Re: [FFmpeg-devel] [PATCH 1/3] lavc/pgs_frame_merge_bsf: add bsf to merge PGS segments

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Andreas Rheinhardt:
> From: John Stebbins <jstebbins@jetheaddev.com>
> 
> Required to remux m2ts to mkv
> Minor changes and porting to FFBitStreamFilter done by the committer.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>  Changelog                        |   1 +
>  doc/bitstream_filters.texi       |   8 ++
>  libavcodec/Makefile              |   1 +
>  libavcodec/bitstream_filters.c   |   1 +
>  libavcodec/pgs_frame_merge_bsf.c | 191 +++++++++++++++++++++++++++++++
>  libavcodec/version.h             |   2 +-
>  6 files changed, 203 insertions(+), 1 deletion(-)
>  create mode 100644 libavcodec/pgs_frame_merge_bsf.c
> 
> diff --git a/Changelog b/Changelog
> index 4d467eb741..1bae64075e 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -14,6 +14,7 @@ version 5.1:
>  - colormap video filter
>  - colorchart video source filter
>  - blurdetect filter
> +- PGS subtitle frame merge bitstream filter
>  
>  
>  version 5.0:
> diff --git a/doc/bitstream_filters.texi b/doc/bitstream_filters.texi
> index fc2c71fc12..50c95f035d 100644
> --- a/doc/bitstream_filters.texi
> +++ b/doc/bitstream_filters.texi
> @@ -695,6 +695,14 @@ for NTSC frame rate using the @option{frame_rate} option.
>  ffmpeg -f lavfi -i sine=r=48000:d=1 -c pcm_s16le -bsf pcm_rechunk=r=30000/1001 -f framecrc -
>  @end example
>  
> +@section pgs_frame_merge
> +
> +Merge a sequence of PGS Subtitle segments ending with an "end of display set"
> +segment into a single packet.
> +
> +This is required by some containers that support PGS subtitles
> +(muxer @code{matroska}).
> +
>  @section prores_metadata
>  
>  Modify color property metadata embedded in prores stream.
> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> index cfaa6f196a..3c0ff2dc58 100644
> --- a/libavcodec/Makefile
> +++ b/libavcodec/Makefile
> @@ -1195,6 +1195,7 @@ OBJS-$(CONFIG_NOISE_BSF)                  += noise_bsf.o
>  OBJS-$(CONFIG_NULL_BSF)                   += null_bsf.o
>  OBJS-$(CONFIG_OPUS_METADATA_BSF)          += opus_metadata_bsf.o
>  OBJS-$(CONFIG_PCM_RECHUNK_BSF)            += pcm_rechunk_bsf.o
> +OBJS-$(CONFIG_PGS_FRAME_MERGE_BSF)        += pgs_frame_merge_bsf.o
>  OBJS-$(CONFIG_PRORES_METADATA_BSF)        += prores_metadata_bsf.o
>  OBJS-$(CONFIG_REMOVE_EXTRADATA_BSF)       += remove_extradata_bsf.o av1_parse.o
>  OBJS-$(CONFIG_SETTS_BSF)                  += setts_bsf.o
> diff --git a/libavcodec/bitstream_filters.c b/libavcodec/bitstream_filters.c
> index f117bc0e17..444423ae93 100644
> --- a/libavcodec/bitstream_filters.c
> +++ b/libavcodec/bitstream_filters.c
> @@ -52,6 +52,7 @@ extern const FFBitStreamFilter ff_noise_bsf;
>  extern const FFBitStreamFilter ff_null_bsf;
>  extern const FFBitStreamFilter ff_opus_metadata_bsf;
>  extern const FFBitStreamFilter ff_pcm_rechunk_bsf;
> +extern const FFBitStreamFilter ff_pgs_frame_merge_bsf;
>  extern const FFBitStreamFilter ff_prores_metadata_bsf;
>  extern const FFBitStreamFilter ff_remove_extradata_bsf;
>  extern const FFBitStreamFilter ff_setts_bsf;
> diff --git a/libavcodec/pgs_frame_merge_bsf.c b/libavcodec/pgs_frame_merge_bsf.c
> new file mode 100644
> index 0000000000..bcd8945335
> --- /dev/null
> +++ b/libavcodec/pgs_frame_merge_bsf.c
> @@ -0,0 +1,191 @@
> +/*
> + * Copyright (c) 2020 John Stebbins <jstebbins.hb@gmail.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
> + */
> +
> +/**
> + * @file
> + * This bitstream filter merges PGS subtitle packets containing incomplete
> + * set of segments into a single packet
> + *
> + * Packets already containing a complete set of segments will be passed through
> + * unchanged.
> + */
> +
> +#include "libavutil/attributes.h"
> +#include "libavutil/intreadwrite.h"
> +#include "libavutil/log.h"
> +#include "bsf.h"
> +#include "bsf_internal.h"
> +
> +enum PGSSegmentType {
> +    PALETTE_SEGMENT         = 0x14,
> +    OBJECT_SEGMENT          = 0x15,
> +    PRESENTATION_SEGMENT    = 0x16,
> +    WINDOW_SEGMENT          = 0x17,
> +    END_DISPLAY_SET_SEGMENT = 0x80,
> +};
> +
> +typedef struct PGSMergeContext {
> +    AVPacket *buffer_pkt, *in;
> +    int presentation_found;
> +    int pkt_flags;
> +} PGSMergeContext;
> +
> +static av_cold void frame_merge_flush(AVBSFContext *bsf)
> +{
> +    PGSMergeContext *ctx = bsf->priv_data;
> +
> +    ctx->presentation_found = ctx->pkt_flags = 0;
> +    av_packet_unref(ctx->in);
> +    av_packet_unref(ctx->buffer_pkt);
> +}
> +
> +static int frame_merge_output(PGSMergeContext *ctx, AVPacket *dst, AVPacket *src)
> +{
> +    if (!ctx->presentation_found)
