为啥这个 ffmpeg 过滤器会导致“Invalid Size”错误？
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【中文标题】为啥这个 ffmpeg 过滤器会导致“Invalid Size”错误？【英文标题】：Why does this ffmpeg filter result in an "Invalid Size" error?为什么这个 ffmpeg 过滤器会导致“Invalid Size”错误？ 【发布时间】：2019-04-10 16:41:45 【问题描述】：为什么我会看到此错误消息：
[Parsed_scale_0 @ 0x559a264c28a0] 大小无效'if(gt(iw'
[AVFilterGraph @ 0x559a268a19e0] 初始化过滤器“缩放”时出错
with args 'if(gt(iw' 初始化复杂过滤器时出错。
参数无效
尝试使用 ffmpeg 和以下复杂过滤器裁剪视频时：
ffmpeg -f mp4 -ss 01:24 \
-i https://storage.googleapis.com/bucket/video.mp4 \
-y \
-filter_complex scale='if(gt(iw,ih),-1,616):if(gt(iw,ih),1440,-1)', crop=1440:616 \
-an \
-vcodec libx264 \
-r 60 -pix_fmt yuv420p \
-movflags faststart \
-f mp4 \
-t 1 \
/tmp/asset.1554913197962.mp4
如果相关，这里是 ffprobe 的输出：
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'https://storage.googleapis.com/bucket/video.mp4':
Metadata:
major_brand : isom
minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf57.56.101
Duration: 00:02:53.76, start: 0.000000, bitrate: 2910 kb/s
Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 2777 kb/s, 29.97 fps, 29.97 tbr, 90k tbn, 59.94 tbc (default)
Metadata:
handler_name : VideoHandler
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
Metadata:
handler_name : SoundHandler
"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": "1001/60000",
"codec_tag_string": "avc1",
"codec_tag": "0x31637661",
"width": 1920,
"height": 1080,
"coded_width": 1920,
"coded_height": 1080,
"has_b_frames": 1,
"sample_aspect_ratio": "1:1",
"display_aspect_ratio": "16:9",
"pix_fmt": "yuv420p",
"level": 40,
"color_range": "tv",
"color_space": "bt709",
"color_transfer": "bt709",
"color_primaries": "bt709",
"chroma_location": "left",
"refs": 1,
"is_avc": "true",
"nal_length_size": "4",
"r_frame_rate": "30000/1001",
"avg_frame_rate": "30000/1001",
"time_base": "1/90000",
"start_pts": 0,
"start_time": "0.000000",
"duration_ts": 15633630,
"duration": "173.707000",
"bit_rate": "2777254",
"bits_per_raw_sample": "8",
"nb_frames": "5206",
"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"
,
"index": 1,
"codec_name": "aac",
"codec_long_name": "AAC (Advanced Audio Coding)",
"profile": "LC",
"codec_type": "audio",
"codec_time_base": "1/44100",
"codec_tag_string": "mp4a",
"codec_tag": "0x6134706d",
"sample_fmt": "fltp",
"sample_rate": "44100",
"channels": 2,
"channel_layout": "stereo",
"bits_per_sample": 0,
"r_frame_rate": "0/0",
"avg_frame_rate": "0/0",
"time_base": "1/44100",
"start_pts": 0,
"start_time": "0.000000",
"duration_ts": 7662596,
"duration": "173.755011",
"bit_rate": "125588",
"max_bit_rate": "125588",
"nb_frames": "7483",
"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": "eng",
"handler_name": "SoundHandler"
],
"format":
"filename": "https://storage.googleapis.com/bucket/video.mp4",
"nb_streams": 2,
"nb_programs": 0,
"format_name": "mov,mp4,m4a,3gp,3g2,mj2",
"format_long_name": "QuickTime / MOV",
"start_time": "0.000000",
"duration": "173.755000",
"size": "63209767",
"bit_rate": "2910294",
"probe_score": 100,
"tags":
"major_brand": "isom",
"minor_version": "512",
"compatible_brands": "isomiso2avc1mp41",
"encoder": "Lavf57.56.101"
【问题讨论】：
【参考方案1】：将整个过滤器图用双引号括起来：
"scale='if(gt(iw,ih),-1,616):if(gt(iw,ih),1440,-1)', crop=1440:616"
...或转义逗号：
scale='if(gt(iw\,ih)\,-1\,616):if(gt(iw\,ih)\,1440\,-1)',crop=1440:616
【讨论】：
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