[FFmpeg-devel] [PATCH 1/4] lavc/pgs_frame_merge_bsf: add bsf to merge PGS segments
Andreas Rheinhardt
andreas.rheinhardt at gmail.com
Sat May 2 23:30:42 EEST 2020
John Stebbins:
> Required to remux m2ts to mkv
> ---
> Changelog | 1 +
> doc/bitstream_filters.texi | 8 ++
> libavcodec/Makefile | 1 +
> libavcodec/bitstream_filters.c | 1 +
> libavcodec/pgs_frame_merge_bsf.c | 168 +++++++++++++++++++++++++++++++
> 5 files changed, 179 insertions(+)
> create mode 100644 libavcodec/pgs_frame_merge_bsf.c
>
> diff --git a/Changelog b/Changelog
> index d9fcd8bb0a..fec4867488 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -59,6 +59,7 @@ version <next>:
> - mv30 decoder
> - Expanded styling support for 3GPP Timed Text Subtitles (movtext)
> - WebP parser
> +- PGS subtitle frame merge bitstream filter
>
>
> version 4.2:
> diff --git a/doc/bitstream_filters.texi b/doc/bitstream_filters.texi
> index 8fe5b3ad75..21ed09986c 100644
> --- a/doc/bitstream_filters.texi
> +++ b/doc/bitstream_filters.texi
> @@ -548,6 +548,14 @@ ffmpeg -i INPUT -c copy -bsf noise[=1] output.mkv
> @section null
> This bitstream filter passes the packets through unchanged.
>
> + at 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 88944d9a3a..b630de21bc 100644
> --- a/libavcodec/Makefile
> +++ b/libavcodec/Makefile
> @@ -1115,6 +1115,7 @@ OBJS-$(CONFIG_MP3_HEADER_DECOMPRESS_BSF) += mp3_header_decompress_bsf.o \
> OBJS-$(CONFIG_MPEG2_METADATA_BSF) += mpeg2_metadata_bsf.o
> OBJS-$(CONFIG_NOISE_BSF) += noise_bsf.o
> OBJS-$(CONFIG_NULL_BSF) += null_bsf.o
> +OBJS-$(CONFIG_PGS_FRAME_MERGE_BSF) += pgs_frame_merge_bsf.o
> OBJS-$(CONFIG_PRORES_METADATA_BSF) += prores_metadata_bsf.o
> OBJS-$(CONFIG_REMOVE_EXTRADATA_BSF) += remove_extradata_bsf.o
> OBJS-$(CONFIG_TEXT2MOVSUB_BSF) += movsub_bsf.o
> diff --git a/libavcodec/bitstream_filters.c b/libavcodec/bitstream_filters.c
> index 6b5ffe4d70..92619225f0 100644
> --- a/libavcodec/bitstream_filters.c
> +++ b/libavcodec/bitstream_filters.c
> @@ -49,6 +49,7 @@ extern const AVBitStreamFilter ff_mpeg4_unpack_bframes_bsf;
> extern const AVBitStreamFilter ff_mov2textsub_bsf;
> extern const AVBitStreamFilter ff_noise_bsf;
> extern const AVBitStreamFilter ff_null_bsf;
> +extern const AVBitStreamFilter ff_pgs_frame_merge_bsf;
> extern const AVBitStreamFilter ff_prores_metadata_bsf;
> extern const AVBitStreamFilter ff_remove_extradata_bsf;
> extern const AVBitStreamFilter ff_text2movsub_bsf;
> diff --git a/libavcodec/pgs_frame_merge_bsf.c b/libavcodec/pgs_frame_merge_bsf.c
> new file mode 100644
> index 0000000000..cae5c75655
> --- /dev/null
> +++ b/libavcodec/pgs_frame_merge_bsf.c
> @@ -0,0 +1,168 @@
> +/*
> + * Copyright (c) 2020 John Stebbins <jstebbins.hb at 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 "avcodec.h"
> +#include "bsf.h"
> +#include "libavutil/intreadwrite.h"
> +
> +enum PGSSegmentType {
> + PALETTE_SEGMENT = 0x14,
> + OBJECT_SEGMENT = 0x15,
> + PRESENTATION_SEGMENT = 0x16,
> + WINDOW_SEGMENT = 0x17,
> + DISPLAY_SEGMENT = 0x80,
> +};
> +
> +typedef struct PGSMergeContext {
> + AVPacket *buffer_pkt, *in;
> + int presentation_found;
> +} PGSMergeContext;
> +
> +static void frame_merge_flush(AVBSFContext *bsf)
> +{
> + PGSMergeContext *ctx = bsf->priv_data;
> +
> + av_packet_unref(ctx->in);
> + av_packet_unref(ctx->buffer_pkt);
flush should reset ctx->presentation_found, shouldn't it?
