Re: [FFmpeg-devel] [FFmpeg-devel v10 4/9] Added demuxer to handle reading EVC video files

[Michael Niedermayer <michael@niedermayer.cc>]

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On Thu, Aug 25, 2022 at 03:35:12PM +0200, Dawid Kozinski wrote:
> - Provided AVInputFormat structure describing EVC input format (ff_evc_demuxer)
> 
> Signed-off-by: Dawid Kozinski <d.kozinski@samsung.com>
> ---
>  libavformat/Makefile     |   1 +
>  libavformat/allformats.c |   1 +
>  libavformat/evcdec.c     | 142 +++++++++++++++++++++++++++++++++++++++
>  3 files changed, 144 insertions(+)
>  create mode 100644 libavformat/evcdec.c
> 
> diff --git a/libavformat/Makefile b/libavformat/Makefile
> index 7e3f0e6794..a320cac22b 100644
> --- a/libavformat/Makefile
> +++ b/libavformat/Makefile
> @@ -249,6 +249,7 @@ OBJS-$(CONFIG_HCOM_DEMUXER)              += hcom.o pcm.o
>  OBJS-$(CONFIG_HDS_MUXER)                 += hdsenc.o
>  OBJS-$(CONFIG_HEVC_DEMUXER)              += hevcdec.o rawdec.o
>  OBJS-$(CONFIG_HEVC_MUXER)                += rawenc.o
> +OBJS-$(CONFIG_EVC_DEMUXER)               += evcdec.o rawdec.o
>  OBJS-$(CONFIG_EVC_MUXER)                 += rawenc.o
>  OBJS-$(CONFIG_HLS_DEMUXER)               += hls.o hls_sample_encryption.o
>  OBJS-$(CONFIG_HLS_MUXER)                 += hlsenc.o hlsplaylist.o avc.o
> diff --git a/libavformat/allformats.c b/libavformat/allformats.c
> index 31508b69f0..dfce49d149 100644
> --- a/libavformat/allformats.c
> +++ b/libavformat/allformats.c
> @@ -148,6 +148,7 @@ extern const AVInputFormat  ff_ea_cdata_demuxer;
>  extern const AVInputFormat  ff_eac3_demuxer;
>  extern const AVOutputFormat ff_eac3_muxer;
>  extern const AVInputFormat  ff_epaf_demuxer;
> +extern const AVInputFormat  ff_evc_demuxer;
>  extern const AVOutputFormat ff_evc_muxer;
>  extern const AVOutputFormat ff_f4v_muxer;
>  extern const AVInputFormat  ff_ffmetadata_demuxer;
> diff --git a/libavformat/evcdec.c b/libavformat/evcdec.c
> new file mode 100644
> index 0000000000..58dc671d24
> --- /dev/null
> +++ b/libavformat/evcdec.c
> @@ -0,0 +1,142 @@
> +/*
> + * RAW EVC video demuxer
> + *
> + * Copyright (c) 2021 Dawid Kozinski <d.kozinski@samsung.com>
> + *
> + * 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 "libavcodec/get_bits.h"
> +#include "libavcodec/golomb.h"
> +#include "libavcodec/internal.h"
> +
> +#include "rawdec.h"
> +#include "avformat.h"
> +
> +// The length field that indicates the length in bytes of the following NAL unit is configured to be of 4 bytes
> +#define EVC_NAL_UNIT_LENGTH_BYTE        (4)  /* byte */
> +
> +#define EVC_NAL_HEADER_SIZE             (2)  /* byte */
> +#define MAX_SPS_CNT                     (16) /* defined value in EVC standard */
> +
> +// NALU types
> +// @see ISO_IEC_23094-1_2020 7.4.2.2 NAL unit header semantics
> +//
> +#define EVC_NUT_NONIDR                  (0)  /* Coded slice of a non-IDR picture */
> +#define EVC_NUT_IDR                     (1)  /* Coded slice of an IDR picture */
> +#define EVC_NUT_SPS                     (24) /* Sequence parameter set */
> +#define EVC_NUT_PPS                     (25) /* Picture paremeter set */
> +#define EVC_NUT_APS                     (26) /* Adaptation parameter set */
> +#define EVC_NUT_FD                      (27) /* Filler data */
