[FFmpeg-devel] [PATCH] Demuxer for Leitch/Harris' VR native stream format (LXF)
Michael Niedermayer
michaelni
Thu Sep 30 03:13:07 CEST 2010
On Wed, Sep 29, 2010 at 11:43:24AM +0200, Tomas H?rdin wrote:
> On Wed, 2010-09-29 at 11:05 +0200, Stefano Sabatini wrote:
> > On date Wednesday 2010-09-29 09:55:28 +0200, Tomas H?rdin encoded:
> > > On Tue, 2010-09-28 at 19:55 +0200, Michael Niedermayer wrote:
> > > > On Tue, Sep 28, 2010 at 02:59:13PM +0200, Tomas H?rdin wrote:
> > > > [...]
> > > > > +#define LXF_PACKET_HEADER_SIZE 60
> > > > > +#define LXF_HEADER_DATA_SIZE 120
> > > > > +#define LXF_IDENT "LEITCH\0"
> > > > > +#define LXF_IDENT_LENGTH 8
> > > > > +#define LXF_SAMPLERATE 48000
> > > > > +#define LXF_MAX_AUDIO_PACKET (8008*15*4) //15-channel 32-bit NTSC audio frame
> > > > > +
> > > > > +static const AVCodecTag lxf_tags[] = {
> > > > > + { CODEC_ID_MJPEG, 0 },
> > > > > + { CODEC_ID_MPEG1VIDEO, 1 },
> > > > > + { CODEC_ID_MPEG2VIDEO, 2 }, //MpMl, 4:2:0
> > > > > + { CODEC_ID_MPEG2VIDEO, 3 }, //MpPl, 4:2:2
> > > > > + { CODEC_ID_DVVIDEO, 4 }, //DV25
> > > > > + { CODEC_ID_DVVIDEO, 5 }, //DVCPRO
> > > > > + { CODEC_ID_DVVIDEO, 6 }, //DVCPRO50
> > > > > + { CODEC_ID_RAWVIDEO, 7 }, //PIX_FMT_ARGB, where alpha is used for chroma keying
> > > > > + { CODEC_ID_RAWVIDEO, 8 }, //16-bit chroma key
> > > > > + { CODEC_ID_MPEG2VIDEO, 9 }, //4:2:2 CBP ("Constrained Bytes per Gop")
> > > > > + { CODEC_ID_NONE, 0 },
> > > > > +};
> > > > > +
> > > > > +typedef struct {
> > > > > + int channels; //number of audio channels. 0 -> no audio
> > > > > + uint8_t temp[LXF_MAX_AUDIO_PACKET]; //temp buffer for de-planarizing the audio data
> > > > > + int frame_number;
> > > > > +} LXFDemuxContext;
> > > >
> > > > the comments dont look doxygen compatible
> > >
> > > Fixed. doxygen didn't make use of doxyfied comments in lxf_tags, so I
> > > left them as is. Otherwise they get stripped from the code listing. I
> > > also added a comment for frame_number. Updated patch attached.
> > >
> > > /Tomas
> >
> > > diff --git a/Changelog b/Changelog
> > > index a76cec1..13f53a5 100644
> > > --- a/Changelog
> > > +++ b/Changelog
> > > @@ -42,6 +42,7 @@ version <next>:
> > > - make ffprobe accept AVFormatContext options
> > > - yadif filter
> > > - blackframe filter
> > > +- Demuxer for Leitch/Harris' VR native stream format (LXF)
> > >
> > >
> > > version 0.6:
> > > diff --git a/doc/general.texi b/doc/general.texi
> > > index b9953cc..890319b 100644
> >
> > > --- a/doc/general.texi
> > > +++ b/doc/general.texi
> > > @@ -114,6 +114,8 @@ library:
> > > @tab A format used by libvpx
> > > @item LMLM4 @tab @tab X
> > > @tab Used by Linux Media Labs MPEG-4 PCI boards
> > > + at item LXF @tab @tab X
> > > + @tab VR native stream format, used by Leitch/Harris' video servers.
