ffmpeg transcode twice compress further?
I have a collection of avi videos (say A).
I first convert them into MPEG4 Part2 (say B) using ffmpeg -i ${inname} -vf scale=340:256,setsar=1:1 -q:v 1 -c:v mpeg4 -g 12 -f rawvideo ${outname}. The total file size is 3.5G.
Then using B as input, I apply the same command to transcode B again into C, which has size 3.1G.
I thought B and C have the same format and thus should have the same file size? Why not and how can I resolve it to make sure no information loss in the second transcoding process?
video ffmpeg compression transcode mpeg4
asked Dec 22 '18 at 21:16
apoliverapoliver
61
|
show 2 more comments
I have a collection of avi videos (say A).
I first convert them into MPEG4 Part2 (say B) using ffmpeg -i ${inname} -vf scale=340:256,setsar=1:1 -q:v 1 -c:v mpeg4 -g 12 -f rawvideo ${outname}. The total file size is 3.5G.
Then using B as input, I apply the same command to transcode B again into C, which has size 3.1G.
I thought B and C have the same format and thus should have the same file size? Why not and how can I resolve it to make sure no information loss in the second transcoding process?
video ffmpeg compression transcode mpeg4
asked Dec 22 '18 at 21:16
apoliverapoliver
61
2
Transcoding always looses data. Video encoding is lossy.
– Mokubai♦
Dec 22 '18 at 22:34
Thanks. But B and C have the same formats such as block size, number of p-frames, etc. It should be possible to make it lossless -- consider just duplicating B as C, right?
– apoliver
Dec 22 '18 at 23:42
By simply copying the video to a new container, yes. By transcoding, no. Ffmpeg supports copying using-c:v copy
– Mokubai♦
Dec 22 '18 at 23:47
Thanks. But my goal is not just copying. I'd like to learn which factors lead to this loss in the second stage and I want to avoid such second quality loss when I use other different codecs.
– apoliver
Dec 23 '18 at 0:49
BTW, by copying the video to a new container,-c:v copy, do you mean that, say copy a video from H.264 to MPEG4 Part2, the format can still be changed to accommodate MPEG4 Part2 but no information loss? Thanks. Sorry that I am new to video compression... I guess the answer is no because I need to specify-c:v mpeg4? or I just need to name the output as .mp4 ?
– apoliver
Dec 26 '18 at 16:57
|
show 2 more comments
I have a collection of avi videos (say A).
I first convert them into MPEG4 Part2 (say B) using ffmpeg -i ${inname} -vf scale=340:256,setsar=1:1 -q:v 1 -c:v mpeg4 -g 12 -f rawvideo ${outname}. The total file size is 3.5G.
Then using B as input, I apply the same command to transcode B again into C, which has size 3.1G.
I thought B and C have the same format and thus should have the same file size? Why not and how can I resolve it to make sure no information loss in the second transcoding process?
video ffmpeg compression transcode mpeg4
asked Dec 22 '18 at 21:16
apoliverapoliver
61
I have a collection of avi videos (say A).
I first convert them into MPEG4 Part2 (say B) using ffmpeg -i ${inname} -vf scale=340:256,setsar=1:1 -q:v 1 -c:v mpeg4 -g 12 -f rawvideo ${outname}. The total file size is 3.5G.
Then using B as input, I apply the same command to transcode B again into C, which has size 3.1G.
I thought B and C have the same format and thus should have the same file size? Why not and how can I resolve it to make sure no information loss in the second transcoding process?
video ffmpeg compression transcode mpeg4
video ffmpeg compression transcode mpeg4
asked Dec 22 '18 at 21:16
apoliverapoliver
61
asked Dec 22 '18 at 21:16
apoliverapoliver
61
asked Dec 22 '18 at 21:16
apoliverapoliver
61
asked Dec 22 '18 at 21:16
apoliverapoliver
61
asked Dec 22 '18 at 21:16
apoliverapoliver
61
61
2
Transcoding always looses data. Video encoding is lossy.
– Mokubai♦
Dec 22 '18 at 22:34
Thanks. But B and C have the same formats such as block size, number of p-frames, etc. It should be possible to make it lossless -- consider just duplicating B as C, right?
– apoliver
Dec 22 '18 at 23:42
By simply copying the video to a new container, yes. By transcoding, no. Ffmpeg supports copying using-c:v copy
– Mokubai♦
Dec 22 '18 at 23:47
Thanks. But my goal is not just copying. I'd like to learn which factors lead to this loss in the second stage and I want to avoid such second quality loss when I use other different codecs.