> +#define EVC_NUT_SEI                     (28) /* Supplemental enhancement information */
> +
> +typedef struct EVCParserContext {
> +    int got_sps;
> +    int got_pps;
> +    int got_idr;
> +    int got_nonidr;
> +} EVCParserContext;
> +
> +static int get_nalu_type(const uint8_t *bits, int bits_size)
> +{
> +    int unit_type_plus1 = 0;
> +
> +    if(bits_size >= EVC_NAL_HEADER_SIZE) {
> +        unsigned char *p = (unsigned char *)bits;
> +        // forbidden_zero_bit
> +        if ((p[0] & 0x80) != 0) {
> +            av_log(NULL, AV_LOG_ERROR, "Cannot get bitstream information. Malformed bitstream.\n");
> +            return -1;
> +        }
> +
> +        // nal_unit_type
> +        unit_type_plus1 = (p[0] >> 1) & 0x3F;
> +    }
> +
> +    return unit_type_plus1 - 1;
> +}
> +
> +static uint32_t read_nal_unit_length(const uint8_t *bits, int bits_size)
> +{
> +    uint32_t nalu_len = 0;
> +
> +    if(bits_size >= EVC_NAL_UNIT_LENGTH_BYTE) {
> +
> +        int t = 0;
> +        unsigned char *p = (unsigned char *)bits;
> +
> +        for(int i=0; i<EVC_NAL_UNIT_LENGTH_BYTE; i++) {
> +            t = (t << 8) | p[i];
> +        }
> +
> +        nalu_len = t;
> +        if(nalu_len == 0) {
> +            av_log(NULL, AV_LOG_ERROR, "Invalid bitstream size!\n");
> +            return 0;
> +        }
> +    }
> +
> +    return nalu_len;
> +}
> +
> +static int parse_nal_units(const AVProbeData *p, EVCParserContext *ev)
> +{
> +    int nalu_type;
> +    size_t nalu_size;
> +    unsigned char *bits = (unsigned char *)p->buf;
> +    int bytes_to_read = p->buf_size;
> +
> +    while(bytes_to_read > EVC_NAL_UNIT_LENGTH_BYTE) {
> +
> +        nalu_size = read_nal_unit_length(bits, EVC_NAL_UNIT_LENGTH_BYTE);
> +        if(nalu_size == 0) break;
> +
> +        bits += EVC_NAL_UNIT_LENGTH_BYTE;
> +        bytes_to_read -= EVC_NAL_UNIT_LENGTH_BYTE;
> +
> +        if(bytes_to_read < nalu_size) break;
> +
> +        nalu_type = get_nalu_type(bits, bytes_to_read);
> +
> +        bits += nalu_size;
> +        bytes_to_read -= nalu_size;
> +
> +        if (nalu_type == EVC_NUT_SPS)
> +            ev->got_sps++;
> +        else if (nalu_type == EVC_NUT_PPS)
> +            ev->got_pps++;
> +        else if (nalu_type == EVC_NUT_IDR )
> +            ev->got_idr++;
> +        else if (nalu_type == EVC_NUT_NONIDR)
> +            ev->got_nonidr++;
> +    }
> +
> +    return 0;
> +}
> +

> +static int evc_probe(const AVProbeData *p)
> +{
> +    EVCParserContext ev = {0};
> +    int ret = parse_nal_units(p, &ev);
> +
> +    if (ret == 0 && ev.got_sps && ev.got_pps && (ev.got_idr || ev.got_nonidr > 3))
> +        return AVPROBE_SCORE_EXTENSION + 1;  // 1 more than .mpg
> +
> +    return 0;
> +}

This function is very noisy
Try
make -j32 tools/probetest && tools/probetest 256 4096

there are pages of:
Invalid bitstream size!
Cannot get bitstream information. Malformed bitstream.
Invalid bitstream size!
Invalid bitstream size!

This is a problem because programs must probe their input and
it is not always every format so formats must be silent when data is
not correct during probing

Thanks

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I know you won't believe me, but the highest form of Human Excellence is
to question oneself and others. -- Socrates

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