这是我在使用 ffmpeg 时见过的最奇怪的事情之一。
这是场景 - 我们从 IONODE ION-E100 编码器获取视频片段，该片段以 h264 编码。我可以在 VLC 中很好地查看素材，并且可以使用ffmpeg和将其复制到另一个视频中-c:v copy。当我尝试使用以下命令从电影中提取一个 FPS 时，就会出现问题：
ffmpeg -i testmovie.mp4 -r 1 -vf 640:-2 -q:v 18 -loglevel error /tmp/tmp/extraction_%04d.jpeg
这应该做的是浏览电影并每秒提取一帧，然后将帧转储到文件/tmp/tmp/extraction_0001.jpeg, /tmp/tmp/extraction_0002.jpeg, ..., /tmp/tmp/extraction_000X.jpeg中。它应该在到达视频结尾时结束。
现在，当我运行这个命令时发生的奇怪的事情是它会在一个紧密的循环中运行，将数万或数十万个图像写入磁盘，直到磁盘已满，此时命令失败。所有提取的图像彼此完全相同。
这是视频上的 ffmpeg stats 输出
ffmpeg version 3.2.2 Copyright (c) 2000-2016 the FFmpeg developers
built with Apple LLVM version 8.0.0 (clang-800.0.42.1)
configuration: --prefix=/usr/local/Cellar/ffmpeg/3.2.2 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-libmp3lame --enable-libx264 --enable-libxvid --enable-opencl --disable-lzma --enable-vda
libavutil 55. 34.100 / 55. 34.100
libavcodec 57. 64.101 / 57. 64.101
libavformat 57. 56.100 / 57. 56.100
libavdevice 57. 1.100 / 57. 1.100
libavfilter 6. 65.100 / 6. 65.100
libavresample 3. 1. 0 / 3. 1. 0
libswscale 4. 2.100 / 4. 2.100
libswresample 2. 3.100 / 2. 3.100
libpostproc 54. 1.100 / 54. 1.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/Users/john/ionode/test2.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
title : /videoinput_1:0/h264_1/media.stm
encoder : Lavf57.56.100
Duration: 00:00:16.52, start: -9791.427750, bitrate: 2165 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 2119 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 8000 Hz, mono, fltp, 236 kb/s (default)
Metadata:
handler_name : SoundHandler
（注意start: -9791.427750值，这是什么？）
以下是素材的编码细节：
{
"programs": [
],
"streams": [
{
"index": 0,
"codec_name": "h264",
"codec_long_name": "H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10",
"profile": "High",
"codec_type": "video",
"codec_time_base": "1/50",
"codec_tag_string": "avc1",
"codec_tag": "0x31637661",
"width": 1920,
"height": 1080,
"coded_width": 1920,
"coded_height": 1080,
"has_b_frames": 2,
"sample_aspect_ratio": "1:1",
"display_aspect_ratio": "16:9",
"pix_fmt": "yuv420p",
"level": 40,
"chroma_location": "left",
"refs": 1,
"is_avc": "true",
"nal_length_size": "4",
"r_frame_rate": "25/1",
"avg_frame_rate": "25/1",
"time_base": "1/12800",
"start_pts": 0,
"start_time": "0.000000",
"duration_ts": 211456,
"duration": "16.520000",
"bit_rate": "2119813",
"bits_per_raw_sample": "8",
"nb_frames": "413",
"disposition": {
"default": 1,
"dub": 0,
"original": 0,
"comment": 0,
"lyrics": 0,
"karaoke": 0,
"forced": 0,
"hearing_impaired": 0,
"visual_impaired": 0,
"clean_effects": 0,
"attached_pic": 0,
"timed_thumbnails": 0
},
"tags": {
"language": "und",
"handler_name": "VideoHandler"
}
}
]
}
这里是要使用的示例视频的链接：http ://s000.tinyupload.com/?file_id= 03169189167771012515（这是一个 5MB 的视频文件）
我对实际情况的唯一线索是从编码器获取视频的命令的错误输出：
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823640, current: -630275919; changing to -629823639. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823639, current: -630274895; changing to -629823638. This may result in incorrect timestamps in the output file.
frame= 124 fps= 21 q=28.0 size= 41kB time=00:00:02.60 bitrate= 128.8kbits/s dup=26 drop=4 spee[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823638, current: -630273871; changing to -629823637. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823637, current: -630272847; changing to -629823636. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823636, current: -630271824; changing to -629823635. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823635, current: -630270800; changing to -629823634. This may result in incorrect timestamps in the output file.
frame= 124 fps= 19 q=28.0 size= 43kB time=00:00:02.60 bitrate= 137.0kbits/s dup=26 drop=4 spee[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823634, current: -630269776; changing to -629823633. This may result in incorrect timestamps in the output file.
