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• How to read any frame while having frame number using ffmpeg av_seek_frame()

  13 novembre 2024, par Parwez Akhtar

  int64_t timeBase;
timeBase = (int64_t(pavStrm-> time_base.num) * AV_TIME_BASE) / int64_t(pavStrm->time_base.den);
int64_t seekTarget = int64_t(iFrameNumber) * timeBase;
av_seek_frame(fmt_ctx, -1, seekTarget, AVSEEK_FLAG_FRAME);


  



  here I want to read next 5 frame after iFrameNumebr

  



  for(int iCnt = 0; iCnt <= 4; iCnt++)
{
    iRet = av_read_frame(fmt_ctx, &pkt);
        do 
        {
            ret = decode_packet(&got_frame, 0);
            if (ret < 0)
                break;
            pkt.data += ret;
            pkt.size -= ret;

        }while (pkt.size > 0);
    av_free_packet(&pkt);
}

static int decode_packet(int *got_frame, int cached)
{
int ret = 0;
int decoded = pkt.size;
*got_frame = 0;

if (pkt.stream_index == video_stream_idx)
{
    /* decode video frame */
    ret = avcodec_decode_video2(video_dec_ctx, frame, got_frame, &pkt);
}


  



  when i am using AVSEEK_FLAG_BACKWARD its return 5 packet and 5 frame first two is blank but correct.

  



  when i am using AVSEEK_FLAG_FRAME its return 5 packet and 3 frame which are not first 3 frame its return specific frame from video.

  



  for any iFrameNumber

  



  so please help me how to get frame while having frame number and what is exact value of seektarget 3rd param of av_seek_frame()

  



  also I have problem while converting frame to rgb24 format

  


• iOS Libavcodec - Trim and convert a video

  14 juillet 2015, par AnujAroshA

  In my iOS project, I am trying to take an .mp4 video file, cut out a small clip in the middle of the file, and convert the output to .mov file. I am using libavcodec to do this.

  I built the FFmpeg libraries for iOS using this script and added to my project.

  The code I am using to trim and convert the video file is this.

  The issues with final output of the file are :

  1. When I copy the output from the iPhone to my mac, the video meta data for duration and video dimensions are blank. If I do the same for the original, I get the video length and dimensions correctly. I must not be creating the video meta data on the new video correctly.

  2. The frame rate on the outputted video appears to be wrong. I expect to see e.g. 250 frames over 10 seconds (25fps), but instead I see 250 frames over 4 seconds, then only the last frame for the remaining 6 seconds.

  3. The code should seek to 100s in the video before starting trimming. Instead, the code appears to crop the video starting at the beginning.

• FFMPEG, itsoffset with overlay command

  9 janvier 2014, par G.T.

  I managed to overlay two videos one by another with the overlay command and use a nullsrc command to play both video till both of them ended with the following command :

  ./ffmpeg -i first.MOV -i second.MOV -filter_complex "nullsrc=size=1280x400:duration=30[bg];[0]scale=640:-1,pad=1280:400[first];[bg][first]overlay=0:0[base];[1]scale=640:-1[second];[base][second]overlay=640:0" output.mp4

  Now what I wanted to do is to delay one of the overlay till the other one finishes. For this as far as I know the command is itsoffset, so I modified to use this :

  ./ffmpeg -i first.MOV -itsoffset 5 -i second.MOV -filter_complex "nullsrc=size=1280x400:duration=30[bg];[0]scale=640:-1,pad=1280:400[first];[bg][first]overlay=0:0[base];[1]scale=640:-1[second];[base][second]overlay=640:0" output.mp4

  Now my only problem with this is that I want to show the first frame of the delayed video till it starts... And even though somewhere I read that this should do it, it won't. It leaves it blank till the input starts.

  Any idea how could I add the first frame of second video till the itsoffset starts the video ?