>2;
>>>>> + unsigned char cc_type = *cc_data_pair & 3;
>>>>> +
>>>>> + if (!cc_valid)
>>>>> + return -1;
>>>>> +
>>>>> + // if EIA-608 data then verify parity.
>>>>> + if (cc_type==0 || cc_type==1) {
>>>>> + if (!parity_table[cc_data_pair[2]]) {
>>>>> + // If the second byte doesn't pass parity, ignore pair
>>>>> + return -1;
>>>> Meaningful error codes? AVERROR(EINVAL) or AVERROR_INVALID_DATA? Even when
>>>> they are not supposed to, the -1 have a habit of reaching the user. Same
>>>> below.
>>> done
>>>>> + }
>>>>> + if (!parity_table[cc_data_pair[1]]) {
>>>>> + // The first byte doesn't pass parity, we replace it with a solid blank
>>>>> + // and process the pair.
>>>>> + cc_data_pair[1]=0x7F;
>>>>> + }
>>>>> + }
>>>>> +
>>>>> + //Skip non-data
>>>>> + if( (cc_data_pair[0] == 0xFA || cc_data_pair[0] == 0xFC || cc_data_pair[0] == 0xFD )
>>>>> + && (cc_data_pair[1] & 0x7F) == 0 && (cc_data_pair[2] & 0x7F) == 0)
>>>>> + return -1;
>>>>> +
>>>>> + //skip 708 data
>>>>> + if(cc_type == 3 || cc_type == 2 )
>>>>> + return -1;
>>>>> +
>>>>> + /* remove parity bit */
>>>>> + cc_data_pair[1] &= 0x7F;
>>>>> + cc_data_pair[2] &= 0x7F;
>>>>> +
>>>>> +
>>>>> + return 0;
>>>>> +
>>>>> +}
>>>>> +static void handle_pac( CCaptionSubContext *ctx, uint8_t hi, uint8_t lo )
>>>>> +{
>>>>> + static const int row_map[] = {
>>>> Could be int8_t to save memory.
>>> done
>>>>> + 11, -1, 1, 2, 3, 4, 12, 13, 14, 15, 5, 6, 7, 8, 9, 10
>>>>> + };
>>>>> + const int index = ( (hi<<1) & 0x0e) | ( (lo>>5) & 0x01 );
>>>>> +
>>>> It looks like the values come from external data with subtle arithmetic, so
>>>> I suggest:
>>>>
>>>> av_assert2((unsigned)index < sizeof(row_map));
>>> I am using 3 bit from hi and 1 bit from lo data, so I am using total 4 bit
>>> which mean only 0-15 possible. and for unknown value not defined in spec
>>> I have kept the value as -1 on that index.
>>> so no need to check.
>>>>> + if( row_map[index] <= 0 )
>>>>> + return;
>>>>> +
>>>>> + ctx->cursor_row = row_map[index] - 1;
>>>>> + ctx->cursor_column = 0;
>>>>> +
>>>>> +}
>>>>> +
>>>>> +/**
>>>>> + * @param pts it is required to set end time
>>>>> + */
>>>>> +static void handle_edm(CCaptionSubContext *ctx,int64_t pts)
>>>>> +{
>>>>> + int i;
>>>>> + struct Screen *screen = ctx->screen + ctx->active_screen;
>>>>> +
>>>>> + ctx->start_time = ctx->startv_time;
>>>>> + for( i = 0; screen->row_used && i < SCREEN_ROWS; i++)
>>>>> + {
>>>>> + if(CHECK_FLAG(screen->row_used,i)) {
>>>>> + av_bprint_append_data(&ctx->buffer, screen->characters[i], strlen(screen->characters[i]));
>>>>> + av_bprint_append_data(&ctx->buffer, "\\N",2);
>>>>> + UNSET_FLAG(screen->row_used, i);
>>>>> + }
>>>>> + }
>>>>> + ctx->startv_time = pts;
>>>>> + ctx->edm = 1;
>>>>> + ctx->end_time = pts;
>>>>> +}
>>>>> +static void handle_eoc(CCaptionSubContext *ctx, int64_t pts)
>>>>> +{
>>>>> + ctx->active_screen = !ctx->active_screen;
>>>>> + ctx->startv_time = pts;
>>>>> +}
>>>>> +static struct Screen *get_writing_screen(CCaptionSubContext *ctx)
>>>>> +{
>>>>> + switch (ctx->mode) {
>>>>> + case CCMODE_POPON:
>>>>> + // use Inactive screen
>>>>> + return ctx->screen + !ctx->active_screen;
>>>>> + case CCMODE_PAINTON:
>>>>> + case CCMODE_ROLLUP_2:
>>>>> + case CCMODE_ROLLUP_3:
>>>>> + case CCMODE_ROLLUP_4:
>>>>> + case CCMODE_TEXT:
>>>>> + // use active screen
>>>>> + return ctx->screen + !ctx->active_screen;
>>>>> + }
>>>>> + /* It was never an option */
>>>>> + return NULL;
>>>>> +}
>>>>> +static void handle_char(CCaptionSubContext *ctx, char hi, char lo, int64_t pts)
>>>>> +{
>>>>> + struct Screen *screen = get_writing_screen(ctx);
>>>>> + char *row = screen->characters[ctx->cursor_row] + ctx->cursor_column;
>>>> Here too: av_assert0((unsigned)ctx->cursor_row < SCREEN_ROWS) and same for
>>>> column.
