Flash Tutorials - Herong's Tutorial Examples - v3.03, by Dr. Herong Yang
Video/Audio Stream Concatenation Order
This section provides a tutorial example of concatenation error message when using the 'concat' ffmpeg filter with incorrect video and audio stream order.
As mentioned in the previous section, when using the "concat" filter, the order of how input streams are specified is important. The video input stream must be specified before the audio stream. Here is what mentioned in the "ffmpeg" manual:
The (concat) filter has v+a outputs: first v video outputs, then a audio outputs. There are nx(v+a) inputs: first the inputs for the first segment, in the same order as the outputs, then the inputs for the second segment, etc.
If the audio stream is placed before the video stream, you will get a strange error:
C:\herong>\local\ffmpeg\bin\ffmpeg -i Anchor_Great_Escape.swf -i Spider_Man.swf -filter_complex "[0:0] [0:1] [1:0] [1:1] concat=n=2:v=1:a=1 [a] [v]" -map [a] -map [v] Test.swf Input #0, swf, from 'Anchor_Great_Escape.swf': Duration: 00:01:02.60, start: 0.000000, bitrate: 127 kb/s Stream #0:0: Audio: mp3, 44100 Hz, stereo, s16p, 128 kb/s Stream #0:1: Video: flv1, yuv420p, 416x240, 25 fps, 25 tbr, 25 tbn Input #1, swf, from 'Spider_Man.swf': Duration: 00:01:09.56, start: 0.000000, bitrate: 128 kb/s Stream #1:0: Audio: mp3, 44100 Hz, stereo, s16p, 128 kb/s Stream #1:1: Video: flv1, yuv420p, 416x240, 25 fps, 25 tbr, 25 tbn Stream specifier ':0' in filtergraph description [0:0] [0:1] [1:0] [1:1] concat=n=2:v=1:a=1 [a] [v] matches no streams.
The error message in the above output is a little bit confusing: "Stream specifier ':0' in filtergraph description [0:0] [0:1] [1:0] [1:1] concat=n=2:v=1:a=1 [a] [v] matches no streams." It sounds like "ffmpeg" could not find the specified stream [0:0] input stream.
The error message should be saying "[0:0] is not a video stream. I am expecting a video stream."
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