– apoliver
Dec 23 '18 at 0:49
BTW, by copying the video to a new container,-c:v copy, do you mean that, say copy a video from H.264 to MPEG4 Part2, the format can still be changed to accommodate MPEG4 Part2 but no information loss? Thanks. Sorry that I am new to video compression... I guess the answer is no because I need to specify-c:v mpeg4? or I just need to name the output as .mp4 ?
– apoliver
Dec 26 '18 at 16:57
|
show 2 more comments
2
Transcoding always looses data. Video encoding is lossy.
– Mokubai♦
Dec 22 '18 at 22:34
Thanks. But B and C have the same formats such as block size, number of p-frames, etc. It should be possible to make it lossless -- consider just duplicating B as C, right?
– apoliver
Dec 22 '18 at 23:42
By simply copying the video to a new container, yes. By transcoding, no. Ffmpeg supports copying using-c:v copy
– Mokubai♦
Dec 22 '18 at 23:47
Thanks. But my goal is not just copying. I'd like to learn which factors lead to this loss in the second stage and I want to avoid such second quality loss when I use other different codecs.
– apoliver
Dec 23 '18 at 0:49
BTW, by copying the video to a new container,-c:v copy, do you mean that, say copy a video from H.264 to MPEG4 Part2, the format can still be changed to accommodate MPEG4 Part2 but no information loss? Thanks. Sorry that I am new to video compression... I guess the answer is no because I need to specify-c:v mpeg4? or I just need to name the output as .mp4 ?
– apoliver
Dec 26 '18 at 16:57
2
2
Transcoding always looses data. Video encoding is lossy.
– Mokubai♦
Dec 22 '18 at 22:34
Transcoding always looses data. Video encoding is lossy.
– Mokubai♦
Dec 22 '18 at 22:34
Thanks. But B and C have the same formats such as block size, number of p-frames, etc. It should be possible to make it lossless -- consider just duplicating B as C, right?
– apoliver
Dec 22 '18 at 23:42
Thanks. But B and C have the same formats such as block size, number of p-frames, etc. It should be possible to make it lossless -- consider just duplicating B as C, right?
– apoliver
Dec 22 '18 at 23:42
By simply copying the video to a new container, yes. By transcoding, no. Ffmpeg supports copying using
-c:v copy– Mokubai♦
Dec 22 '18 at 23:47
By simply copying the video to a new container, yes. By transcoding, no. Ffmpeg supports copying using
-c:v copy– Mokubai♦
Dec 22 '18 at 23:47
Thanks. But my goal is not just copying. I'd like to learn which factors lead to this loss in the second stage and I want to avoid such second quality loss when I use other different codecs.
– apoliver
Dec 23 '18 at 0:49
Thanks. But my goal is not just copying. I'd like to learn which factors lead to this loss in the second stage and I want to avoid such second quality loss when I use other different codecs.
– apoliver
Dec 23 '18 at 0:49
BTW, by copying the video to a new container,
-c:v copy, do you mean that, say copy a video from H.264 to MPEG4 Part2, the format can still be changed to accommodate MPEG4 Part2 but no information loss? Thanks. Sorry that I am new to video compression... I guess the answer is no because I need to specify -c:v mpeg4 ? or I just need to name the output as .mp4 ?– apoliver
Dec 26 '18 at 16:57
BTW, by copying the video to a new container,
-c:v copy, do you mean that, say copy a video from H.264 to MPEG4 Part2, the format can still be changed to accommodate MPEG4 Part2 but no information loss? Thanks. Sorry that I am new to video compression... I guess the answer is no because I need to specify -c:v mpeg4 ? or I just need to name the output as .mp4 ?– apoliver
Dec 26 '18 at 16:57
|
show 2 more comments
1 Answer
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Your procedure is like:
- (source) A → B (result)
- (source) B → C (result)
Lossy encoding produces video that is different from its source, so frames of B are different than frames of A. This means the two sources in the above procedure are different.
I thought B and C have the same format and thus should have the same file size? Why not?
Because they are produced from different source videos.
how can I resolve it to make sure no information loss in the second transcoding process?
- Use lossless encoding
- or do not transcode more than once.
answered Dec 23 '18 at 7:06
Kamil MaciorowskiKamil Maciorowski
25.8k155578
Thanks. I described the actual issue/reason leading my this question in another question transcode-loss-information. Could you take a look?