>>> We can never get row greater then SCREEN_ROWS, I have not implemented to
>>> read column value from pac. so left it as it is.
>>>>> +
>>>>> + SET_FLAG(screen->row_used,ctx->cursor_row);
>>>>> +
>>>>> + *row++ = hi;
>>>>> + ctx->cursor_column++;
>>>>> + if(lo) {
>>>>> + *row++ = lo;
>>>>> + ctx->cursor_column++;
>>>>> + }
>>>>> + *row = 0;
>>>>> + /* reset prev command since character can repeat */
>>>>> + ctx->prev_cmd[0] = 0;
>>>>> + ctx->prev_cmd[1] = 0;
>>>>> +}
>>>>> +static int process_cc608(CCaptionSubContext *ctx, int64_t pts, unsigned char hi, unsigned char lo)
>>>>> +{
>>>>> +
>>>>> +#define COR3(var, with1, with2, with3) ( (var) == (with1) || (var) == (with2) || (var) == (with3) )
>>>> It looks like you always use COR3(hi, 0x14, 0x15, 0x1C) exactly: is it on
>>>> purpose, a typo, or maybe can you simplify?
>>> These are done for purpose, I have to implement some other command which
>>> have
>>> different values to be compared. so not simplifying it.
>>>>> + if ( hi == ctx->prev_cmd[0] && lo == ctx->prev_cmd[1]) {
>>>>> + /* ignore redundant command */
>>>>> + } else if ( (hi == 0x10 && (lo >= 0x40 || lo <= 0x5f)) ||
>>>>> + ( (hi >= 0x11 && hi <= 0x17) && (lo >= 0x40 && lo <= 0x7f) ) ) {
>>>>> + handle_pac(ctx, hi, lo);
>>>>> + } else if ( COR3(hi, 0x14, 0x15, 0x1C) && lo == 0x20 ) {
>>>>> + /* resume caption loading */
>>>>> + ctx->mode = CCMODE_POPON;
>>>>> + } else if ( COR3(hi, 0x14, 0x15, 0x1C) && lo == 0x25 ) {
>>>>> + ctx->rollup = 2;
>>>>> + } else if ( COR3(hi, 0x14, 0x15, 0x1C) && lo == 0x26 ) {
>>>>> + ctx->rollup = 3;
>>>>> + } else if ( COR3(hi, 0x14, 0x15, 0x1C) && lo == 0x27 ) {
>>>>> + ctx->rollup = 4;
>>>>> + } else if ( COR3(hi, 0x14, 0x15, 0x1C) && lo == 0x29 ) {
>>>>> + /* resume direct captioning */
>>>>> + ctx->mode = CCMODE_PAINTON;
>>>>> + } else if ( COR3(hi, 0x14, 0x15, 0x1C) && lo == 0x2C ) {
>>>>> + /* erase display memory */
>>>>> + handle_edm(ctx, pts);
>>>>> + } else if ( COR3(hi, 0x14, 0x15, 0x1C) && lo == 0x2D ) {
>>>>> + /* carriage return */
>>>>> + ctx->row_cnt++;
>>>>> + if(ctx->row_cnt == ctx->rollup) {
>>>>> + ctx->row_cnt = 0;
>>>>> + handle_edm(ctx, pts);
>>>>> + }
>>>>> + } else if ( COR3(hi, 0x14, 0x15, 0x1C) && lo == 0x2F ) {
>>>>> + /* end of caption */
>>>>> + handle_eoc(ctx, pts);
>>>>> + } else if (hi>=0x20) {
>>>>> + /* Standard characters (always in pairs) */
>>>>> + handle_char(ctx, hi, lo, pts);
>>>>> + } else {
>>>>> + /* Ignoring all other non data code */
>>>>> + }
>>>>> +
