Proof of Concept

Here is the list of the commands used for transcoding a sequence of 16-bit DPX files, using the FFV1 codec, into a Matroska container, and then to transcode back the generated file to a sequence of 16-bit DPX files.

I wish to acknowledge the help provided by Kieran O’Leary from the Irish Film Archive.

Note: For the presentation done at The Reel Thing XXXVIII the HEAD version of FFmpeg was needed, because the capability to handle RGB with 16 bit per channel (planar gbrp16 and packed rgb48) has just been implemented into FFV1, and is currently tested. In the near future any official release will work.

Set the desktop as working space in order to find the generated files easier

cd ~/Desktop

Compute MD5 hash values for the original DPX files

ffmpeg -i ORIGINAL/original_%06d.dpx -f framemd5 md5_original.txt

Command syntax

ffmpeg

starts the command

-i ORIGINAL/original_%06d.dpx

path, name and extension of the input files
The regex %06d matches six digits long numbers, possibly with leading zeroes. This allows to read in ascending order, one image after the other, the full sequence inside the folder. The filename must, of course, match the naming convention actually used.

-f framemd5

The library framemd5 calculates an MD5 checksum of the image content of each frame.

md5_original.txt

path, name and extension of the output file

Transcode the RGB content inside the DPX file, using FFV1, into Matroska

ffmpeg -i ORIGINAL/original_%06d.dpx -c:v ffv1 -level 3 -strict -2 test.mkv

Command syntax

ffmpeg

starts the command

-i ORIGINAL/original_%06d.dpx

path, name and extension of the input files
The regex %06d matches six digits long numbers, possibly with leading zeroes. This allows to read in ascending order, one image after the other, the full sequence inside the folder. The filename must, of course, match the naming convention actually used.

-c:v ffv1

The video codec FFV1 is chosen.

-level 3

The version 3 of FFV1 is selected.

-strict -2

For the presentation done at The Reel Thing XXXVIII this debugging parameter was needed, because the capability to handle RGB with 16 bit per channel (planar gbrp16 and packed rgb48) has just been implemented into FFV1, and is currently tested. As soon as the next official version of FFmpeg has been released, this parameter will not longer be needed.

test.mkv

path, name and extension of the output file

Create a folder for the new DPX

mkdir COPY

Transcode the content of the Matroska file into new DPX files

ffmpeg -i test.mkv COPY/copy_%06d.dpx

Command syntax

ffmpeg

starts the command

-i test.mkv

path, name and extension of the input files

COPY/copy_%06d.dpx

path, name and extension of the output file

Compute MD5 hash values for the new DPX files

ffmpeg -i COPY/copy_%06d.dpx -f framemd5 md5_copy.txt

ffmpeg

starts the command

-i COPY/copy_%06d.dpx

path, name and extension of the input files

-f framemd5

The library framemd5 calculates an MD5 checksum of the image content of each frame.

md5_copy.txt

path, name and extension of the output file

Compare the MD5 hash values

diff md5_original.txt md5_copy.txt

2018-07-18