> +}
> +
> +static int frame_merge_filter(AVBSFContext *bsf, AVPacket *out)
> +{
> + PGSMergeContext *ctx = bsf->priv_data;
> + AVPacket *in = ctx->in, *pkt = ctx->buffer_pkt;
> + int ret, i, size, pos, display = 0;
> +
> + if (!in->data) {
> + ret = ff_bsf_get_packet_ref(bsf, in);
> + if (ret < 0)
> + return ret;
> + }
> + if (!in->size) {
> + av_packet_unref(in);
> + return AVERROR(EAGAIN);
> + }
> +
> + // Validate packet data and find display_end segment
> + size = in->size;
> + i = 0;
> + while (i + 3 <= in->size) {
> + uint8_t segment_type;
> + int segment_len;
> +
> + segment_type = in->data[i];
> + segment_len = AV_RB16(in->data + i + 1) + 3;
> + if (i + segment_len > in->size) // Invalid data
Possible overflow. Use an unsigned as segment_len to avoid it.
> + break;
> + if (segment_type == PRESENTATION_SEGMENT && i + 10 < in->size &&
> + !ctx->presentation_found) {
> + uint8_t state;
> + ctx->presentation_found = 1;
> + ret = av_packet_copy_props(pkt, in);
This will copy the properties even if it eventually turns out that one
can just pass through the packet. Even worse: Imagine the input packet
having side-data. Then pkt contains side-data, yet the code thinks that
this packet is blank. This side data will then leak when the properties
of the next presentation segment are copied.
Furthermore, I would actually have expected the pts of the display
segment to be used. Or are they guaranteed to be identical?
> + if (ret < 0)
> + goto fail;
> + state = in->data[i + 10] & 0xc0;
This amounts to the composition_state of the composition_descriptor(),
doesn't it?
> + if (state)
> + pkt->flags |= AV_PKT_FLAG_KEY;
The keyframe flag will be ignored on passthrough. Also, should the flag
be cleared if state == 0?
> + }
> + i += segment_len;
> + if (segment_type == DISPLAY_SEGMENT) {
> + size = display = i;
> + break;
> + }
> + }
> + if (display && pkt->size == 0 && size == in->size) { // passthrough
> + ctx->presentation_found = 0;
> + av_packet_move_ref(out, in);
> + return 0;
> + }
> + if ((!display && i != in->size) || size > in->size) {
I don't see how size > in->size can ever be true.
> + av_log(bsf, AV_LOG_WARNING, "Failed to parse PGS segments.\n");
> + // force output what we have
> + display = size = in->size;
If you output a corrupt packet, you should set the AV_PKT_FLAG_CORRUPT flag.
> + }
> +
> + 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) {
> + ctx->presentation_found = 0;
I don't see anything in the code that actually enforces that a
presentation segment has been found at this point; the properties of the
output packet would then still be blank. Is this intended? If it is
spec-incompliant, then one should add the AV_PKT_FLAG_CORRUPT flag.
> + av_packet_move_ref(out, pkt);
> + return 0;
> + }
> + return AVERROR(EAGAIN);
> +
> +fail:
> + ctx->presentation_found = 0;
> + frame_merge_flush(bsf);
> + return ret;
> +}
> +
> +static 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 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 AVBitStreamFilter ff_pgs_frame_merge_bsf = {
> + .name = "pgs_frame_merge",
> + .priv_data_size = sizeof(PGSMergeContext),
> + .init = frame_merge_init,
> + .flush = frame_merge_flush,
> + .close = frame_merge_close,
> + .filter = frame_merge_filter,
> + .codec_ids = frame_merge_codec_ids,
> +};
>
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