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• ffmpeg api alternate transcoding and remuxing for same file

  21 juin 2022, par Alexandre Novius

  Context

  


  Hello !

  


  I'm currently working on the development of a small library allowing to cut an h.264 video on any frame, but without re-encoding (transcoding) the whole video. The idea is to re-encode only the GOP on which we want to cut, and to rewrite (remux) directly the others GOP.

  


  The avcut project (https://github.com/anyc/avcut) allows to do that, but requires a systematic decoding of each package, and seems to not work with the recent versions of ffmpeg from the tests I could do and from the recent feedbacks in the github issues.

  


  As a beginner, I started from the code examples provided in the ffmpeg documentation, in particular : transcoding.c and remuxing.c.

  


  Problem encountered

  


  The problem I'm having is that I can't get both transcoding and remuxing to work properly at the same time. In particular, depending on the method I use to initialize the AVCodecParameters of the output video stream, transcoding works, or remuxing works :

  


  

  • avcodec_parameters_copy works well for remuxing

  


  • avcodec_parameters_from_context works well for transcoding

  


  


  In case I choose avcodec_parameters_from_context, the transcoded GOP are correctly read by my video player (parole), but the remuxed packets are not read, and ffprobe does not show/detect them.

  


  In case I choose avcodec_parameters_from_context, the remuxing GOP are correctly read by my video player, but the transcoding key_frame are bugged (I have the impression that the b-frame and p-frame are ok), and ffprobe -i return an error about the NAL of the key-frames :

  


  [h264 @ 0x55ec8a079300] sps_id 32 out of range
[h264 @ 0x55ec8a079300] Invalid NAL unit size (1677727148 > 735).
[h264 @ 0x55ec8a079300] missing picture in access unit with size 744


  


  I suspect that the problem is related to the extradata of the packets. Through some experiments on the different attributes of the output AVCodecParameters, it seems that it is the extradata and extradata_size attributes that are responsible for the functioning of one method or the other.

  


  Version

  


  ffmpeg development branch retrieved on 2022-05-17 from https://github.com/FFmpeg/FFmpeg.

  


  Compiled with --enable-libx264 --enable-gpl --enable-decoder=png --enable-encoder=png

  


  Code

  


  My code is written in c++ and is based on two classes : a class defining the parameters and methods on the input file (InputContexts) and a class defining them for the output file (OutputContexts). The code of these two classes is defined in the following files :

  


  

  • contexts.h

  


  • contexts.cpp

  


  


  The code normally involved in the problem is the following :

  


  

  • stream initialization

  


  


  int OutputContexts::init(const char* out_filename, InputContexts* input_contexts){
    int ret;
    int stream_index = 0;

    avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, out_filename);
    if (!ofmt_ctx) {
        fprintf(stderr, "Could not create output context\n");
        ret = AVERROR_UNKNOWN;
        return ret;
    }

    av_dump_format(ofmt_ctx, 0, out_filename, 1);
 
    encoders.resize(input_contexts->ifmt_ctx->nb_streams, nullptr);
    codecs.resize(input_contexts->ifmt_ctx->nb_streams, nullptr);
  
    // stream mapping
    for (int i = 0; i < input_contexts->ifmt_ctx->nb_streams; i++) {
        AVStream *out_stream;
        AVStream *in_stream = input_contexts->ifmt_ctx->streams[i];
        AVCodecContext* decoder_ctx = input_contexts->decoders[i];
 
        // add new stream to output context
        out_stream = avformat_new_stream(ofmt_ctx, NULL);
        if (!out_stream) {
            fprintf(stderr, "Failed allocating output stream\n");
            ret = AVERROR_UNKNOWN;
            return ret;
        }

        // from avcut blog
        av_dict_copy(&out_stream->metadata, in_stream->metadata, 0);

        out_stream->time_base = in_stream->time_base;

        // encoder
        if (decoder_ctx->codec_type == AVMEDIA_TYPE_VIDEO){
            ret = prepare_encoder_video(i, input_contexts);
            if (ret < 0){
                fprintf(stderr, "Error while preparing encoder for stream #%u\n", i);
                return ret;
            }

            // from avcut
            out_stream->sample_aspect_ratio = in_stream->sample_aspect_ratio;

