HEVC流Muxing/Demuxing异常：重构视频时长帧率不符问题咨询

问题详情 #

对HEVC流执行分割（Muxing）与合并（Demuxing）操作后，重构视频出现时长缩短约3秒、帧率从24变为24.33的参数偏差问题，具体操作步骤如下：

1. 用segment muxer分割为5秒片段 #

ffmpeg -y -r 24 -i input.mp4 -map 0:v:0? -c copy \
-f segment -segment_time 5 -reset_timestamps 1 ./segments/%05d.mp4

2. 用concat demuxer合并片段 #

PWD=`pwd`
ffmpeg -y -f concat -safe 0 -i <( echo file ${PWD}'/segments/00000.mp4';  \
echo file ${PWD}'/segments/00001.mp4';  echo file ${PWD}'/segments/00002.mp4';  \
echo file ${PWD}'/segments/00003.mp4';  echo file ${PWD}'/segments/00004.mp4';  \
echo file ${PWD}'/segments/00005.mp4';  echo file ${PWD}'/segments/00006.mp4';  \
echo file ${PWD}'/segments/00007.mp4';  echo file ${PWD}'/segments/00008.mp4';  \
echo file ${PWD}'/segments/00009.mp4';  echo file ${PWD}'/segments/00010.mp4';  \
echo file ${PWD}'/segments/00011.mp4';  echo file ${PWD}'/segments/00012.mp4';  \
echo file ${PWD}'/segments/00013.mp4';  echo file ${PWD}'/segments/00014.mp4';  \
echo file ${PWD}'/segments/00015.mp4';  echo file ${PWD}'/segments/00016.mp4';  \
echo file ${PWD}'/segments/00017.mp4';  echo file ${PWD}'/segments/00018.mp4';  \
echo file ${PWD}'/segments/00019.mp4';  echo file ${PWD}'/segments/00020.mp4';  \
echo file ${PWD}'/segments/00021.mp4';  echo file ${PWD}'/segments/00022.mp4';  \
echo file ${PWD}'/segments/00023.mp4';  echo file ${PWD}'/segments/00024.mp4';  \
echo file ${PWD}'/segments/00025.mp4';  echo file ${PWD}'/segments/00026.mp4';  \
echo file ${PWD}'/segments/00027.mp4';  echo file ${PWD}'/segments/00028.mp4';  \
echo file ${PWD}'/segments/00029.mp4';  echo file ${PWD}'/segments/00030.mp4';  \
echo file ${PWD}'/segments/00031.mp4';  echo file ${PWD}'/segments/00032.mp4';  \
echo file ${PWD}'/segments/00033.mp4';  echo file ${PWD}'/segments/00034.mp4';  \
echo file ${PWD}'/segments/00035.mp4';  echo file ${PWD}'/segments/00036.mp4';  \
echo file ${PWD}'/segments/00037.mp4'; ) -map 0 -c copy -r 24 -brand mp42 \
-video_track_timescale 600 -tag:v hvc1 output.mp4

问题根源 #

1. 强制帧率导致时间戳偏差：分割时指定-r 24，与原视频6秒IDR间隔、原生时间基准不匹配，引发片段时间戳计算错误，丢帧或重复统计时间。
2. 时间戳衔接异常：分割时-reset_timestamps 1让每个片段时间戳从0开始，合并时未正确处理时间戳衔接，导致总时长计算失真。
3. 时间基准与帧率强制冲突：合并时手动设置-video_track_timescale 600和-r 24，若原视频时间基准并非600，会导致帧率计算异常（24.33为实际帧总数除以错误时长的结果）。

修复方案 #

1. 修正分割命令（保留原生时间属性） #

移除强制帧率参数-r 24，让FFmpeg自动读取原视频时间基准与帧率，同时添加参数确保片段时间戳合规：

ffmpeg -y -i input.mp4 -map 0:v:0? -c copy \
-f segment -segment_time 5 -reset_timestamps 1 -segment_format_options movflags=+faststart ./segments/%05d.mp4

2. 修正合并命令（自动继承片段属性） #

移除强制帧率-r 24与手动时间基准设置，改用循环遍历片段文件，避免手动列举的繁琐与错误：

PWD=$(pwd)
ffmpeg -y -f concat -safe 0 -i <(for file in ./segments/*.mp4; do echo "file '${PWD}/${file}'"; done) \
-map 0 -c copy -brand mp42 -tag:v hvc1 output.mp4

3. 参数验证 #

用ffprobe对比原视频与输出视频的核心参数：

# 检查原视频参数
ffprobe -v error -select_streams v:0 -show_entries stream=r_frame_rate,duration,time_base -of default=noprint_wrappers=1 input.mp4

# 检查输出视频参数
ffprobe -v error -select_streams v:0 -show_entries stream=r_frame_rate,duration,time_base -of default=noprint_wrappers=1 output.mp4

内容的提问来源于stack exchange，提问作者Adeel Abbas