[Libav-user] Problem Generating B-Frames Using libavcodec/libx264

[Francesco Damato]

Hi Robert,

i have your same goal, also I am writing a an application that encodes
incoming video in H.264 using libavcodec and libx264. I don't know the
solution for yuor problem, because i do not know how to encode.
i have a avi or mp4 file as input. The *avcodec_encode_video2* function
takes input raw video data from frame, so i demux my file and i obtain a
raw video file; now i want encode it, so how i can open the raw file, read
the raw frames and encode them into h264?? Is this the right wat yo encode
in H.264? There are other solutions?? How do you encode?? Can you help me,
please??

Thanks in advance.

Regards


2013/10/21 Robert Schmidt <rob.schmidt86 at outlook.com>

> Hello all,
>
> I am writing a an application that encodes incoming video in H.264 using
> libavcodec and libx264.  However, I noticed that the output data was much
> larger than I expected.  When I examined the output, I discovered that the
> encoder was only producing I- and P-frames and never producing B-frames.
>
> I created a standalone utility in an attempt to isolate my encoding logic
> and determine what I am doing wrong.  The utility reads in H.264 video from
> a file stored using the ITU H.264 Annex B format, decodes it, re-encodes
> it, and writes the resulting packets to another file in the Annex B
> format.  Like my application, the test utility fails to generate any
> B-frames.
>
> I ran the input file through ffmpeg using the same settings that I was
> providing in my utility and found that ffmpeg does produce B-frames.  I
> have been trying to determine what I am doing differently than ffmpeg, but
> I have not been able to figure it out yet.  I'm hoping that perhaps someone
> on this list can spot my oversight.
>
> I use the following command line with ffmpeg:
>
>     $ ffmpeg -v debug -i ~/annexb.264 -codec:v libx264 -preset superfast
> -g 30 -f h264 ./out.264
>
> As far as I can tell, ffmpeg should simply be using the "superfast"
> libx264 preset and a group of pictures setting of 30 frames.  Beyond that,
> it should be using the defaults.
>
> My code to set up the encoder looks like the following:
>
> static AVStream *add_video_stream(AVFormatContext *output_ctx, AVCodec
> **output_codec, enum AVCodecID codec_id)
> {
>     *output_codec = avcodec_find_encoder(codec_id);
>     if (*output_codec == NULL) {
>         printf("Could not find encoder for '%s' (%d)\n",
> avcodec_get_name(codec_id), codec_id);
>         return NULL;
>     }
>
>     AVStream *output_stream = avformat_new_stream(output_ctx,
> *output_codec);
>     if (output_stream == NULL) {
>         printf("Could not create video stream.\n");
>         return NULL;
>     }
>     output_stream->id = output_ctx->nb_streams - 1;
>     AVCodecContext *codec_ctx = output_stream->codec;
>
>     avcodec_get_context_defaults3(codec_ctx, *output_codec);
>
>     codec_ctx->width = 1280;
>     codec_ctx->height = 720;
>
>     codec_ctx->time_base.den = 15000;
>     codec_ctx->time_base.num = 1001;
>
> /*    codec_ctx->gop_size = 30;*/
>     codec_ctx->pix_fmt = AV_PIX_FMT_YUVJ420P;
>
>     // try to force B-frame output
> /*    codec_ctx->max_b_frames = 3;*/
> /*    codec_ctx->b_frame_strategy = 2;*/
>
>     output_stream->sample_aspect_ratio.num = 1;
>     output_stream->sample_aspect_ratio.den = 1;
>
>     codec_ctx->sample_aspect_ratio.num = 1;
>     codec_ctx->sample_aspect_ratio.den = 1;
>
>     codec_ctx->chroma_sample_location = AVCHROMA_LOC_LEFT;
>
>     codec_ctx->bits_per_raw_sample = 8;
>
>     if ((output_ctx->oformat->flags & AVFMT_GLOBALHEADER) != 0) {
>         codec_ctx->flags |= CODEC_FLAG_GLOBAL_HEADER;
>     }
>
>     return output_stream;
> }
>
>
> int main(int argc, char **argv)
> {
>     // ... open input file
>
>     avformat_alloc_output_context2(&output_ctx, NULL, "h264", output_path);
>     if (output_ctx == NULL) {
>         fprintf(stderr, "Unable to allocate output context.\n");
>         return 1;
>     }
>
>     AVCodec *output_codec = NULL;
>     output_stream = add_video_stream(output_ctx, &output_codec,
> output_ctx->oformat->video_codec);
>     if (output_stream == NULL) {
>         fprintf(stderr, "Error adding video stream to output context.\n");
>         return 1;
>     }
>     encode_ctx = output_stream->codec;
>
>     // seems to have no effect
> #if 0
>     if (decode_ctx->extradata_size != 0) {
>         size_t extradata_size = decode_ctx->extradata_size;
>         printf("extradata_size: %zu\n", extradata_size);
>         encode_ctx->extradata = av_mallocz(extradata_size +
> FF_INPUT_BUFFER_PADDING_SIZE);
>         memcpy(encode_ctx->extradata, decode_ctx->extradata,
> extradata_size);
>         encode_ctx->extradata_size = extradata_size;
>     }
> #endif // 0
>
>     AVDictionary *opts = NULL;
>     av_dict_set(&opts, "preset", "superfast", 0);
>     // av_dict_set(&opts, "threads", "auto", 0); // seems to have no effect
>
>     ret = avcodec_open2(encode_ctx, output_codec, &opts);
>     if (ret < 0) {
>         fprintf(stderr, "Unable to open output video cocec: %s\n",
> av_err2str(ret));
>         return 1;
>     }
>
>     // ... decoding/encoding loop, clean up, etc.
>
>     return 0;
> }
>
> I have tried manually specifying the B-frame parameters in the
> AVCodecContext structure to no avail.
>
> I've also tried debugging both my utility and ffmpeg under gdb so that I
> can compare the values of the AVCodecContext, X264Context, and AVStream
> structures.   I have tried to make sure they are identical, but I still am
> not getting any B-frames.
>
> For a while I thought perhaps the issue was that I was mishandling
> timestamps, so I replicated ffmpeg's processing chain and output timestamp
> debugging information similar to what ffmpeg produces.  My debugging output
> appears identical to ffmpeg's.
>
> Does anyone have any ideas as to what I may be doing wrong?  I asked the
> same question on StackOverflow last week (
> http://stackoverflow.com/q/19456745/2895838) where I also included some
> of the logging output from both ffmpeg and my test utility.  I've omitted
> that here in the interest of brevity.  I also thought that the entire
> source code for the test utility would be too long for an e-mail, but I'm
> happy to provide more if that is helpful.
>
> For what it's worth, I'm currently using ffmpeg 1.2 and its libraries.
>
> Any assistance is greatly appreciated.  I've been banging my head against
> this one for a while now.
>
> Thanks in advance.
>
> Rob
> _______________________________________________
> Libav-user mailing list
> Libav-user at ffmpeg.org
> http://ffmpeg.org/mailman/listinfo/libav-user
>



-- 
Francesco Damato
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