bash - FFmpeg 破坏 Bash/shell 脚本中的 "while/if"结构 - 如何修复？

Question

我正在尝试从多个文件夹中的一系列 .mp4 视频中提取一定数量的帧。我正在从 CSV 文件中读取变量，其中 CSV 文件的每一行都包含每个剪辑的变量，它们是:“数据集”、“文件名”、“帧标签”、“剪辑目标开始时间”、“剪辑目标结束时间”、“提取率”(以每帧秒数为单位)和“排除原因”。

我正在使用 while/if 循环结构，因此我可以避免尝试处理从我们的项目中排除的视频。

当我只打印出变量名时，while/if 循环结构似乎运行良好。但是，当我插入一行 ffmpeg 代码时，下一个视频的变量分配(即从 CSV 文件中读取的以下行)变得困惑。

这是没有 ffmpeg 行的代码，它似乎可以工作(所有“echo”语句都只是作为调试工具来跟踪变量分配):

IFS=‘,’
while read DATASET FILENAME FRAMELABEL TARGET_START TARGET_END TOTAL_DURATION EXTRACT_RATE REASON_FOR_EXCLUSION 
do  
echo “PRE FFMPEG”
echo “dataset and filename are “ $DATASET/$FILENAME
echo “target start is “ $TARGET_START
echo “target end is “ $TARGET_END

if [ $TARGET_START != EXCLUDED ] && [ $TARGET_START != Target_start ]
then
IFS=‘:’ 
read -r -a fps_array <<< "$EXTRACT_RATE"
IFS=‘,’
let "secs = ${fps_array[0]}*3600 + ${fps_array[1]}*60 + ${fps_array[2]}"
FPS_RATE=$(echo "scale=20;1/$secs" | bc)

echo “AFTER FFMPEG”
echo “dataset and filename are “ $DATASET/$FILENAME
echo “target start is “ $TARGET_START
echo “target end is “ $TARGET_END

fi
done < Test_Key.csv`

上面代码的输出如下所示，这是正确的(我有 2 个文件夹，“cats”和“es123”，每个文件夹有两个视频；其中一个 es123 视频被排除在帧提取之外):

“PRE FFMPEG”
“dataset and filename are “ cats/IMG_3460
“target start is “ 0:00:02
“target end is “ 0:00:24
“AFTER FFMPEG”
“dataset and filename are “ cats/IMG_3460
“target start is “ 0:00:02
“target end is “ 0:00:24
“PRE FFMPEG”
“dataset and filename are “ cats/IMG_4137
“target start is “ 0:00:10
“target end is “ 0:00:40
“AFTER FFMPEG”
“dataset and filename are “ cats/IMG_4137
“target start is “ 0:00:10
“target end is “ 0:00:40
“PRE FFMPEG”
“dataset and filename are “ es123/IMG_4577
“target start is “ EXCLUDED
“target end is “
“PRE FFMPEG”
“dataset and filename are “ es123/IMG_4839
“target start is “ 0:00:05
“target end is “ 0:00:25
“AFTER FFMPEG”
“dataset and filename are “ es123/IMG_4839
“target start is “ 0:00:05
“target end is “ 0:00:25

但是，然后我尝试添加我的 ffmpeg 行，以进行实际的帧提取:

IFS=‘,’
while read DATASET FILENAME FRAMELABEL TARGET_START TARGET_END TOTAL_DURATION EXTRACT_RATE REASON_FOR_EXCLUSION 
do  
echo “PRE FFMPEG”
echo “dataset and filename are “ $DATASET/$FILENAME
echo “target start is “ $TARGET_START
echo “target end is “ $TARGET_END

if [ $TARGET_START != EXCLUDED ] && [ $TARGET_START != Target_start ]
then
IFS=‘:’ 
read -r -a fps_array <<< "$EXTRACT_RATE"
IFS=‘,’
let "secs = ${fps_array[0]}*3600 + ${fps_array[1]}*60 + ${fps_array[2]}"
FPS_RATE=$(echo "scale=20;1/$secs" | bc)

ffmpeg -i $DATASET/$FILENAME.mp4 -ss $TARGET_START -to $TARGET_END -vf fps=$FPS_RATE ${DATASET}/${DATASET}_${FILENAME}_%03d.jpg

echo “AFTER FFMPEG”
echo “dataset and filename are “ $DATASET/$FILENAME
echo “target start is “ $TARGET_START
echo “target end is “ $TARGET_END

fi
done < Test_Key.csv

结果是第一部电影的帧被正确提取，但第二部电影的变量名完全搞砸了(当然，代码会因为视频名称错误而失败)。您可以在我用来跟踪变量命名的“echo”语句中看到这一点，这些语句变为:

“PRE FFMPEG”
“dataset and filename are “ cats/IMG_3460
“target start is “ 0:00:02
“target end is “ 0:00:24
“AFTER FFMPEG”
“dataset and filename are “ cats/IMG_3460
“target start is “ 0:00:02
“target end is “ 0:00:24
“PRE FFMPEG”
“dataset and filename are “ IMG_4839/es123_2
“target start is “ 0:00:25
“target end is “ 0:00:20

有谁知道为什么 ffmpeg 会影响 while/if 循环结构的功能？ (我对 shell 脚本很陌生，如果这很明显，我很抱歉)。我能做些什么来解决它？

谢谢!

