libavformat/libavcodec providing invalid container header

Question

I'm using libavcodec to encode a stream to h264 and libavformat to store it in an mp4. The resulting container has an invalid header that can be played in VLC, but not any other player.

I've found that using the mp4 container and the "mpeg4" codec produces a valid mp4 file, but using libx265 (HEVC) or the libx264 codec produces invalid mp4s.

I can use ffmpeg -i invalid.mp4 -vcodec copy valid.mp4 and I get a file of almost the exact same size, but in a valid container.

Examples of these files are here: Broken file and Repaied file [use the download links in the upper right to examine]

I used a hex editor to see the differences in the headers of the two files and the invalid one is 1 byte smaller than the valid one.

The code I'm using to open the container and codec and to write the header is here:

AVOutputFormat *container_format;
AVFormatContext *container_format_context;
AVStream *video_stream;
int ret;

/* allocate the output media context */
avformat_alloc_output_context2(&container_format_context, NULL, NULL, out_file);
if (!container_format_context) {
    log(INFO, "Unable to determine container format from filename, exiting\n");
    exit(1);
}
else {
    log(INFO, "Using container %s\n", container_format_context->oformat->name);
}

if (!container_format_context) {
    log(ERROR, "Could not build container format context. Encoding failed.");
    exit(1);
}

container_format = container_format_context->oformat;

/* Pull codec based on name */
AVCodec* codec = avcodec_find_encoder_by_name(codec_name);
if (codec == NULL) {
    log(ERROR, "Failed to locate codec \"%s\".",
            codec_name);
    exit(1);
}

/* create stream */
video_stream = NULL;
video_stream = avformat_new_stream(container_format_context, codec);
if (!video_stream) {
    log(ERROR, "Could not allocate encoder stream. Cannot continue.\n");
    exit(1);
}
video_stream->id = container_format_context->nb_streams - 1;

video_stream->time_base = video_stream->codec->time_base = (AVRational) { 1, 25};

av_dump_format(container_format_context, 0, out_file, 1);



/* Retrieve encoding context */
AVCodecContext* avcodec_context = video_stream->codec;
if (avcodec_context == NULL) {
    log(ERROR, "Failed to allocate context for "
            "codec \"%s\".", codec_name);
    exit(1);
}


/* Init context with encoding parameters */
avcodec_context->bit_rate = bitrate;
avcodec_context->width = width;
avcodec_context->height = height;
avcodec_context->gop_size = 10;
avcodec_context->max_b_frames = 1;
avcodec_context->qmax = 31;
avcodec_context->qmin = 2;
avcodec_context->pix_fmt = AV_PIX_FMT_YUV420P;

av_dump_format(container_format_context, 0, out_file, 1);

/* Open codec for use */
if (avcodec_open2(avcodec_context, codec, NULL) < 0) {
    log(ERROR, "Failed to open codec \"%s\".", codec_name);
    exit(1);
}

/* Allocate corresponding frame */
AVFrame* frame = av_frame_alloc();
if (frame == NULL) {
    exit(1);
}

/* Copy necessary data for frame from avcodec_context */
frame->format = avcodec_context->pix_fmt;
frame->width = avcodec_context->width;
frame->height = avcodec_context->height;

/* Allocate actual backing data for frame */
if (av_image_alloc(frame->data, frame->linesize, frame->width,
            frame->height, frame->format, 32) < 0) {
    exit(1);
}

/* open the output file, if the container needs it */
if (!(container_format->flags & AVFMT_NOFILE)) {
    ret = avio_open(&container_format_context->pb, out_file, AVIO_FLAG_WRITE);
    if (ret < 0) {
        log(ERROR, "Error occurred while opening output file: %s\n",
                av_err2str(ret));
        exit(1);
    }
}

/* write the stream header, if needed */
ret = avformat_write_header(container_format_context, NULL);
if (ret < 0) {
    log(ERROR, "Error occurred while writing output file header: %s\n",
                av_err2str(ret));
}

The code to encode a frame is here:

/* Init video packet */
AVPacket packet;
av_init_packet(&packet);

/* Request that encoder allocate data for packet */
packet.data = NULL;
packet.size = 0;

/* Write frame to video */
int got_data;
if (avcodec_encode_video2(avcontext, &packet, frame, &got_data) < 0) {
    log(WARNING, "Error encoding frame #%" PRId64,
            video_struct->next_pts);
    return -1;
}

/* Write corresponding data to file */
if (got_data) {
    if (packet.pts != AV_NOPTS_VALUE) {
        packet.pts = av_rescale_q(packet.pts, video_struct->output_stream->codec->time_base, video_struct->output_stream->time_base);
    }
    if (packet.dts != AV_NOPTS_VALUE) {
        packet.dts = av_rescale_q(packet.dts, video_struct->output_stream->codec->time_base, video_struct->output_stream->time_base);
    }
    write_packet(video_struct, &packet, packet.size);
    av_packet_unref(&packet);
}

And the code to write the packet to the video stream:

static int write_packet(video_struct* video, void* data, int size) {

int ret;

/* use AVStream is not null, otherwise write to output fd */
AVPacket *pkt = (AVPacket*) data;
pkt->stream_index = video->output_stream->index;
ret = av_interleaved_write_frame(video->container_format_context, pkt);
if (ret != 0) {
    return -1;
}

/* Data was written successfully */
return ret;
}

Answer 1

Solved this issue. The problem was that I wasn't assigning global headers to the container if the container required it. While assigning properties like height, width, bit rate and so forth to the avcodec_context, I added

if (container_format_context->oformat->flags & AVFMT_GLOBALHEADER) {
    avcodec_context->flags |= CODEC_FLAG_GLOBAL_HEADER;
}

which seems to have fixed the issue.