            // works well for remuxing
            ret = avcodec_parameters_copy(out_stream->codecpar, in_stream->codecpar);
            if (ret < 0) {
                fprintf(stderr, "Failed to copy codec parameters\n");
                return ret;
            }

            // works well for transcoding
            // ret = avcodec_parameters_from_context(out_stream->codecpar, encoders[i]);
            // if (ret < 0) {
            //     av_log(NULL, AV_LOG_ERROR, "Failed to copy encoder parameters to output stream #%u\n", i);
            //     return ret;
            // }

        } else if (decoder_ctx->codec_type == AVMEDIA_TYPE_AUDIO) {
            ...
        } else {
            ...
        }

        // TODO useful ???
        // set current stream position to 0
        // out_stream->codecpar->codec_tag = 0;
    }

    // opening output file in write mode with the ouput context
    if (!(ofmt_ctx->oformat->flags & AVFMT_NOFILE)) {
        ret = avio_open(&ofmt_ctx->pb, out_filename, AVIO_FLAG_WRITE);
        if (ret < 0) {
            fprintf(stderr, "Could not open output file '%s'", out_filename);
            return ret;
        }
    }
 
    // write headers from output context in output file
    ret = avformat_write_header(ofmt_ctx, NULL);
    if (ret < 0) {
        fprintf(stderr, "Error occurred when opening output file\n");
        return ret;
    }

    return ret;
}


  


  

  • AVCodecContext initialization for encoder

  


  


  int OutputContexts::prepare_encoder_video(int stream_index, InputContexts* input_contexts){
    int ret;
    const AVCodec* encoder;
    AVCodecContext* decoder_ctx = input_contexts->decoders[stream_index];
    AVCodecContext* encoder_ctx;

    if (video_index >= 0){
        fprintf(stderr, "Impossible to mark stream #%u as video, stream #%u is already registered as video stream.\n", 
                stream_index, video_index);
        return -1; //TODO change this value for correct error code
    }
    video_index = stream_index;

    if(decoder_ctx->codec_id == AV_CODEC_ID_H264){
        encoder = avcodec_find_encoder_by_name("libx264");
        if (!encoder) {
            av_log(NULL, AV_LOG_FATAL, "Encoder libx264 not found\n");
            return AVERROR_INVALIDDATA;
        }
        fmt::print("Encoder libx264 will be used for stream {}.\n", stream_index);
    } else {
        std::string s = fmt::format("No video encoder found for the given codec_id: {}\n", avcodec_get_name(decoder_ctx->codec_id));
        av_log(NULL, AV_LOG_FATAL, s.c_str());
        return AVERROR_INVALIDDATA;
    }
    
    encoder_ctx = avcodec_alloc_context3(encoder);
    if (!encoder_ctx) {
        av_log(NULL, AV_LOG_FATAL, "Failed to allocate the encoder context\n");
        return AVERROR(ENOMEM);
    }

    // from avcut
    encoder_ctx->time_base = decoder_ctx->time_base;
    encoder_ctx->ticks_per_frame = decoder_ctx->ticks_per_frame;
    encoder_ctx->delay = decoder_ctx->delay;
    encoder_ctx->width = decoder_ctx->width;
    encoder_ctx->height = decoder_ctx->height;
    encoder_ctx->pix_fmt = decoder_ctx->pix_fmt;
    encoder_ctx->sample_aspect_ratio = decoder_ctx->sample_aspect_ratio;
    encoder_ctx->color_primaries = decoder_ctx->color_primaries;
    encoder_ctx->color_trc = decoder_ctx->color_trc;
    encoder_ctx->colorspace = decoder_ctx->colorspace;
    encoder_ctx->color_range = decoder_ctx->color_range;
    encoder_ctx->chroma_sample_location = decoder_ctx->chroma_sample_location;
    encoder_ctx->profile = decoder_ctx->profile;
    encoder_ctx->level = decoder_ctx->level;

    encoder_ctx->thread_count = 1; // spawning more threads causes avcodec_close to free threads multiple times
    encoder_ctx->codec_tag = 0;
    
    // correct values ???
    encoder_ctx->qmin = 16;
    encoder_ctx->qmax = 26;
    encoder_ctx->max_qdiff = 4;
    // end from avcut

    // according to avcut, should not be set
    // if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER){
    //     encoder_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
    // }

    ret = avcodec_open2(encoder_ctx, encoder, NULL);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "Cannot open video encoder for stream #%u\n", stream_index);
        return ret;
    }
    
    codecs[stream_index] = encoder;
    encoders[stream_index] = encoder_ctx;

    return ret;
}


  


  Example

  


  To illustrate my problem, I provide here a test code using the two classes that alternates between transcoding and remuxing at each key-frame encountered in the file using my classes.

