Re: [FFmpeg-devel] [PATCH] avformat/aea: Add aea muxer

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

asivery via ffmpeg-devel:
> +typedef struct {
> +    int block_count;
> +} AeaMuxerContext;
> +
> +static int aea_init(AVFormatContext *s)
> +{
> +    AeaMuxerContext *c = s->priv_data;
> +    c->block_count = 0;

Unnecessary: A muxer's priv_data is always pre-zeroed.

> +    
> +    return 0;
> +}
> +
> +static int aea_write_header(AVFormatContext *s)
> +{
> +    AVDictionaryEntry *title_entry;

const

> +    int title_length = 0, i;
> +    char* title_contents;
> +    AVStream *st;
> +
> +
> +    if (s->nb_streams > 1) {
> +        av_log(s, AV_LOG_WARNING, "Got more than one stream to encode, they will be ignored.\n");

We don't ignore extraneous streams, we normally error out if something
like this happens.

> +    }
> +    
> +    st = s->streams[0];
> +    if (st->codecpar->ch_layout.nb_channels != 1 && st->codecpar->ch_layout.nb_channels != 2) {
> +        av_log(s, AV_LOG_ERROR, "Invalid amount of channels to mux (%d).\n", st->codecpar->ch_layout.nb_channels);
> +        return AVERROR(EINVAL);
> +    }
> +
> +    if (st->codecpar->sample_rate != 44100) {
> +        av_log(s, AV_LOG_ERROR, "Invalid sample rate (%d) AEA only supports 44.1kHz.\n", st->codecpar->sample_rate);
> +        return AVERROR(EINVAL);
> +    }
> +
> +    /* Write magic */
> +    avio_wl32(s->pb, 2048);
> +    
> +    /* Write AEA title */
> +    title_entry = av_dict_get(st->metadata, "title", NULL, 0);
> +    if (title_entry) {
> +        title_contents = title_entry->value;
> +        title_length = FFMIN(256, strlen(title_contents));

Don't use strlen() in FFMIN (like many macros, it can evaluate its
argument multiple times).

> +    }
> +
> +    if (title_length) {
> +        avio_write(s->pb, title_contents, title_length);
> +    }

No need for this branch, just call this inside the "if (title_entry)"
block above.

> +
> +    for (i = 0; i<(256 - title_length); i++) {
> +        avio_w8(s->pb, 0);
> +    }

ffio_fill(). Same below.

> +
> +    /* Write number of frames (zero at header-writing time, will seek later), number of channels */
> +    avio_wl32(s->pb, 0);
> +    avio_w8(s->pb, st->codecpar->ch_layout.nb_channels);
> +    avio_w8(s->pb, 0);
> +
> +    /* Write flags (meaning unknown) */ 
> +    for(i = 0; i<11; i++) {
> +        avio_wl32(s->pb, 0);
> +    }
> +
> +    /* Pad the header to 2048 bytes */
> +    for(i = 0; i<1738; i++) avio_w8(s->pb, 0);
> +
> +    return 0;
> +}
> +
> +static int aea_write_packet(struct AVFormatContext *s, AVPacket *pkt)
> +{
> +    AeaMuxerContext *c = s->priv_data;
> +    c->block_count++;
> +
> +    avio_write(s->pb, pkt->data, pkt->size);
> +    return 0;

You can avoid this and the whole muxer context by using
ff_raw_write_packet() and relying on AVStream.nb_frames.

> +}
> +
> +static int aea_write_trailer(struct AVFormatContext *s)
> +{
> +    AVIOContext *pb = s->pb;
> +    AeaMuxerContext *c = s->priv_data;
> +    if (pb->seekable & AVIO_SEEKABLE_NORMAL) {
> +        /* Seek to rewrite the block count. */
> +        avio_seek(pb, 260, SEEK_SET);
> +        avio_wl32(pb, c->block_count * s->streams[0]->codecpar->ch_layout.nb_channels);
> +    } else {
> +        av_log(s, AV_LOG_WARNING, "unable to rewrite AEA header.\n");
> +    }
> +
> +    return 0;
> +}
> +
> +const FFOutputFormat ff_aea_muxer = {
> +    .p.name           = "aea",
> +    .p.long_name      = NULL_IF_CONFIG_SMALL("MD STUDIO audio"),
> +    .priv_data_size   = sizeof(AeaMuxerContext),
> +    .p.extensions     = "aea",
> +    .p.audio_codec    = AV_CODEC_ID_ATRAC1,
> +    .init             = aea_init,
> +
> +    .write_header     = aea_write_header,
> +    .write_packet     = aea_write_packet,
> +    .write_trailer    = aea_write_trailer,
> +    .p.flags          = AVFMT_GENERIC_INDEX,

Makes no sense for a muxer.

> +};

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