[FFmpeg-devel] [PATCH 2/6] lavc: split LSCR decoder out of PNG decoder

James Almer jamrial at gmail.com
Sat Feb 20 16:38:42 EET 2021


On 2/16/2021 5:24 PM, Anton Khirnov wrote:
> It shares very little code with pngdec, so keeping them together only
> makes the code harder to read.
> ---
>   libavcodec/Makefile  |   2 +-
>   libavcodec/lscrdec.c | 279 +++++++++++++++++++++++++++++++++++++++++++
>   libavcodec/png.h     |   5 +
>   libavcodec/pngdec.c  | 174 +--------------------------
>   4 files changed, 291 insertions(+), 169 deletions(-)
>   create mode 100644 libavcodec/lscrdec.c
> 
> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> index 3341801b97..b0c6d675d0 100644
> --- a/libavcodec/Makefile
> +++ b/libavcodec/Makefile
> @@ -439,7 +439,7 @@ OBJS-$(CONFIG_KMVC_DECODER)            += kmvc.o
>   OBJS-$(CONFIG_LAGARITH_DECODER)        += lagarith.o lagarithrac.o
>   OBJS-$(CONFIG_LJPEG_ENCODER)           += ljpegenc.o mjpegenc_common.o
>   OBJS-$(CONFIG_LOCO_DECODER)            += loco.o
> -OBJS-$(CONFIG_LSCR_DECODER)            += png.o pngdec.o pngdsp.o
> +OBJS-$(CONFIG_LSCR_DECODER)            += lscrdec.o png.o pngdec.o pngdsp.o
>   OBJS-$(CONFIG_M101_DECODER)            += m101.o
>   OBJS-$(CONFIG_MACE3_DECODER)           += mace.o
>   OBJS-$(CONFIG_MACE6_DECODER)           += mace.o
> diff --git a/libavcodec/lscrdec.c b/libavcodec/lscrdec.c
> new file mode 100644
> index 0000000000..242ae8fcb2
> --- /dev/null
> +++ b/libavcodec/lscrdec.c
> @@ -0,0 +1,279 @@
> +/*
> + * 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 <stdint.h>
> +#include <zlib.h>
> +
> +#include "libavutil/frame.h"
> +#include "libavutil/error.h"
> +#include "libavutil/log.h"
> +
> +#include "avcodec.h"
> +#include "bytestream.h"
> +#include "codec.h"
> +#include "internal.h"
> +#include "packet.h"
> +#include "png.h"
> +#include "pngdsp.h"
> +
> +typedef struct LSCRContext {
> +    PNGDSPContext   dsp;
> +    AVCodecContext *avctx;
> +
> +    AVFrame        *last_picture;
> +    uint8_t        *buffer;
> +    int             buffer_size;
> +    uint8_t        *crow_buf;
> +    int             crow_size;
> +    uint8_t        *last_row;
> +    unsigned int    last_row_size;
> +
> +    GetByteContext  gb;
> +    uint8_t        *image_buf;
> +    int             image_linesize;
> +    int             row_size;
> +    int             cur_h;
> +    int             y;
> +
> +    z_stream        zstream;
> +} LSCRContext;
> +
> +static void handle_row(LSCRContext *s, AVFrame *frame)

Unused frame argument.

> +{
> +    uint8_t *ptr, *last_row;
> +
> +    ptr = s->image_buf + s->image_linesize * s->y;
> +    if (s->y == 0)
> +        last_row = s->last_row;
> +    else
> +        last_row = ptr - s->image_linesize;
> +
> +    ff_png_filter_row(&s->dsp, ptr, s->crow_buf[0], s->crow_buf + 1,
> +                      last_row, s->row_size, 3);
> +
> +    s->y++;
> +}
> +
> +static int decode_idat(LSCRContext *s, AVFrame *frame, int length)
> +{
> +    int ret;
> +    s->zstream.avail_in = FFMIN(length, bytestream2_get_bytes_left(&s->gb));
> +    s->zstream.next_in  = s->gb.buffer;
> +    bytestream2_skip(&s->gb, length);
> +
> +    /* decode one line if possible */
> +    while (s->zstream.avail_in > 0) {
> +        ret = inflate(&s->zstream, Z_PARTIAL_FLUSH);
> +        if (ret != Z_OK && ret != Z_STREAM_END) {
> +            av_log(s->avctx, AV_LOG_ERROR, "inflate returned error %d\n", ret);
> +            return AVERROR_EXTERNAL;
> +        }
> +        if (s->zstream.avail_out == 0) {
> +            if (s->y < s->cur_h) {
> +                handle_row(s, frame);
> +            }
> +            s->zstream.avail_out = s->crow_size;
> +            s->zstream.next_out  = s->crow_buf;
> +        }
> +        if (ret == Z_STREAM_END && s->zstream.avail_in > 0) {
> +            av_log(s->avctx, AV_LOG_WARNING,
> +                   "%d undecompressed bytes left in buffer\n", s->zstream.avail_in);
> +            return 0;
> +        }
> +    }
> +    return 0;
> +}
> +
> +static int decode_frame_lscr(AVCodecContext *avctx,
> +                             void *data, int *got_frame,
> +                             AVPacket *avpkt)
> +{
> +    LSCRContext *const s = avctx->priv_data;
> +    GetByteContext *gb = &s->gb;
> +    AVFrame *frame = data;
> +    int ret, nb_blocks, offset = 0;
> +
> +    if (avpkt->size < 2)
> +        return AVERROR_INVALIDDATA;
> +    if (avpkt->size == 2)
> +        return 0;
> +
> +    bytestream2_init(gb, avpkt->data, avpkt->size);
> +
> +    if ((ret = ff_get_buffer(avctx, frame, AV_GET_BUFFER_FLAG_REF)) < 0)
> +        return ret;
> +
> +    nb_blocks = bytestream2_get_le16(gb);
> +    if (bytestream2_get_bytes_left(gb) < 2 + nb_blocks * (12 + 8))
> +        return AVERROR_INVALIDDATA;
> +
> +    if (s->last_picture->data[0]) {
> +        ret = av_frame_copy(frame, s->last_picture);

You could use ff_reget_buf() instead. And if nb_blocks can be 0 (meaning 
no changes since the previous frame), you could even use the 
FF_REGET_BUFFER_FLAG_READONLY flag and completely avoid any memcpy.


More information about the ffmpeg-devel mailing list