> >
> > Off-topic but this table can be avoided if we find a way to
> > automatically generate it, the description given here may go to a new
> > description field in AVInputFormat (even better: we should have a
> > format ID and have some way to map a name/description to the ID, same
> > for codecs).
>
> I had the same idea today when I was looking at doxygen/documentation.
> Similarly for the -codecs and -formats lists - they should say which
> encoders belong to which decoder (h264 vs libx264, mkv vs webm). But
> yeah, maybe create a separate thread for that.
>
> > > @item Matroska @tab X @tab X
> > > @item Matroska audio @tab X @tab
> > > @item MAXIS XA @tab @tab X
> > > diff --git a/libavformat/Makefile b/libavformat/Makefile
> > > index fb9b176..b3ae72a 100644
> > > --- a/libavformat/Makefile
> > > +++ b/libavformat/Makefile
> > > @@ -105,6 +105,7 @@ OBJS-$(CONFIG_ISS_DEMUXER) += iss.o
> > > OBJS-$(CONFIG_IV8_DEMUXER) += iv8.o
> > > OBJS-$(CONFIG_IVF_DEMUXER) += ivfdec.o riff.o
> > > OBJS-$(CONFIG_LMLM4_DEMUXER) += lmlm4.o
> > > +OBJS-$(CONFIG_LXF_DEMUXER) += lxfdec.o
> > > OBJS-$(CONFIG_M4V_DEMUXER) += m4vdec.o rawdec.o
> > > OBJS-$(CONFIG_M4V_MUXER) += rawenc.o
> > > OBJS-$(CONFIG_MATROSKA_DEMUXER) += matroskadec.o matroska.o \
> > > diff --git a/libavformat/allformats.c b/libavformat/allformats.c
> > > index f9407f0..f9e1fb3 100644
> > > --- a/libavformat/allformats.c
> > > +++ b/libavformat/allformats.c
> > > @@ -110,6 +110,7 @@ void av_register_all(void)
> > > REGISTER_DEMUXER (IV8, iv8);
> > > REGISTER_DEMUXER (IVF, ivf);
> > > REGISTER_DEMUXER (LMLM4, lmlm4);
> > > + REGISTER_DEMUXER (LXF, lxf);
> > > REGISTER_MUXDEMUX (M4V, m4v);
> > > REGISTER_MUXER (MD5, md5);
> > > REGISTER_MUXDEMUX (MATROSKA, matroska);
> > > diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> > > index 0520530..362a056 100644
> > > --- a/libavformat/avformat.h
> > > +++ b/libavformat/avformat.h
> > > @@ -22,8 +22,8 @@
> > > #define AVFORMAT_AVFORMAT_H
> > >
> > > #define LIBAVFORMAT_VERSION_MAJOR 52
> > > -#define LIBAVFORMAT_VERSION_MINOR 78
> > > -#define LIBAVFORMAT_VERSION_MICRO 5
> > > +#define LIBAVFORMAT_VERSION_MINOR 79
> > > +#define LIBAVFORMAT_VERSION_MICRO 0
> > >
> > > #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
> > > LIBAVFORMAT_VERSION_MINOR, \
> > > diff --git a/libavformat/lxfdec.c b/libavformat/lxfdec.c
> > > new file mode 100644
> > > index 0000000..900f55e
> > > --- /dev/null
> > > +++ b/libavformat/lxfdec.c
> > > @@ -0,0 +1,354 @@
> > > +/*
> > > + * LXF demuxer
> > > + * Copyright (c) 2010 Tomas H?rdin
> > > + *
> > > + * 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 "avformat.h"
> > > +#include "riff.h"
> > > +
> > > +#define LXF_PACKET_HEADER_SIZE 60
> > > +#define LXF_HEADER_DATA_SIZE 120
> > > +#define LXF_IDENT "LEITCH\0"
> > > +#define LXF_IDENT_LENGTH 8
> > > +#define LXF_SAMPLERATE 48000