  


  

  • trans_remux.cpp

  


  


  To compile the code :

  


  g++ -o trans_remux trans_remux.cpp contexts.cpp -D__STDC_CONSTANT_MACROS `pkg-config --libs libavfilter` -lfmt -g


  


  Currently the code is using avcodec_parameters_copy (contexts.cpp:333), so it works well for remuxing. If you want to test the version with avcodec_parameters_from_context, pls comment from line 333 to 337 in contexts.cpp and uncomment from line 340 to 344 and recompile.

  


• FFMpeg crop a portrait (vertical) video square 1:1

  1er avril 2022, par hugger

  SOLVED... It was a UI issue... Not an FFpeg issue.

  


  I am new to FFMpeg. I am stuck on cropping a portrait video taken from a portrait device square.

  


  I would like my video output to be 1080x1080.

  


  First, I tried this.

  


  FFmpegKit.execute(`-y -i ${media.path} -vf "crop=1080:1080:exact=1" ${path}`)


  


  As I hoped, this worked for photos. (but strangely rotates the photo) - looking into that...

  


  BUT, for videos it does not work. instead it turns the video landscape.

  


  I then tried to add scale :

  


  FFmpegKit.execute(`-y -i ${media.path} -vf "crop=1080:1080:exact=1, scale=1080:1080" ${path}`)


  


  But this left me with the same result.

  


  Here are the console logs for some more information :

  