> +        ctx->pkt_flags |= AV_PKT_FLAG_CORRUPT;
> +    ctx->presentation_found = 0;
> +    src->flags    |= ctx->pkt_flags;
> +    ctx->pkt_flags = 0;
> +    av_packet_move_ref(dst, src);
> +    return 0;
> +}
> +
> +static int frame_merge_filter(AVBSFContext *bsf, AVPacket *out)
> +{
> +    PGSMergeContext *ctx = bsf->priv_data;
> +    AVPacket *in = ctx->in, *pkt = ctx->buffer_pkt;
> +    int ret, size, pos, display = 0, presentation = 0;
> +    unsigned int i;
> +
> +    if (!in->data) {
> +        ret = ff_bsf_get_packet_ref(bsf, in);
> +        if (ret == AVERROR_EOF && pkt->data) {
> +            // Output remaining data
> +            ctx->pkt_flags |= AV_PKT_FLAG_CORRUPT;
> +            return frame_merge_output(ctx, out, pkt);
> +        }
> +        if (ret < 0)
> +            return ret;
> +    }
> +    if (!in->size) {
> +        av_packet_unref(in);
> +        return AVERROR(EAGAIN);
> +    }
> +    in->flags &= ~AV_PKT_FLAG_KEY; // Will be detected in the stream
> +
> +    // Validate packet data and find display_end segment
> +    size = in->size;
> +    i = 0;
> +    while (i + 3 <= in->size) {
> +        uint8_t segment_type = in->data[i];
> +        int     segment_len  = AV_RB16(in->data + i + 1) + 3;
> +
> +        if (i + segment_len > in->size)
> +            break; // Invalid, segments can't span packets
> +        if (segment_type == PRESENTATION_SEGMENT && ctx->presentation_found)
> +            break; // Invalid, there can be only one
> +        if (segment_type == PRESENTATION_SEGMENT) {
> +            uint8_t state;
> +            if (segment_len < 11)
> +                break; // Invalid presentation segment length
> +            ctx->presentation_found = presentation = 1;
> +            state = in->data[i + 10] & 0xc0;
> +            if (state)
> +                ctx->pkt_flags |= AV_PKT_FLAG_KEY;
> +            else
> +                ctx->pkt_flags &= ~AV_PKT_FLAG_KEY;
> +        }
> +        i += segment_len;
> +        if (segment_type == END_DISPLAY_SET_SEGMENT) {
> +            size    = i;
> +            display = 1;
> +            break;
> +        }
> +    }
> +    if (display && pkt->size == 0 && size == in->size) // passthrough
> +        return frame_merge_output(ctx, out, in);
> +    if (!display && i != in->size) {
> +        av_log(bsf, AV_LOG_WARNING, "Failed to parse PGS segments.\n");
> +        // force output what we have
> +        size    = in->size;
> +        display = 1;
> +        ctx->pkt_flags |= AV_PKT_FLAG_CORRUPT;
> +    }
> +
> +    if (presentation) {
> +        ret = av_packet_copy_props(pkt, in);
> +        if (ret < 0)
> +            goto fail;
> +    }
> +    pos = pkt->size;
> +    ret = av_grow_packet(pkt, size);
> +    if (ret < 0)
> +        goto fail;
> +    memcpy(pkt->data + pos, in->data, size);
> +
> +    if (size == in->size)
> +        av_packet_unref(in);
> +    else {
> +        in->data += size;
> +        in->size -= size;
> +    }
> +
> +    if (display)
> +        return frame_merge_output(ctx, out, pkt);
> +    return AVERROR(EAGAIN);
> +
> +fail:
> +    frame_merge_flush(bsf);
> +    return ret;
> +}
> +
> +static av_cold int frame_merge_init(AVBSFContext *bsf)
> +{
> +    PGSMergeContext *ctx = bsf->priv_data;
> +
> +    ctx->in  = av_packet_alloc();
> +    ctx->buffer_pkt = av_packet_alloc();
> +    if (!ctx->in || !ctx->buffer_pkt)
> +        return AVERROR(ENOMEM);
> +
> +    return 0;
> +}
> +
> +static av_cold void frame_merge_close(AVBSFContext *bsf)
> +{
> +    PGSMergeContext *ctx = bsf->priv_data;
> +
> +    av_packet_free(&ctx->in);
> +    av_packet_free(&ctx->buffer_pkt);
> +}
> +
> +static const enum AVCodecID frame_merge_codec_ids[] = {
> +    AV_CODEC_ID_HDMV_PGS_SUBTITLE, AV_CODEC_ID_NONE,
> +};
> +
> +const FFBitStreamFilter ff_pgs_frame_merge_bsf = {
> +    .p.name         = "pgs_frame_merge",
> +    .p.codec_ids    = frame_merge_codec_ids,
> +    .priv_data_size = sizeof(PGSMergeContext),
> +    .init           = frame_merge_init,
> +    .flush          = frame_merge_flush,
> +    .close          = frame_merge_close,
> +    .filter         = frame_merge_filter,
> +};
> diff --git a/libavcodec/version.h b/libavcodec/version.h
> index 735c8b813c..87b7284a95 100644
> --- a/libavcodec/version.h
> +++ b/libavcodec/version.h
> @@ -29,7 +29,7 @@
>  
>  #include "version_major.h"
>  
> -#define LIBAVCODEC_VERSION_MINOR  27
> +#define LIBAVCODEC_VERSION_MINOR  28
>  #define LIBAVCODEC_VERSION_MICRO 100
>  
>  #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \

Will apply this patchset tomorrow unless there are objections.

- Andreas
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