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All Versions How to convert FLVs to MP4 fast without re-encoding


New Member
hey guys question I was converting these yesterday and no issue but today every time I try to convert I keep getting this error


New Member
Thank you for your help. Article was great. I downloaded the ffmpeg binary. Used the static build for OS X 10.11. Then I tried your command:

ffmpeg -i input.flv -c copy -copyts output.mp4

Gave me an error. So I did some searching and it turns out that it didn't like the word "copy" in the command. Ran it again without like so:

ffmpeg -i input.flv -c -copyts output.mp4

Seems to be working fine now. Not sure why that would be.


Update: Nope, you are right. Your syntax is correct and I just can't copy and paste correctly. This is the right format:

ffmpeg -i input.flv -c copy -copyts output.mp4

Thank you very much!
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New Member
Hello, I ran into an unexpected issue that I am having trouble solving. When the command is executed, Windows cannot find the converted the file. Windows search was used and the file did not show. Furthermore, when the command was executed using the same parameters, the command prompt prompted that the file existed. Then this command was re-ran with a different input file and the same thing occurred. If there is any solution to this problem that I am not aware please let me know. Thank you very much and sorry for any inconvenience

andreas krebs

New Member
okay so i´m a bit new to this hole video format but when i convert it from a flv to mp4 i lose the video but the audio is still there like nothing had happend.. anyone who can help me whit this?


New Member
Yes it works, but flv is a simple container like mp4, why just changing container goes from 44 Mb of the flv to 444 Mb of the mp4?


New Member
Hi, I finally finished setting up ffmpeg and getting windows to find the directory in the command prompt. I don't really know what I'm doing but I got the error (.flv File Name): Invalid data found when processing input.


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New Member
This guide used to link to software called FLV Extract. Now that OBS Studio has a built-in FLV to MP4 remux tool, this guide no longer mentions FLV Extract, but there is an advantage to the FLV Extract software vs the built-in remux tool in OBS. That advantage is that the remuxed MP4 from FLV Extract has a constant frame rate setting instead of a variable frame rate setting like what the OBS tool and others do.

The reason why this matters is because of the video software I use, which is Cyberlink PowerDirector. When working with MP4 recordings with a constant frame rate, PowerDirector is then able to use SVRT (Smart Video Rendering Technology) with the video, which does no re-encoding of the video except where edits are done. With the variable frame rate setting, SVRT can't be used.

I just want to post this here for information sake. FLV Extract (2.2) can still be found with searching if anyone needs a constant frame rate MP4 file from an FLV file or uses PowerDirector like I do.
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death kitty

New Member
1. I got this old video from weebls-stuff called Death Kitty and the Fat Man by Megat Diam:

2. I used Sothink SWF Decompiler to get the FLV and MP3 files from the SWF (if you know a free/open source thing to get stuff from SWF please say)

3. I merged the FLV video file and the MP3 audio file together with:
ffmpeg -i "250.mp3" -i "250.flv" -acodec copy -vcodec copy "250merged.flv"

4. I then tried to convert the FLV to MP4 by following the instructions from this website (you are top in the world for search results for lossless flv convert, sorry if it's slightly offtopic but hopefully it can help others too if any answer!):
ffmpeg -i 250merged.flv -c copy -copyts 250merged.mp4

ffmpeg version N-71816-g02001ad Copyright (c) 2000-2015 the FFmpeg developers
built with gcc 4.9.2 (GCC)
configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnu
tls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libdcadec --enable-libfreetype --enable-libgme --enab
le-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable
-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --ena
ble-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --e
nable-libxavs --enable-libxvid --enable-lzma --enable-decklink --enable-zlib
libavutil 54. 23.101 / 54. 23.101
libavcodec 56. 35.101 / 56. 35.101
libavformat 56. 31.100 / 56. 31.100
libavdevice 56. 4.100 / 56. 4.100
libavfilter 5. 14.100 / 5. 14.100
libswscale 3. 1.101 / 3. 1.101
libswresample 1. 1.100 / 1. 1.100
libpostproc 53. 3.100 / 53. 3.100
Input #0, flv, from '250merged.flv':
encoder : Lavf56.31.100
Duration: 00:02:26.84, start: 0.000000, bitrate: 245 kb/s
Stream #0:0: Video: flv1, yuv420p, 550x400, 25 fps, 25 tbr, 1k tbn, 1k tbc
Stream #0:1: Audio: mp3, 22050 Hz, mono, s16p, 24 kb/s
[mp4 @ 00000000055f1820] Codec for stream 0 does not use global headers but container format requires global headers
[mp4 @ 00000000055f1820] Codec for stream 1 does not use global headers but container format requires global headers

[mp4 @ 00000000055f1820] Could not find tag for codec flv1 in stream #0, codec not currently supported in container
Output #0, mp4, to 'output.mp4':
encoder : Lavf56.31.100
Stream #0:0: Video: flv1, yuv420p, 550x400, q=2-31, 25 fps, 25 tbr, 1k tbn, 1k tbc
Stream #0:1: Audio: mp3 (i[0][0][0] / 0x0069), 22050 Hz, mono, 24 kb/s
Stream mapping:
Stream #0:0 -> #0:0 (copy)
Stream #0:1 -> #0:1 (copy)

Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument

5. There is no 5, it doesn't work :( I guess maybe FLV1 is an old format or something? I tried converting just the 250.flv video file (without the Mp3) on it's own and got the same error (
[mp4 @ 000000000050ae40] Could not find tag for codec flv1 in stream #0, codec not currently supported in container
Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument)


Obviously I don't want to make the quality worse so lossless is important and not transcoding the video :(

Thank you for any help anyone!

( The SWF Flash file also has an ending page with the credits inside the file itself, which I screenshot-recorded a Mp4 of with Nvidia Geforce Experience/shadowplay, I want to join that onto the end of the actual video file so it's like the original SWF flash file, but that would be much easier hopefully if I could only get the convert to work :( )
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