> > > +#define LXF_MAX_AUDIO_PACKET (8008*15*4) ///< 15-channel 32-bit NTSC audio frame
> > > +
> > > +static const AVCodecTag lxf_tags[] = {
> > > + { CODEC_ID_MJPEG, 0 },
> > > + { CODEC_ID_MPEG1VIDEO, 1 },
> > > + { CODEC_ID_MPEG2VIDEO, 2 }, //MpMl, 4:2:0
> > > + { CODEC_ID_MPEG2VIDEO, 3 }, //MpPl, 4:2:2
> > > + { CODEC_ID_DVVIDEO, 4 }, //DV25
> > > + { CODEC_ID_DVVIDEO, 5 }, //DVCPRO
> > > + { CODEC_ID_DVVIDEO, 6 }, //DVCPRO50
> > > + { CODEC_ID_RAWVIDEO, 7 }, //PIX_FMT_ARGB, where alpha is used for chroma keying
> > > + { CODEC_ID_RAWVIDEO, 8 }, //16-bit chroma key
> > > + { CODEC_ID_MPEG2VIDEO, 9 }, //4:2:2 CBP ("Constrained Bytes per Gop")
> > > + { CODEC_ID_NONE, 0 },
> > > +};
> > > +
> > > +typedef struct {
> > > + int channels; ///< number of audio channels. zero means no audio
> > > + uint8_t temp[LXF_MAX_AUDIO_PACKET]; ///< temp buffer for de-planarizing the audio data
> > > + int frame_number; ///< current video frame
> > > +} LXFDemuxContext;
> > > +
> > > +static int lxf_probe(AVProbeData *p)
> > > +{
> > > + if (!memcmp(p->buf, LXF_IDENT, LXF_IDENT_LENGTH))
> > > + return AVPROBE_SCORE_MAX;
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +/**
> > > + * Verify the checksum of an LXF packet header
> > > + *
> > > + * @param[in] header the packet header to check
> > > + * @return zero if the checksum is OK, non-zero otherwise
> > > + */
> > > +static int check_checksum(const uint8_t *header)
> > > +{
> > > + int x;
> > > + uint32_t sum = 0;
> > > +
> > > + for (x = 0; x < LXF_PACKET_HEADER_SIZE; x += 4)
> > > + sum += AV_RL32(&header[x]);
> > > +
> > > + return sum;
> > > +}
> > > +
> > > +/**
> > > + * Read input until we find the next ident. If found, copy it to the header buffer
> > > + *
> > > + * @param[out] header where to copy the ident to
> > > + * @return 0 if an ident was found, < 0 on I/O error
> > > + */
> > > +static int sync(AVFormatContext *s, uint8_t *header)
> > > +{
> > > + uint8_t buf[LXF_IDENT_LENGTH];
> > > +
> > > + if (get_buffer(s->pb, buf, LXF_IDENT_LENGTH) < 0)
> > > + return AVERROR_IO;
> > > +
> > > + while (memcmp(buf, LXF_IDENT, LXF_IDENT_LENGTH)) {
> > > + if (url_feof(s->pb))
> > > + return AVERROR_EOF;
> > > +
> > > + memmove(buf, &buf[1], LXF_IDENT_LENGTH-1);
> > > + buf[LXF_IDENT_LENGTH-1] = get_byte(s->pb);
> > > + }
> > > +
> > > + memcpy(header, LXF_IDENT, LXF_IDENT_LENGTH);
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +/**
> > > + * Read and checksum the next packet header
> > > + *
> > > + * @param[out] header the read packet header
> > > + * @param[out] format context dependent format information
> > > + * @return the size of the payload following the header or < 0 on failure
> > > + */
> > > +static int get_packet_header(AVFormatContext *s, uint8_t *header, uint32_t *format)
> > > +{
> > > + ByteIOContext *pb = s->pb;
> > > + int track_size, samples, ret;
