Re: [FFmpeg-user] essence MD5 for still images
2018-01-09 22:25 GMT+01:00 *** : > On the same subject Appears to be a different subject, but most of all, please remember not to top-post on this mailing list. > when calculating the MD5 of an audio WAV file ffmpeg > defaults to 16 bit. No, ffmpeg does not default to "16 bit" or a particular encoder, some muxers default to pcm_s16le for audio if you do not specify a particular encoder. > If the input is 24 bit it is my understanding that > it needs to be explicitly reflected in the command > as -c:a pcm_s24le otherwise the resulting MD5 will > not be accurate. So, yes, if you need accurate md5 for 24 bit input, you have to specify a 24 bit encoder. > Are there comparable variations in the way ffmpeg > processes still image files of different formats, bit > depths, etc., that need to be accounted for in the > command that is used? Typically not: The rawvideo (and the wrapped_avframe) encoder accepts any pix_fmt while the pcm_s16le encoder only accepts s16 input, the pcm_s24le encoder only supports s32 (sic!). Carl Eugen ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
Re: [FFmpeg-user] essence MD5 for still images
On the same subject, when calculating the MD5 of an audio WAV file ffmpeg defaults to 16 bit. If the input is 24 bit it is my understanding that it needs to be explicitly reflected in the command as -c:a pcm_s24le otherwise the resulting MD5 will not be accurate. Are there comparable variations in the way ffmpeg processes still image files of different formats, bit depths, etc., that need to be accounted for in the command that is used? On Sat, Jan 6, 2018 at 4:31 PM, Carl Eugen Hoyos wrote: > 2018-01-06 20:38 GMT+01:00 *** : > > > Somewhere I discovered that ffmpeg will create essence > > MD5s for supported still image formats. > > And audio and video. > (From FFmpeg's pov, an image format is a video format.) > > > I began using the following command to verify that > > the image essence did not change in photos after > > their IPTC metadata is revised. > > > Because there is no documentation of such a use case > > on the ffmpeg site nor anywhere else on the web I have > > begun to doubt that this is a valid use of ffmpeg or this > > command. > > Different possibilities exist within FFmpeg to calculate > checksums, the FFmpeg regression tests are a usage > example. > > > Is anyone else doing this? > > Many people are. > > > Even if you aren’t I would appreciate any comments or > > observations that you care to share. > > > > ffmpeg -i INPUT -map 0:v -f md5 OUTPUT.md5 > > This command line will calculate the md5sum of the first > video stream in the input file. > You may want to look at the framemd5 muxer for other > use-cases, other algorithms also exist. > > Carl Eugen > ___ > ffmpeg-user mailing list > ffmpeg-user@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-user > > To unsubscribe, visit link above, or email > ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe". ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
Re: [FFmpeg-user] essence MD5 for still images
2018-01-06 20:38 GMT+01:00 *** : > Somewhere I discovered that ffmpeg will create essence > MD5s for supported still image formats. And audio and video. (From FFmpeg's pov, an image format is a video format.) > I began using the following command to verify that > the image essence did not change in photos after > their IPTC metadata is revised. > Because there is no documentation of such a use case > on the ffmpeg site nor anywhere else on the web I have > begun to doubt that this is a valid use of ffmpeg or this > command. Different possibilities exist within FFmpeg to calculate checksums, the FFmpeg regression tests are a usage example. > Is anyone else doing this? Many people are. > Even if you aren’t I would appreciate any comments or > observations that you care to share. > > ffmpeg -i INPUT -map 0:v -f md5 OUTPUT.md5 This command line will calculate the md5sum of the first video stream in the input file. You may want to look at the framemd5 muxer for other use-cases, other algorithms also exist. Carl Eugen ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
[FFmpeg-user] essence MD5 for still images
Hello Somewhere I discovered that ffmpeg will create essence MD5s for supported still image formats. I began using the following command to verify that the image essence did not change in photos after their IPTC metadata is revised. Because there is no documentation of such a use case on the ffmpeg site nor anywhere else on the web I have begun to doubt that this is a valid use of ffmpeg or this command. Is anyone else doing this? Even if you aren’t I would appreciate any comments or observations that you care to share. ffmpeg -i INPUT -map 0:v -f md5 OUTPUT.md5 Thank you Kevin Irelan ___ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