[aac @ 0x7faa1a832000] Queue input is backward in time
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823633, current: -630268752; changing to -629823632. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823632, current: -630267728; changing to -629823631. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823631, current: -630513833; changing to -629823630. This may result in incorrect timestamps in the output file.
frame= 124 fps= 18 q=28.0 size= 46kB time=00:00:02.60 bitrate= 145.4kbits/s dup=26 drop=4 spee[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823630, current: -630512810; changing to -629823629. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823629, current: -630511786; changing to -629823628. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823628, current: -630510762; changing to -629823627. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823627, current: -630509738; changing to -629823626. This may result in incorrect timestamps in the output file.
frame= 124 fps= 17 q=28.0 size= 49kB time=00:00:02.60 bitrate= 153.6kbits/s dup=26 drop=4 spee[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823626, current: -630508714; changing to -629823625. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823625, current: -630507690; changing to -629823624. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823624, current: -630506667; changing to -629823623. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823623, current: -630505643; changing to -629823622. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823622, current: -630504619; changing to -629823621. This may result in incorrect timestamps in the output file.
frame= 124 fps= 16 q=28.0 size= 52kB time=00:00:02.60 bitrate= 163.5kbits/s dup=26 drop=4 spee[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823621, current: -630503595; changing to -629823620. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823620, current: -630502571; changing to -629823619. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823619, current: -630501548; changing to -629823618. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823618, current: -630500524; changing to -629823617. This may result in incorrect timestamps in the output file.
frame= 124 fps= 15 q=28.0 size= 54kB time=00:00:02.60 bitrate= 171.4kbits/s dup=26 drop=4 spee[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823617, current: -630499500; changing to -629823616. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823616, current: -630498476; changing to -629823615. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823615, current: -630497452; changing to -629823614. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823614, current: -630496428; changing to -629823613. This may result in incorrect timestamps in the output file.
frame= 124 fps= 14 q=28.0 size= 57kB time=00:00:02.60 bitrate= 179.3kbits/s dup=26 drop=4 spee[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823613, current: -630495405; changing to -629823612. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823612, current: -630494381; changing to -629823611. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823611, current: -630493357; changing to -629823610. This may result in incorrect timestamps in the output file.
frame= 124 fps= 13 q=28.0 size= 59kB time=00:00:02.60 bitrate= 185.6kbits/s dup=26 drop=4 spee[aac @ 0x7faa1a832000] Queue input is backward in time
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823610, current: -630492333; changing to -629823609. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823609, current: -630491309; changing to -629823608. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823608, current: -630736398; changing to -629823607. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823607, current: -630735375; changing to -629823606. This may result in incorrect timestamps in the output file.
frame= 124 fps= 12 q=28.0 size= 61kB time=00:00:02.60 bitrate= 193.5kbits/s dup=26 drop=4 spee[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823606, current: -630734351; changing to -629823605. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823605, current: -630733327; changing to -629823604. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823604, current: -630732303; changing to -629823603. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823603, current: -630731279; changing to -629823602. This may result in incorrect timestamps in the output file.
[mp4 @ 0x7faa1a83ba00] Non-monotonous DTS in output stream 0:1; previous: -629823602, current: -630730256; changing to -629823601. This may result in incorrect timestamps in the output file.
frame= 124 fps= 12 q=-1.0 Lsize= 507kB time=00:00:04.84 bitrate= 858.7kbits/s dup=26 drop=4 speed=0.453x
所以我的问题是，为什么这个视频会破坏 ffmpeg？为什么 ffmpeg 会陷入提取图像的紧密循环中，而在视频结束时却没有任何进展？