   LOG  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'file:///private/var/mobile/Containers/Data/Application/71E462FC-4824-41FE-B28D-57AF7B6078C3/tmp/ReactNative/329ACC6F-42B6-4B12-A289-889DADE1BC3A.mov':
 LOG    Metadata:
 LOG      major_brand     :
 LOG  qt
 LOG  
 LOG      minor_version   :
 LOG  0
 LOG  
 LOG      compatible_brands:
 LOG  qt
 LOG  
 LOG      creation_time   :
 LOG  2022-04-01T03:41:12.000000Z
 LOG  
 LOG    Duration:
 LOG  00:00:02.35
 LOG  , start:
 LOG  0.000000
 LOG  , bitrate:
 LOG  21200 kb/s
 LOG  
 LOG    Stream #0:0
 LOG  [0x1]
 LOG  (und)
 LOG  : Video: hevc (hvc1 / 0x31637668), yuv420p(tv, bt709), 1080x1920, 21140 kb/s
 LOG  ,
 LOG  59.96 fps,
 LOG  59.94 tbr,
 LOG  600 tbn
 LOG   (default)
 LOG  
 LOG      Metadata:
 LOG        creation_time   :
 LOG  2022-04-01T03:41:13.000000Z
 LOG  
 LOG        handler_name    :
 LOG  Core Media Video
 LOG  
 LOG        vendor_id       :
 LOG  [0][0][0][0]
 LOG  
 LOG        encoder         :
 LOG  HEVC
 LOG  
 LOG    Stream #0:1
 LOG  [0x2]
 LOG  (und)
 LOG  : Audio: aac (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 61 kb/s
 LOG   (default)
 LOG  
 LOG      Metadata:
 LOG        creation_time   :
 LOG  2022-04-01T03:41:13.000000Z
 LOG  
 LOG        handler_name    :
 LOG  Core Media Audio
 LOG  
 LOG        vendor_id       :
 LOG  [0][0][0][0]
 LOG  
 LOG  [hevc @ 0x118ce07d0] The "sub_text_format" option is deprecated: Deprecated, does nothing
 LOG  [aac @ 0x10d30e190] The "sub_text_format" option is deprecated: Deprecated, does nothing
 LOG  Stream mapping:
 LOG    Stream #0:0 -> #0:0
 LOG   (hevc (native) -> mpeg4 (native))
 LOG  
 LOG    Stream #0:1 -> #0:1
 LOG   (aac (native) -> aac (native))
 LOG  
 LOG  Press [q] to stop, [?] for help
 LOG  Output #0, mp4, to '/var/mobile/Containers/Data/Application/71E462FC-4824-41FE-B28D-57AF7B6078C3/Documents/after.mp4':
 LOG    Metadata:
 LOG      major_brand     :
 LOG  qt
 LOG  
 LOG      minor_version   :
 LOG  0
 LOG  
 LOG      compatible_brands:
 LOG  qt
 LOG  
 LOG      encoder         :
 LOG  Lavf59.10.100
 LOG  
 LOG    Stream #0:0
 LOG  (und)
 LOG  : Video: mpeg4 (mp4v / 0x7634706D), yuv420p(tv, bt709, progressive), 1080x1080, q=2-31, 10000 kb/s
 LOG  ,
 LOG  59.94 fps,
 LOG  60k tbn
 LOG   (default)
 LOG  
 LOG      Metadata:
 LOG        creation_time   :
 LOG  2022-04-01T03:41:13.000000Z
 LOG  
 LOG        handler_name    :
 LOG  Core Media Video
 LOG  
 LOG        vendor_id       :
 LOG  [0][0][0][0]
 LOG  
 LOG        encoder         :
 LOG  Lavc59.15.102 mpeg4
 LOG  
 LOG      Side data:
 LOG  
 LOG  cpb:
 LOG  bitrate max/min/avg: 0/0/10000000 buffer size: 0
 LOG  vbv_delay: N/A
 LOG  
 LOG    Stream #0:1
 LOG  (und)
 LOG  : Audio: aac (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 69 kb/s
 LOG   (default)
 LOG  
 LOG      Metadata:
 LOG        creation_time   :
 LOG  2022-04-01T03:41:13.000000Z
 LOG  
 LOG        handler_name    :
 LOG  Core Media Audio
 LOG  
 LOG        vendor_id       :
 LOG  [0][0][0][0]
 LOG  
 LOG        encoder         :
 LOG  Lavc59.15.102 aac
 LOG  
 LOG  frame=    1 fps=0.0 q=3.6 size=       0kB time=00:00:01.06 bitrate=   0.3kbits/s speed=9.23x
 LOG  frame=   47 fps=0.0 q=2.0 size=     768kB time=00:00:01.85 bitrate=3390.0kbits/s speed=3.01x
 LOG  frame=   95 fps= 81 q=2.2 size=    1792kB time=00:00:02.32 bitrate=6313.3kbits/s speed=1.99x
 LOG  frame=  129 fps= 77 q=2.5 size=    2560kB time=00:00:02.32 bitrate=9018.9kbits/s speed=1.39x
 LOG  frame=  139 fps= 78 q=2.6 Lsize=    2953kB time=00:00:02.38 bitrate=10124.6kbits/s speed=1.34x
 LOG  video:2929kB audio:20kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead:
 LOG  0.136336%
 LOG  
 LOG  [aac @ 0x112820f50] Qavg: 113.412
 LOG  COMPLETED
 LOG  {}


  


  This is the result, when i replace
-i {media} with
-f lavfi -i smptebars=r=60000/1001:s=1080x1920:d=1

  


  

  


  ALMOST but not 1:1...

  


  I have not had any luck online trying to find a solution for this so I have decided to post on here.

  


  I hope I can get some guidance here !

  


  Cheers.

  


• ffmpeg how to concat and COMPRESS at the same time ? [closed]

  17 juin 2022, par Alex Nox

  Concat command :

  


  ffmpeg -f concat -safe 0 -i list.txt -c copy output.mp4


  


  Content of list.txt

  


  file '2022-03-26-1.mp4'

file '2022-03-26-2.mp4'


  


  The following above seems working, but I want to compress files at the same time, so I type :

  


  ffmpeg concat -an -i list.txt -crf 23 -c:v libx264 out.mp4


  


  But it doesn't work ? Why ?