> > > + AVStream *st;
> > > +
> > > + //find and read the ident
> > > + if ((ret = sync(s, header)) < 0)
> > > + return ret;
> > > +
> > > + //read the rest of the packet header
> > > + if ((ret = get_buffer(pb, header + LXF_IDENT_LENGTH,
> > > + LXF_PACKET_HEADER_SIZE - LXF_IDENT_LENGTH)) !=
> > > + LXF_PACKET_HEADER_SIZE - LXF_IDENT_LENGTH)
> > > + return ret;
> > > +
> > > + if (check_checksum(header))
> > > + av_log(s, AV_LOG_ERROR, "checksum error\n");
> > > +
> > > + *format = AV_RL32(&header[32]);
> > > + ret = AV_RL32(&header[36]);
> > > +
> > > + //type
> > > + switch (AV_RL32(&header[16])) {
> > > + case 0:
> > > + //video
> > > + //skip VBI data and metadata
> > > + url_fskip(pb, (int64_t)(uint32_t)AV_RL32(&header[44]) +
> > > + (int64_t)(uint32_t)AV_RL32(&header[52]));
> > > + break;
> > > + case 1:
> > > + //audio
> > > + if (!(st = s->streams[1])) {
> > > + av_log(s, AV_LOG_INFO, "got audio packet, but no audio stream present\n");
> > > + break;
> > > + }
> > > +
> > > + //set codec based on specified audio bitdepth
> > > + //we only support tightly packed 16-, 20-, 24- and 32-bit PCM at the moment
> > > + *format = AV_RL32(&header[40]);
> > > + st->codec->bits_per_coded_sample = (*format >> 6) & 0x3F;
> > > +
> > > + if (st->codec->bits_per_coded_sample != (*format & 0x3F)) {
> > > + av_log(s, AV_LOG_WARNING, "only tightly packed PCM currently supported\n");
> > > + return AVERROR_PATCHWELCOME;
> > > + }
> > > +
> >
> > > + switch (st->codec->bits_per_coded_sample) {
> > > + case 16:
> > > + st->codec->codec_id = CODEC_ID_PCM_S16LE;
> > > + break;
> > > + case 20:
> > > + st->codec->codec_id = CODEC_ID_PCM_LXF;
> > > + break;
> > > + case 24:
> > > + st->codec->codec_id = CODEC_ID_PCM_S24LE;
> > > + break;
> > > + case 32:
> > > + st->codec->codec_id = CODEC_ID_PCM_S32LE;
> > > + break;
> >
> > This can be:
> > case X: st->codec->codec_id = CODEC_ID_PCM_Y; break;
> >
> > for better alignment / readability.
>
> Good idea. Fixed.
>
> > > + default:
> > > + av_log(s, AV_LOG_WARNING,
> > > + "only 16-, 20-, 24- and 32-bit PCM currently supported\n");
> > > + return AVERROR_PATCHWELCOME;
> > > + }
> > > +
> > > + track_size = AV_RL32(&header[48]);
> > > + samples = track_size * 8 / st->codec->bits_per_coded_sample;
> > > +
> > > + //use audio packet size to determine video standard
> > > + //for NTSC we have one 8008-sample audio frame per five video frames
> > > + if (samples == LXF_SAMPLERATE * 5005 / 30000) {
> > > + av_set_pts_info(s->streams[0], 64, 1001, 30000);
> > > + } else {
> > > + //assume PAL, but warn if we don't have 1920 samples
> > > + if (samples != LXF_SAMPLERATE / 25)
> > > + av_log(s, AV_LOG_WARNING,
> > > + "video doesn't seem to be PAL or NTSC. guessing PAL\n");
> > > +
> > > + av_set_pts_info(s->streams[0], 64, 1, 25);
> > > + }
> > > +
> > > + //TODO: warning if track mask != (1 << channels) - 1?
