On 21-09-2024 04:39, Alan Chen via ffmpeg-user wrote:
I am using ffmpeg.
I use the following command to get all packet info:
ffprobe -print_format json -show_packets -show_streams -show_entries
packet=pts,duration,size,codec_type,pos test.mp4 > test.mp4.info
Then based on each packet info, such as the one below:
{
"codec_type": "video",
"pts": 0,
"duration": 512,
"size": "6419",
"pos": "175"
}
I extract the raw data of the packet from the test.mp4 file, take the above
packet as a example, I extract the data at offset = 175 and size = 6419,
then save the packet into a new file, video_sample0.dat.
I write an app to write all the packets into different audio and video
files, i.e., audio_sample0.dat, audio_sample1.dat, ..., video_sample0.dat,
video_sample1.dat...
Then I use ffprobe with -show_data option to show the raw data of each
packet, then compare the output with my packet files and confirm they are
identical.
After that, I remove some useless packets. Then try to recreate a new MP4
file with the remaining packets.
I take one packet file as a test:
ffmpeg -f m4v -i video_sample0.dat -c copy output.mp4
But get the following error:
ffmpeg version 7.0.2 Copyright (c) 2000-2024 the FFmpeg developers
built with gcc 14.1.0 (Rev3, Built by MSYS2 project)
configuration: --enable-shared
libavutil 59. 8.100 / 59. 8.100
libavcodec 61. 3.100 / 61. 3.100
libavformat 61. 1.100 / 61. 1.100
libavdevice 61. 1.100 / 61. 1.100
libavfilter 10. 1.100 / 10. 1.100
libswscale 8. 1.100 / 8. 1.100
libswresample 5. 1.100 / 5. 1.100
[mpeg4 @ 00628400] time_increment_bits 0 is invalid in relation to the
current bitstream, this is likely caused by a missing VOL header
[mpeg4 @ 00628400] time_increment_bits set to 5 bits, based on
bitstream analysis
[mpeg4 @ 00628400] time_increment_bits 4 is invalid in relation to the
current bitstream, this is likely caused by a missing VOL header
[mpeg4 @ 00628400] time_increment_bits set to 5 bits, based on
bitstream analysis
[mpeg4 @ 00628400] looks like this file was encoded with
(divx4/(old)xvid/opendivx) -> forcing low_delay flag
[m4v @ 003e8d00] Could not find codec parameters for stream 0 (Video:
mpeg4, yuv420p): unspecified size
Consider increasing the value for the 'analyzeduration' (0) and
'probesize' (5000000) options
Input #0, m4v, from 'video_sample0.dat':
Duration: N/A, bitrate: N/A
Stream #0:0: Video: mpeg4, yuv420p, 25 fps, 1200k tbr, 1200k tbn
File 'output.mp4' already exists. Overwrite? [y/N] y
Stream mapping:
Stream #0:0 -> #0:0 (copy)
[mp4 @ 00628400] dimensions not set
[out#0/mp4 @ 0062b380] Could not write header (incorrect codec
parameters ?): Invalid argument
Conversion failed!
So, how to reassemble the raw packet data back to a new MP4 file?
_______________________________________________
Start reading and understanding this:https://www.iso.org/standard/55688.html
It is the first of 32 parts to read in order to understand how MPEG-4
works and how to (re)create it. Unfortunately, this information is not
free (patented) so you'll have to pay to read it.
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