[FFmpeg-devel] [PATCH 2/2] MxPEG decoder

Michael Niedermayer michaelni
Sun Nov 7 14:28:00 CET 2010


On Sat, Nov 06, 2010 at 05:10:41AM +0300, Anatoly Nenashev wrote:
> On 06.11.2010 01:50, Michael Niedermayer wrote:
>> On Fri, Nov 05, 2010 at 09:50:36PM +0300, Anatoly Nenashev wrote:
>>    
>>
>>> +static int mxg_read_packet(AVFormatContext *s, AVPacket *pkt)
>>> +{
>>> +    int ret, size;
>>> +    MXGContext *mxg = s->priv_data;
>>> +
>>> +    while (!url_feof(s->pb)&&  !url_ferror(s->pb)) {
>>> +        uint8_t data = 0;
>>> +        unsigned int current_pad;
>>> +
>>> +        /* search for start marker - 0xff */
>>> +        while (mxg->current_pos + FF_INPUT_BUFFER_PADDING_SIZE<  mxg->buffer_size) {
>>> +            data = get_byte(s->pb);
>>> +            mxg->buffer[mxg->current_pos++] = data;
>>> +            if (data == 0xff) break;
>>> +        }
>>>      
>> you can check 4 bytes at a time with something like:
>> (x&~(x+0x01010101))&  0x80808080
>> this should be faster
>>
>>    
>
> Ok, thanks for your improvements, reimplemented this way. Also marker  
> segment size parsing is added.

>  Makefile     |    1 
>  allformats.c |    1 
>  mxg.c        |  225 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 227 insertions(+)
> 7f1d8269bff394c81c62c3d5b59d47a3cc97032c  mxg_v12.patch
> diff --git a/libavformat/Makefile b/libavformat/Makefile
> index e62a5ea..d3e3cd0 100644
> --- a/libavformat/Makefile
> +++ b/libavformat/Makefile
> @@ -147,6 +147,7 @@ OBJS-$(CONFIG_MTV_DEMUXER)               += mtv.o
>  OBJS-$(CONFIG_MVI_DEMUXER)               += mvi.o
>  OBJS-$(CONFIG_MXF_DEMUXER)               += mxfdec.o mxf.o
>  OBJS-$(CONFIG_MXF_MUXER)                 += mxfenc.o mxf.o audiointerleave.o
> +OBJS-$(CONFIG_MXG_DEMUXER)               += mxg.o
>  OBJS-$(CONFIG_NC_DEMUXER)                += ncdec.o
>  OBJS-$(CONFIG_NSV_DEMUXER)               += nsvdec.o
>  OBJS-$(CONFIG_NULL_MUXER)                += nullenc.o
> diff --git a/libavformat/allformats.c b/libavformat/allformats.c
> index e35f4f8..4afbef5 100644
> --- a/libavformat/allformats.c
> +++ b/libavformat/allformats.c
> @@ -142,6 +142,7 @@ void av_register_all(void)
>      REGISTER_DEMUXER  (MVI, mvi);
>      REGISTER_MUXDEMUX (MXF, mxf);
>      REGISTER_MUXER    (MXF_D10, mxf_d10);
> +    REGISTER_DEMUXER  (MXG, mxg);
>      REGISTER_DEMUXER  (NC, nc);
>      REGISTER_DEMUXER  (NSV, nsv);
>      REGISTER_MUXER    (NULL, null);
> diff --git a/libavformat/mxg.c b/libavformat/mxg.c
> new file mode 100644
> index 0000000..5260086
> --- /dev/null
> +++ b/libavformat/mxg.c
> @@ -0,0 +1,225 @@
> +/*
> + * MxPEG clip file demuxer
> + * Copyright (c) 2010 Anatoly Nenashev
> + *
> + * 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 "libavutil/intreadwrite.h"
> +#include "libavcodec/mjpeg.h"
> +#include "avformat.h"
> +#include "avio.h"
> +
> +#define VIDEO_STREAM_INDEX 0
> +#define AUDIO_STREAM_INDEX 1
> +#define DEFAULT_PACKET_SIZE 1024
> +
> +typedef struct MXGContext {
> +    uint8_t *buffer;
> +    unsigned int buffer_size;
> +    unsigned int current_pos;
> +    int64_t dts;
> +} MXGContext;
> +
> +static int mxg_read_header(AVFormatContext *s, AVFormatParameters *ap)
> +{
> +    AVStream *video_st = 0, *audio_st = 0;
> +    MXGContext *mxg = s->priv_data;
> +
> +    /* video parameters will be extracted from the compressed bitstream */
> +    video_st = av_new_stream(s, VIDEO_STREAM_INDEX);
> +    if (!video_st)
> +        return AVERROR(ENOMEM);
> +    video_st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
> +    video_st->codec->codec_id = CODEC_ID_MXPEG;
> +    av_set_pts_info(video_st, 64, 1, 1000000);
> +
> +    audio_st = av_new_stream(s, AUDIO_STREAM_INDEX);
> +    if (!audio_st)
> +        return AVERROR(ENOMEM);
> +    audio_st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
> +    audio_st->codec->codec_id = CODEC_ID_PCM_ALAW;
> +    audio_st->codec->channels = 1;
> +    audio_st->codec->sample_rate = 8000;
> +    audio_st->codec->bits_per_coded_sample = 8;
> +    audio_st->codec->block_align = 1;
> +    av_set_pts_info(audio_st, 64, 1, 1000000);
> +
> +    mxg->buffer = av_malloc(DEFAULT_PACKET_SIZE);
> +    if (!mxg->buffer)
> +        return AVERROR(ENOMEM);
> +
> +    mxg->buffer_size = DEFAULT_PACKET_SIZE;
> +    mxg->current_pos = 0;
> +    mxg->dts = AV_NOPTS_VALUE;
> +
> +    return 0;
> +}
> +
> +static int mxg_read_packet(AVFormatContext *s, AVPacket *pkt)
> +{
> +    int ret, size;
> +    unsigned int current_pad;
> +    MXGContext *mxg = s->priv_data;
> +
> +    while (!url_feof(s->pb) && !url_ferror(s->pb)) {
> +        uint8_t marker = 0;
> +
> +        /* search for start marker - 0xff */
> +        while (mxg->current_pos + FF_INPUT_BUFFER_PADDING_SIZE < mxg->buffer_size) {
> +            uint32_t x;
> +            uint8_t *p = mxg->buffer + mxg->current_pos;
> +
> +            ret = get_partial_buffer(s->pb, p, 4);

calling this every 4 bytes is slow


> +            if (ret < 0)
> +                return ret;
> +
> +            x = *(uint32_t*)p;
> +            if (x & (~(x+0x01010101)) & 0x80808080) {
> +                if (p[0] == 0xff && ret > 0) {
> +                    mxg->current_pos += 1;
> +                    url_fseek(s->pb, 1 - ret, SEEK_CUR);

these seek back calls can fail

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Dictatorship naturally arises out of democracy, and the most aggravated
form of tyranny and slavery out of the most extreme liberty. -- Plato
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