> > > + ret = av_popcount(AV_RL32(&header[44])) * track_size;
> > > +
> > > + break;
> > > + default:
> > > + break;
> > > + }
> > > +
> > > + return ret;
> > > +}
> > > +
> > > +static int lxf_read_header(AVFormatContext *s, AVFormatParameters *ap)
> > > +{
> > > + LXFDemuxContext *lxf = s->priv_data;
> > > + ByteIOContext *pb = s->pb;
> > > + uint8_t header[LXF_PACKET_HEADER_SIZE], header_data[LXF_HEADER_DATA_SIZE];
> > > + int ret;
> > > + AVStream *st;
> > > + uint32_t format, video_params, disk_params;
> > > + uint16_t record_date, expiration_date;
> > > +
> > > + if ((ret = get_packet_header(s, header, &format)) < 0)
> > > + return ret;
> > > +
> > > + if (ret != LXF_HEADER_DATA_SIZE) {
> > > + av_log(s, AV_LOG_ERROR, "expected %d B size header, got %d\n",
> > > + LXF_HEADER_DATA_SIZE, ret);
> > > + return -1;
> >
> > AVERROR_INVALIDDATA
>
> Fixed.
>
> > > + }
> > > +
> > > + if (get_buffer(pb, header_data, LXF_HEADER_DATA_SIZE) != LXF_HEADER_DATA_SIZE)
> > > + return AVERROR_IO;
> > > +
> > > + if (!(st = av_new_stream(s, 0)))
> > > + return AVERROR_NOMEM;
> > > +
> > > + st->duration = AV_RL32(&header_data[32]);
> > > + video_params = AV_RL32(&header_data[40]);
> > > + record_date = AV_RL16(&header_data[56]);
> > > + expiration_date = AV_RL16(&header_data[58]);
> > > + disk_params = AV_RL32(&header_data[116]);
> > > +
> > > + st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
> > > + st->codec->bit_rate = 1000000 * ((video_params >> 14) & 0xFF);
> > > + st->codec->codec_tag = video_params & 0xF;
> > > + st->codec->codec_id = ff_codec_get_id(lxf_tags, st->codec->codec_tag);
> > > +
> > > + av_log(s, AV_LOG_DEBUG, "record: %x = %i-%02i-%02i\n",
> > > + record_date, 1900 + (record_date & 0x7F), (record_date >> 7) & 0xF,
> > > + (record_date >> 11) & 0x1F);
> > > +
> > > + av_log(s, AV_LOG_DEBUG, "expire: %x = %i-%02i-%02i\n",
> > > + expiration_date, 1900 + (expiration_date & 0x7F), (expiration_date >> 7) & 0xF,
> > > + (expiration_date >> 11) & 0x1F);
> > > +
> > > + if ((video_params >> 22) & 1)
> > > + av_log(s, AV_LOG_WARNING, "VBI data not yet supported\n");
> > > +
> > > + if ((lxf->channels = (disk_params >> 2) & 0xF)) {
> > > + if (!(st = av_new_stream(s, 1)))
> > > + return AVERROR_NOMEM;
> > > +
> > > + st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
> > > + st->codec->sample_rate = LXF_SAMPLERATE;
> > > + st->codec->channels = lxf->channels;
> > > +
> > > + av_set_pts_info(st, 64, 1, st->codec->sample_rate);
> > > + }
> > > +
> > > + if (format == 1) {
> > > + //skip extended field data
> > > + url_fskip(s->pb, (uint32_t)AV_RL32(&header[40]));
> > > + }
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +/**
> > > + * De-planerize the PCM data in lxf->temp
> > > + * FIXME: remove this once support for planar audio is added to libavcodec
> > > + *
> > > + * @param[out] out where to write the de-planerized data to
> > > + * @param[in] bytes the total size of the PCM data
> > > + */
> > > +static void deplanarize(LXFDemuxContext *lxf, AVStream *ast, uint8_t *out, int bytes)
> > > +{
> > > + int x, y, z, i, bytes_per_sample = ast->codec->bits_per_coded_sample >> 3;
> > > +
> > > + for (z = i = 0; z < lxf->channels; z++)
> > > + for (y = 0; y < bytes / bytes_per_sample / lxf->channels; y++)
> > > + for (x = 0; x < bytes_per_sample; x++, i++)
> > > + out[x + bytes_per_sample*(z + y*lxf->channels)] = lxf->temp[i];
> > > +}
> > > +
> > > +static int lxf_read_packet(AVFormatContext *s, AVPacket *pkt)
> > > +{
> > > + LXFDemuxContext *lxf = s->priv_data;
> > > + ByteIOContext *pb = s->pb;
> > > + uint8_t header[LXF_PACKET_HEADER_SIZE], *buf;
> > > + AVStream *ast = NULL;
> > > + uint32_t stream, format;
> > > + int ret;
> > > +
> > > + if ((ret = get_packet_header(s, header, &format)) < 0)
> > > + return ret;
> > > +
> > > + stream = AV_RL32(&header[16]);
> > > +
> > > + if (stream > 1) {
> > > + av_log(s, AV_LOG_WARNING, "got packet with illegal stream index %u\n", stream);
> > > + return AVERROR(EAGAIN);
> > > + }
> > > +
> >
> > > + if (stream == 1 && !(ast = s->streams[1])) {
> > > + av_log(s, AV_LOG_ERROR, "got audio packet without having an audio stream\n");
> > > + return -1;
> > > + }
> >
> > AVERROR_INVALIDDATA
>
> Fixed.