作为引用，这里是当我运行包含 ffmpeg 行的代码时打印的所有内容——出现了一些我不太理解的解析错误，但可能会解释这一点。

“PRE FFMPEG”
“dataset and filename are “ cats/IMG_3460
“target start is “ 0:00:02
“target end is “ 0:00:24
ffmpeg version 4.2.2-tessus  https://evermeet.cx/ffmpeg/  Copyright (c) 2000-2019 the FFmpeg developers
  built with Apple clang version 11.0.0 (clang-1100.0.33.16)
  configuration: --cc=/usr/bin/clang --prefix=/opt/ffmpeg --extra-version=tessus --enable-avisynth --enable-fontconfig --enable-gpl --enable-libaom --enable-libass --enable-libbluray --enable-libdav1d --enable-libfreetype --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libmysofa --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenh264 --enable-libopenjpeg --enable-libopus --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvmaf --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libzimg --enable-libzmq --enable-libzvbi --enable-version3 --pkg-config-flags=--static --disable-ffplay
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'cats/IMG_3460.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
  Duration: 00:00:25.15, start: 0.000000, bitrate: 6866 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1080x1920, 6796 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 59.94 tbc (default)
    Metadata:
      handler_name    : Core Media Video
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 69 kb/s (default)
    Metadata:
      handler_name    : Core Media Audio
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> mjpeg (native))
Press [q] to stop, [?] for help

Enter command: <target>|all <time>|-1 <command>[ <argument>]

Parse error, at least 3 arguments were expected, only 1 given in string 'ats,IMG_4137,cats_2,0:00:10,0:00:40,0:00:30,0:00:03,none,,'
[swscaler @ 0x7fd3fc953400] deprecated pixel format used, make sure you did set range correctly
Output #0, image2, to 'cats/cats_IMG_3460_%03d.jpg':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
    Stream #0:0(und): Video: mjpeg, yuvj420p(pc), 1080x1920, q=2-31, 200 kb/s, 0.50 fps, 0.50 tbn, 0.50 tbc (default)
    Metadata:
      handler_name    : Core Media Video
      encoder         : Lavc58.54.100 mjpeg
    Side data:
      cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: -1
frame=    8 fps=3.2 q=1.6 size=N/A time=00:00:16.00 bitrate=N/A speed=6.33x    0.00 bitrate=N/A speed=6.59x    
Enter command: <target>|all <time>|-1 <command>[ <argument>]

Parse error, at least 3 arguments were expected, only 1 given in string 'LUDED,,,,boring,,'
frame=   11 fps=3.0 q=2.6 L00120000000000000000000000000000size=N/A time=00:00:22.00 bitrate=N/A speed=6.06x    
video:803kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
“AFTER FFMPEG”
“dataset and filename are “ cats/IMG_3460
“target start is “ 0:00:02
“target end is “ 0:00:24
“PRE FFMPEG”
“dataset and filename are “ IMG_4839/es123_2
“target start is “ 0:00:25
“target end is “ 0:00:20
-bash: let: secs = none*3600 + *60 + : syntax error: operand expected (error token is "*60 + ")
ffmpeg version 4.2.2-tessus  https://evermeet.cx/ffmpeg/  Copyright (c) 2000-2019 the FFmpeg developers
  built with Apple clang version 11.0.0 (clang-1100.0.33.16)
  configuration: --cc=/usr/bin/clang --prefix=/opt/ffmpeg --extra-version=tessus --enable-avisynth --enable-fontconfig --enable-gpl --enable-libaom --enable-libass --enable-libbluray --enable-libdav1d --enable-libfreetype --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libmysofa --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenh264 --enable-libopenjpeg --enable-libopus --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvmaf --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-libzimg --enable-libzmq --enable-libzvbi --enable-version3 --pkg-config-flags=--static --disable-ffplay
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
IMG_4839/es123_2.mp4: No such file or directory
“AFTER FFMPEG”
“dataset and filename are “ IMG_4839/es123_2
“target start is “ 0:00:25
“target end is “ 0:00:20

Answer 1

来自 FFmpeg 的手册:

-stdin Enable interaction on standard input. On by default unless standard input is used as an input. To explicitly disable interaction you need to specify "-nostdin".

在您的情况下，通过 -nostdin到 FFmpeg CLI proc 就足够了。

如果您有多个循环，您还可以使用不同的 FD，例如:

while read DATASET FILENAME FRAMELABEL TARGET_START TARGET_END TOTAL_DURATION EXTRACT_RATE REASON_FOR_EXCLUSION  <&3 ;do 
...
done 3< Test_Key.csv 

这里的关键变化当然是 3 .