[FFmpeg-devel] [PATCH] png parser

[Michael Niedermayer]

On Thu, Jun 04, 2009 at 10:40:55AM +0200, Peter Holik wrote:
> > On Mon, Jun 01, 2009 at 12:27:52PM +0200, Peter Holik wrote:
> >> Hi!
> >>
> >> I've now reworked my patch to really parse a png for end of frame.
> >>
> >> Now you can filter out png's of any stream like
> >>
> >> cat garbage a.png garbage b.png garbage | ffmpeg -f image2pipe -vcodec png -i - c%d.png
> >>
> >> cu Peter
> >>  Makefile     |    1
> >>  allcodecs.c  |    1
> >>  png_parser.c |  124 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >>  3 files changed, 126 insertions(+)
> >> 63f7cd1bb826726f1d2a9e7254410cd7ec98a81c  png-parser.patch
> >> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> >> index 14ef9f4..189231b 100644
> >> --- a/libavcodec/Makefile
> >> +++ b/libavcodec/Makefile
> >> @@ -411,6 +411,7 @@ OBJS-$(CONFIG_MLP_PARSER)              += mlp_parser.o mlp.o
> >>  OBJS-$(CONFIG_MPEG4VIDEO_PARSER)       += mpeg4video_parser.o h263.o mpeg12data.o mpegvideo.o
> >> error_resilience.o
> >>  OBJS-$(CONFIG_MPEGAUDIO_PARSER)        += mpegaudio_parser.o mpegaudiodecheader.o
> >> mpegaudiodata.o
> >>  OBJS-$(CONFIG_MPEGVIDEO_PARSER)        += mpegvideo_parser.o mpeg12.o mpeg12data.o mpegvideo.o
> >> error_resilience.o
> >> +OBJS-$(CONFIG_PNG_PARSER)              += png_parser.o
> >>  OBJS-$(CONFIG_PNM_PARSER)              += pnm_parser.o pnm.o
> >>  OBJS-$(CONFIG_VC1_PARSER)              += vc1_parser.o
> >>  OBJS-$(CONFIG_VP3_PARSER)              += vp3_parser.o
> >> diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
> >> index e8d5d27..362021f 100644
> >> --- a/libavcodec/allcodecs.c
> >> +++ b/libavcodec/allcodecs.c
> >> @@ -334,6 +334,7 @@ void avcodec_register_all(void)
> >>      REGISTER_PARSER  (MPEG4VIDEO, mpeg4video);
> >>      REGISTER_PARSER  (MPEGAUDIO, mpegaudio);
> >>      REGISTER_PARSER  (MPEGVIDEO, mpegvideo);
> >> +    REGISTER_PARSER  (PNG, png);
> >>      REGISTER_PARSER  (PNM, pnm);
> >>      REGISTER_PARSER  (VC1, vc1);
> >>      REGISTER_PARSER  (VP3, vp3);
> >> diff --git a/libavcodec/png_parser.c b/libavcodec/png_parser.c
> >> new file mode 100644
> >> index 0000000..64f2356
> >> --- /dev/null
> >> +++ b/libavcodec/png_parser.c
> >> @@ -0,0 +1,124 @@
> >> +/*
> >> + * PNG parser
> >> + * Copyright (c) 2009 Peter Holik
> >> + *
> >> + * 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 libavcodec/png_parser.c
> >> + * PNG parser
> >> + */
> >> +
> >> +#include "parser.h"
> >> +#include "bytestream.h"
> >> +#include "png.h"
> >> +
> >> +static int png_parse(AVCodecParserContext *s, AVCodecContext *avctx,
> >> +                     const uint8_t **poutbuf, int *poutbuf_size,
> >> +                     const uint8_t *buf, int buf_size)
> >> +{
> >> +    ParseContext *pc = s->priv_data;
> >> +    uint8_t *bytestream;
> >> +    uint8_t *bytestream_start;
> >> +    uint8_t *bytestream_end;
> >> +
> >> +    /* EOF considered as end of frame */
> >> +    if (buf_size == 0)
> >> +        goto flush;
> >> +
> >> +    *poutbuf      = NULL;
> >> +    *poutbuf_size = 0;
> >> +
> >> +    /* first add new buffer to parsebuffer */
> >> +    bytestream_start = av_fast_realloc(pc->buffer, &pc->buffer_size,
> >> +                          pc->index + buf_size + FF_INPUT_BUFFER_PADDING_SIZE);
> >> +    if(!bytestream_start)
> >> +        goto fail;
> >> +    pc->buffer = bytestream_start;
> >> +    memcpy(&pc->buffer[pc->index], buf, buf_size);
> >
> > mandatory copying is unacceptable
> > the case where each input is exactly a png frame for example should
> > be free of any timeconsuming operation
> >
> > maybe ff_combine_frame() would be usefull
> 
> But ff_combine_frame also does memcpy, so there is no difference to my approach.

ff_combine_frame() does not always memcpy, your code does always

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Rewriting code that is poorly written but fully understood is good.
Rewriting code that one doesnt understand is a sign that one is less smart
then the original author, trying to rewrite it will not make it better.
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