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Thanks, I see there's talking about the frames problem, but not sure if it's just solved in a new version or I should change some parameters, I'll give it a try

by narag 4y ago

Thanks, I see there's talking about the frames problem, but not sure if it's just solved in a new version or I should change some parameters, I'll give it a try next time I need to use the program.

pessimizer 4y ago
https://superuser.com/questions/138331/using-ffmpeg-to-cut-up-video/704118#704118 https://superuser.com/questions/138331/using-ffmpeg-to-cut-u... Looks like the ordering of the parameters makes a difference.
- narag 4y ago
  That seems another different issue. The problem, as Wowfunhappy explained, is that the codecs compress the frames making a diff with the previous frames. So if you start in a frame that depends on other frames that you don't want to include in the clip, there's information missing. The result is that the clip starts playing the sound, but with all-black video for a few seconds. In the previous link there are a couple of solutions that might work. One is "recoding", that's somehow ambiguous: could be understood as changing the codec, but also making a new compression from the decompressed frames. I have the program in another computer so I can't test it now, but I certainly will.
  - pessimizer 4y ago
    I understand the problem. >Also note this important point from that page: "If you use -ss with -c:v copy, the resulting bitstream might end up being choppy, not playable, or out of sync with the audio stream, since ffmpeg is forced to only use/split on i-frames." > This means you need to re-encode the video, even if you want to just copy it, or risk it being choppy and out of sync. You could try just -c copy first, but if the video sucks you'll need to re-do it. From the link. ----- edit: if it aids understanding, I think i-frame means "interpolated frame" i.e. frame that depends on the previous and next frames. edit2: and "-c:v copy" means don't transcode (or "recode" as you say) the video, but simply copy it.

by narag 4y ago

Thanks, I see there's talking about the frames problem, but not sure if it's just solved in a new version or I should change some parameters, I'll give it a try next time I need to use the program.

pessimizer 4y ago

https://superuser.com/questions/138331/using-ffmpeg-to-cut-up-video/704118#704118 https://superuser.com/questions/138331/using-ffmpeg-to-cut-u... Looks like the ordering of the parameters makes a difference.

narag 4y ago
That seems another different issue. The problem, as Wowfunhappy explained, is that the codecs compress the frames making a diff with the previous frames. So if you start in a frame that depends on other frames that you don't want to include in the clip, there's information missing. The result is that the clip starts playing the sound, but with all-black video for a few seconds. In the previous link there are a couple of solutions that might work. One is "recoding", that's somehow ambiguous: could be understood as changing the codec, but also making a new compression from the decompressed frames. I have the program in another computer so I can't test it now, but I certainly will.
- pessimizer 4y ago
  I understand the problem. >Also note this important point from that page: "If you use -ss with -c:v copy, the resulting bitstream might end up being choppy, not playable, or out of sync with the audio stream, since ffmpeg is forced to only use/split on i-frames." > This means you need to re-encode the video, even if you want to just copy it, or risk it being choppy and out of sync. You could try just -c copy first, but if the video sucks you'll need to re-do it. From the link. ----- edit: if it aids understanding, I think i-frame means "interpolated frame" i.e. frame that depends on the previous and next frames. edit2: and "-c:v copy" means don't transcode (or "recode" as you say) the video, but simply copy it.