>
> > > +
> > > + //make sure the data fits in the de-planerization buffer
> > > + if (ast && ret > LXF_MAX_AUDIO_PACKET) {
> > > + av_log(s, AV_LOG_ERROR, "audio packet too large (%i > %i)\n",
> > > + ret, LXF_MAX_AUDIO_PACKET);
> > > + return -1;
> > > + }
> >
> > ditto
>
> Fixed.
>
> > > + if (av_new_packet(pkt, ret))
> > > + return AVERROR_IO;
> >
> > maybe you can propagate the error given by av_new_packet()
>
> Fixed.
>
> I also did similar things in various places. For instance, I made all
> places where get_buffer() is used return either the error (if return <
> 0) or AVERROR_EOF (if we didn't get the expected amount of data).
>
> > > +
> > > + //read non-20-bit audio data into lxf->temp so we can deplanarize it
> > > + buf = ast && ast->codec->codec_id != CODEC_ID_PCM_LXF ? lxf->temp : pkt->data;
> > > +
> > > + if (get_buffer(pb, buf, ret) != ret) {
> > > + av_free_packet(pkt);
> > > + return AVERROR_IO;
> > > + }
> > > +
> > > + pkt->stream_index = stream;
> > > +
> > > + if (ast) {
> > > + if(ast->codec->codec_id != CODEC_ID_PCM_LXF)
> > > + deplanarize(lxf, ast, pkt->data, ret);
> > > + } else {
> > > + //picture type (0 = closed I, 1 = open I, 2 = P, 3 = B)
> > > + if (((format >> 22) & 0x3) < 2)
> > > + pkt->flags |= AV_PKT_FLAG_KEY;
> > > +
> > > + pkt->dts = lxf->frame_number++;
> > > + }
> > > +
> > > + return ret;
> > > +}
> > > +
> >
> > > +AVInputFormat lxf_demuxer = {
> > > + "lxf",
> > > + NULL_IF_CONFIG_SMALL("VR native stream format (LXF)"),
> > > + sizeof(LXFDemuxContext),
> > > + lxf_probe,
> > > + lxf_read_header,
> > > + lxf_read_packet,
> > > + .codec_tag = (const AVCodecTag* const []){lxf_tags, 0},
> > > +};
> >
> > possibly use designated init, more readable and doesn't break when we
> > break ABI
>
> Fixed. I used the names for all of them. New patch attached.
>
> /Tomas
> Changelog | 1
> doc/general.texi | 2
> libavformat/Makefile | 1
> libavformat/allformats.c | 1
> libavformat/avformat.h | 4
> libavformat/lxfdec.c | 348 +++++++++++++++++++++++++++++++++++++++++++++++
> 6 files changed, 355 insertions(+), 2 deletions(-)
> 0b6b79313d73797579fab0a8b076a59ccfea8a98 lxfdec9.patch
should be ok
seeking could also be implemented ...
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Old school: Use the lowest level language in which you can solve the problem
conveniently.
New school: Use the highest level language in which the latest supercomputer
can solve the problem without the user falling asleep waiting.
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