– apoliver
Dec 25 '18 at 22:11
add a comment |
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1 Answer
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1 Answer
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active
oldest
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oldest
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oldest
votes
Your procedure is like:
- (source) A → B (result)
- (source) B → C (result)
Lossy encoding produces video that is different from its source, so frames of B are different than frames of A. This means the two sources in the above procedure are different.
I thought B and C have the same format and thus should have the same file size? Why not?
Because they are produced from different source videos.
how can I resolve it to make sure no information loss in the second transcoding process?
- Use lossless encoding
- or do not transcode more than once.
answered Dec 23 '18 at 7:06
Kamil MaciorowskiKamil Maciorowski
25.8k155578
Thanks. I described the actual issue/reason leading my this question in another question transcode-loss-information. Could you take a look?
– apoliver
Dec 25 '18 at 22:11
add a comment |
Your procedure is like:
- (source) A → B (result)
- (source) B → C (result)
Lossy encoding produces video that is different from its source, so frames of B are different than frames of A. This means the two sources in the above procedure are different.
I thought B and C have the same format and thus should have the same file size? Why not?
Because they are produced from different source videos.
how can I resolve it to make sure no information loss in the second transcoding process?
- Use lossless encoding
- or do not transcode more than once.
answered Dec 23 '18 at 7:06
Kamil MaciorowskiKamil Maciorowski
25.8k155578
Thanks. I described the actual issue/reason leading my this question in another question transcode-loss-information. Could you take a look?
– apoliver
Dec 25 '18 at 22:11
add a comment |
Your procedure is like:
- (source) A → B (result)
- (source) B → C (result)
Lossy encoding produces video that is different from its source, so frames of B are different than frames of A. This means the two sources in the above procedure are different.
I thought B and C have the same format and thus should have the same file size? Why not?
Because they are produced from different source videos.
how can I resolve it to make sure no information loss in the second transcoding process?
- Use lossless encoding
- or do not transcode more than once.
answered Dec 23 '18 at 7:06
Kamil MaciorowskiKamil Maciorowski
25.8k155578
Your procedure is like:
- (source) A → B (result)
- (source) B → C (result)
Lossy encoding produces video that is different from its source, so frames of B are different than frames of A. This means the two sources in the above procedure are different.
I thought B and C have the same format and thus should have the same file size? Why not?
Because they are produced from different source videos.
how can I resolve it to make sure no information loss in the second transcoding process?
- Use lossless encoding
- or do not transcode more than once.
answered Dec 23 '18 at 7:06
Kamil MaciorowskiKamil Maciorowski
25.8k155578
answered Dec 23 '18 at 7:06
Kamil MaciorowskiKamil Maciorowski
25.8k155578
answered Dec 23 '18 at 7:06
Kamil MaciorowskiKamil Maciorowski
25.8k155578
answered Dec 23 '18 at 7:06
Kamil MaciorowskiKamil Maciorowski
25.8k155578
25.8k155578
Thanks. I described the actual issue/reason leading my this question in another question transcode-loss-information. Could you take a look?
– apoliver
Dec 25 '18 at 22:11
add a comment |
Thanks. I described the actual issue/reason leading my this question in another question transcode-loss-information. Could you take a look?
– apoliver
Dec 25 '18 at 22:11
Thanks. I described the actual issue/reason leading my this question in another question transcode-loss-information. Could you take a look?
– apoliver
Dec 25 '18 at 22:11
Thanks. I described the actual issue/reason leading my this question in another question transcode-loss-information. Could you take a look?
– apoliver
Dec 25 '18 at 22:11
add a comment |
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2
Transcoding always looses data. Video encoding is lossy.
– Mokubai♦
Dec 22 '18 at 22:34
Thanks. But B and C have the same formats such as block size, number of p-frames, etc. It should be possible to make it lossless -- consider just duplicating B as C, right?
– apoliver
Dec 22 '18 at 23:42
By simply copying the video to a new container, yes. By transcoding, no. Ffmpeg supports copying using
-c:v copy– Mokubai♦
Dec 22 '18 at 23:47
Thanks. But my goal is not just copying. I'd like to learn which factors lead to this loss in the second stage and I want to avoid such second quality loss when I use other different codecs.
– apoliver
Dec 23 '18 at 0:49
BTW, by copying the video to a new container,
-c:v copy, do you mean that, say copy a video from H.264 to MPEG4 Part2, the format can still be changed to accommodate MPEG4 Part2 but no information loss? Thanks. Sorry that I am new to video compression... I guess the answer is no because I need to specify-c:v mpeg4? or I just need to name the output as .mp4 ?– apoliver
Dec 26 '18 at 16:57