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Date: Fri, 29 May 2026 07:57:43 +0900
To: "cygwin@cygwin.com" <cygwin@cygwin.com>
Subject: Re: "Invalid DTS" warnings only in Cygwin version of ffmpeg
Message-Id: <20260529075743.9c2466366921f6171f280ef9@nifty.ne.jp>
In-Reply-To: <PR3PR09MB433011445CBFA2C376E5ECACB0082@PR3PR09MB4330.eurprd09.prod.outlook.com>
References: <PR3PR09MB433011445CBFA2C376E5ECACB0082@PR3PR09MB4330.eurprd09.prod.outlook.com>
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From: Takashi Yano via Cygwin <cygwin@cygwin.com>
Reply-To: Takashi Yano <takashi.yano@nifty.ne.jp>
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Hi destal,

On Wed, 27 May 2026 06:20:36 +0000
destal takul wrote:
> Thank you for the clarification. Is there any way to fix the files that were remuxed with those warnings, or do I have to remux from the original? I have been using the Cygwin version of ffmpeg to cut the end of videos muxed with mkvmerge on non-key-frames since mkvmerge itself doesn't support this, and I probably have hundreds of files that have been remuxed with such warnings over the course of the past few years.

Sorry for inconvinience.
Could you please try attached tool? This should fix the broken
timestamp.

Usage: fix_ts broken.mkv output.mkv

To compile this, you need libavformat-devel, libavcodec-devel,
and libavutil-deve packages.

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>

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#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
	int index;
	int display_rank;
} FrameMap;

static int cmp_frame(const void *a, const void *b) {
	return ((FrameMap*)a)->display_rank - ((FrameMap*)b)->display_rank;
}

#define MAX_REORDER_DELAY 16

void cleanup(AVFormatContext *ifmt, AVFormatContext *ofmt,
		AVCodecParserContext *parser, AVCodecContext *codec_ctx,
		FrameMap *map, FrameMap *sorted) {
	if (parser) av_parser_close(parser);
	if (codec_ctx) avcodec_free_context(&codec_ctx);
	if (ifmt) avformat_close_input(&ifmt);
	if (ofmt) {
		if (!(ofmt->oformat->flags & AVFMT_NOFILE)) avio_closep(&ofmt->pb);
		avformat_free_context(ofmt);
	}
	if (map) free(map);
	if (sorted) free(sorted);
}

int main(int argc, char **argv) {
	int ret = 1;
	if (argc < 3) {
		fprintf(stderr, "Usage: %s in.mkv out.mkv\n", argv[0]);
		return 1;
	}

	AVFormatContext *ifmt = NULL, *ofmt = NULL;
	AVCodecParserContext *parser = NULL;
	AVCodecContext *codec_ctx = NULL;
	FrameMap *map = NULL, *sorted = NULL;
	int frame_count = 0, frame_cap = 10000;

	if (avformat_open_input(&ifmt, argv[1], NULL, NULL) < 0) {
		fprintf(stderr, "avformat_open_input() failed.\n");
		goto end;
	}
	if (avformat_find_stream_info(ifmt, NULL) < 0) {
		fprintf(stderr, "avformat_find_stream_info() failed.\n");
		goto end;
	}

	int video_index = -1;
	for (unsigned i = 0; i < ifmt->nb_streams; i++)
		if (ifmt->streams[i]->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
			video_index = i;

	parser = av_parser_init(AV_CODEC_ID_H264);
	codec_ctx = avcodec_alloc_context3(NULL);
	avcodec_parameters_to_context(codec_ctx,
			ifmt->streams[video_index]->codecpar);

	map = malloc(frame_cap * sizeof(FrameMap));
	AVPacket pkt;
	uint64_t pict_num_msb = 0;
	int prev_pict_num = -1;

	while (av_read_frame(ifmt, &pkt) >= 0) {
		if (pkt.stream_index == video_index) {
			if (frame_count >= frame_cap) {
				frame_cap *= 2;
				map = realloc(map, frame_cap * sizeof(FrameMap));
			}
			uint8_t *data; int size;
			av_parser_parse2(parser, codec_ctx, &data, &size,
					pkt.data, pkt.size, AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
			if (prev_pict_num >= 0 &&
					parser->output_picture_number - prev_pict_num
					< -MAX_REORDER_DELAY)
				pict_num_msb++;
			map[frame_count] =
				(FrameMap){frame_count, parser->output_picture_number
					+ (int)(pict_num_msb * 1024)};
			prev_pict_num = parser->output_picture_number;
			frame_count++;
		}
		av_packet_unref(&pkt);
	}

	sorted = malloc(frame_count * sizeof(FrameMap));
	memcpy(sorted, map, frame_count * sizeof(FrameMap));
	qsort(sorted, frame_count, sizeof(FrameMap), cmp_frame);
	for (int i = 0; i < frame_count; i++)
		map[sorted[i].index].display_rank = i;

	if (avformat_alloc_output_context2(&ofmt, NULL, NULL, argv[2]) != 0) {
		fprintf(stderr, "avformat_alloc_output_context2() failed.\n");
		goto end;
	}
	for (unsigned i = 0; i < ifmt->nb_streams; i++) {
		AVStream *out_st = avformat_new_stream(ofmt, NULL);
		avcodec_parameters_copy(out_st->codecpar, ifmt->streams[i]->codecpar);
	}

	AVStream *in_st = ifmt->streams[video_index];

	if (!(ofmt->oformat->flags & AVFMT_NOFILE))
		avio_open(&ofmt->pb, argv[2], AVIO_FLAG_WRITE);
	if (avformat_write_header(ofmt, NULL) < 0) {
		fprintf(stderr, "avformat_write_header() failed.\n");
		goto end;
	}

	AVRational out_tb = ofmt->streams[video_index]->time_base;

	AVRational frame_rate = in_st->avg_frame_rate;
	if (frame_rate.num == 0)
		frame_rate = in_st->r_frame_rate;

	av_seek_frame(ifmt, video_index, 0, AVSEEK_FLAG_BACKWARD);
	int current = 0;
	while (av_read_frame(ifmt, &pkt) >= 0) {
		if (pkt.stream_index == video_index) {
			pkt.pts = av_rescale_q(map[current].display_rank,
					av_inv_q(frame_rate), out_tb);
			pkt.dts = av_rescale_q(current - MAX_REORDER_DELAY,
					av_inv_q(frame_rate), out_tb);
			pkt.duration = av_rescale_q(1, av_inv_q(frame_rate), out_tb);
			current++;
		}
		if (ifmt->streams[pkt.stream_index]->codecpar->codec_type
				== AVMEDIA_TYPE_AUDIO)
			av_packet_rescale_ts(&pkt,
					ifmt->streams[pkt.stream_index]->time_base,
					ofmt->streams[pkt.stream_index]->time_base);
		av_interleaved_write_frame(ofmt, &pkt);
		av_packet_unref(&pkt);
	}
	av_write_trailer(ofmt);
	ret = 0;

end:
	cleanup(ifmt, ofmt, parser, codec_ctx, map, sorted);
	return ret;
}

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