[FFmpeg-devel] [PATCH 1/2] avcodec: add xbm parser

[James Almer]

On 2/3/2021 10:10 AM, Paul B Mahol wrote:
> Signed-off-by: Paul B Mahol <onemda at gmail.com>
> ---
>   libavcodec/Makefile     |   1 +
>   libavcodec/parsers.c    |   1 +
>   libavcodec/xbm_parser.c | 101 ++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 103 insertions(+)
>   create mode 100644 libavcodec/xbm_parser.c
> 
> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> index ab2e5ad308..2ddf021f04 100644
> --- a/libavcodec/Makefile
> +++ b/libavcodec/Makefile
> @@ -1127,6 +1127,7 @@ OBJS-$(CONFIG_VP3_PARSER)              += vp3_parser.o
>   OBJS-$(CONFIG_VP8_PARSER)              += vp8_parser.o
>   OBJS-$(CONFIG_VP9_PARSER)              += vp9_parser.o
>   OBJS-$(CONFIG_WEBP_PARSER)             += webp_parser.o
> +OBJS-$(CONFIG_XBM_PARSER)              += xbm_parser.o
>   OBJS-$(CONFIG_XMA_PARSER)              += xma_parser.o
>   
>   # bitstream filters
> diff --git a/libavcodec/parsers.c b/libavcodec/parsers.c
> index 3156b86b03..93af25ac14 100644
> --- a/libavcodec/parsers.c
> +++ b/libavcodec/parsers.c
> @@ -72,6 +72,7 @@ extern AVCodecParser ff_vp3_parser;
>   extern AVCodecParser ff_vp8_parser;
>   extern AVCodecParser ff_vp9_parser;
>   extern AVCodecParser ff_webp_parser;
> +extern AVCodecParser ff_xbm_parser;
>   extern AVCodecParser ff_xma_parser;
>   
>   #include "libavcodec/parser_list.c"
> diff --git a/libavcodec/xbm_parser.c b/libavcodec/xbm_parser.c
> new file mode 100644
> index 0000000000..30d23200db
> --- /dev/null
> +++ b/libavcodec/xbm_parser.c
> @@ -0,0 +1,101 @@
> +/*
> + * XBM parser
> + * Copyright (c) 2021 Paul B Mahol
> + *
> + * 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
> + */
> +
> +/**
> + * @file
> + * XBM parser
> + */
> +
> +#include "libavutil/common.h"
> +
> +#include "parser.h"
> +
> +typedef struct XBMParseContext {
> +    ParseContext pc;
> +    uint16_t state16;
> +    int count;
> +} XBMParseContext;
> +
> +#define KEY (((uint64_t)'\n' << 56) | ((uint64_t)'#' << 48) | ((uint64_t)'d' << 40) | ((uint64_t)'e' << 32) | ((uint64_t)'f' << 24) | ('i' << 16) | ('n' << 8) | ('e' << 0))

Please split this line.

> +#define END ((';' << 8) | ('\n' << 0))
> +
> +static int xbm_init(AVCodecParserContext *s)
> +{
> +    XBMParseContext *bpc = s->priv_data;
> +
> +    bpc->count = 1;
> +
> +    return 0;
> +}
> +
> +static int xbm_parse(AVCodecParserContext *s, AVCodecContext *avctx,
> +                     const uint8_t **poutbuf, int *poutbuf_size,
> +                     const uint8_t *buf, int buf_size)
> +{
> +    XBMParseContext *bpc = s->priv_data;
> +    uint64_t state = bpc->pc.state64;
> +    uint16_t state16 = bpc->state16;
> +    int next = END_NOT_FOUND, i = 0;
> +
> +    s->pict_type = AV_PICTURE_TYPE_NONE;

The decoder sets every frame to AV_PICTURE_TYPE_I and key_frame = 1, so 
you should do the same here, so the generic lavf code takes it into account.

> +    s->duration  = 1;
> +
> +    *poutbuf_size = 0;
> +    *poutbuf = NULL;
> +
> +    for (; i < buf_size; i++) {
> +        state = (state << 8) | buf[i];
> +        state16 = (state16 << 8) | buf[i];
> +
> +        if (state == KEY)
> +            bpc->count++;
> +
> +        if ((state == KEY && bpc->count == 1)) {
> +            next = i - 6;
> +            break;
> +        } else if (state16 == END) {
> +            next = i + 1;
> +            bpc->count = 0;
> +            break;
> +        }
> +    }
> +
> +    bpc->pc.state64 = state;
> +    bpc->state16 = state16;
> +    if (ff_combine_frame(&bpc->pc, next, &buf, &buf_size) < 0) {
> +        *poutbuf = NULL;
> +        *poutbuf_size = 0;
> +        return buf_size;
> +    }

You could also set s->format and s->width/height if you share some code 
with the decoder (inline within a header preferably) at this point, but 
it's not important.

> +
> +    *poutbuf      = buf;
> +    *poutbuf_size = buf_size;
> +
> +    return next;
> +}
> +
> +AVCodecParser ff_xbm_parser = {
> +    .codec_ids      = { AV_CODEC_ID_XBM },
> +    .priv_data_size = sizeof(XBMParseContext),
> +    .parser_init    = xbm_init,
> +    .parser_parse   = xbm_parse,
> +    .parser_close   = ff_parse_close,
> +};

LGTM if tested otherwise.