>>>>> + /* set prev command */
>>>>> + ctx->prev_cmd[0] = hi;
>>>>> + ctx->prev_cmd[1] = lo;
>>>>> +
>>>>> +#undef COR3
>>>>> + return 0;
>>>>> +
>>>>> +}
>>>>> +static int decode(AVCodecContext *avctx, void *data, int *got_sub, AVPacket *avpkt)
>>>>> +{
>>>>> + CCaptionSubContext *ctx = avctx->priv_data;
>>>>> + AVSubtitle *sub = data;
>>>>> + unsigned char *bptr = avpkt->data;
>>>>> + int len = avpkt->size;
>>>>> + int ret = 0;
>>>>> + int i;
>>>>> +
>>>>> + for (i = 0; i < len; i += 3) {
>>>>> + unsigned char cc_type = *(bptr + i) & 3;
>>>>> + if (validate_cc_data_pair( bptr + i, ctx->parity_table ) )
>>>>> + continue;
>>>>> + /* ignoring data field 1 */
>>>>> + if(cc_type == 1)
>>>>> + continue;
>>>>> + else
>>>>> + process_cc608(ctx, avpkt->pts, *(bptr + i + 1), *(bptr + i + 2));
>>>>> + }
>>>>> + if(ctx->edm && *ctx->buffer.str)
>>>>> + {
>>>>> + int start_time = av_rescale_q(ctx->start_time, avctx->time_base, (AVRational){ 1, 100 });
>>>>> + int end_time = av_rescale_q(ctx->end_time, avctx->time_base, (AVRational){ 1, 100 });
>>>>> + ret = ff_ass_add_rect(sub, ctx->buffer.str, start_time, end_time - start_time , 0);
>>>>> a
>>>> You need to use av_bprint_is_complete() and return AVERROR(ENOMEM) if the
>>>> text was truncated.
>>> done in handle_edm
>>>>> + if (ret < 0)
>>>>> + return ret;
>>>>> + sub->pts = av_rescale_q(ctx->start_time, avctx->time_base, AV_TIME_BASE_Q);
>>>>> + ctx->edm = 0;
>>>>> + av_bprint_clear(&ctx->buffer);
>>>>> + }
>>>>> +
>>>>> + *got_sub = sub->num_rects > 0;
>>>>> + return 0;
>>>>> +}
>>>>> +
>>>>> +AVCodec ff_ccaption_decoder = {
>>>>> + .name = "cc_dec",
>>>>> + .long_name = NULL_IF_CONFIG_SMALL("Closed Caption Decoder"),
>>>> I suggest to have "EIA-608" and "CEA-708" appear in the name, for people
>>>> specifically looking for it: "Closed Caption (EIA-608 / CEA-708) Decoder"
>>>> maybe.
>>> done
>>>>> + .type = AVMEDIA_TYPE_SUBTITLE,
>>>>> + .id = AV_CODEC_ID_EIA_608,
>>>>> + .priv_data_size = sizeof(CCaptionSubContext),
>>>>> + .init = init_decoder,
>>>>> + .close = close_decoder,
>>>>> + .decode = decode,
>>>>> +};
>>>> Regards,
>>>>
>>> I have also removed some error which were causing to print nothing in
>>> subccItalic.mpg.
>>>
>>> Though subtitle is still not italic.
>>>
>>> I was thinking to put extra features in next iteration of patch.
>>>
>>> -Anshul
>>>
>> Attaching patch with those work.
> ping
>
> -please comment
> Anshul Maheshwari
ping
-Anshul
More information about the ffmpeg-devel
mailing list